2
Rise of Earthquake Science

Earthquakes have engaged human inquiry since ancient times, but the scientific study of earthquakes is a fairly recent endeavor. Instrumental recordings of earthquakes were not made until the last quarter of the nineteenth century, and the primary mechanism for the generation of earthquake waves—the release of accumulated strain by sudden slippage on a fault—was not widely recognized until the beginning of the twentieth century. The rise of earthquake science during the last hundred years illustrates how the field has progressed through a deep interplay among the disciplines of geology, physics, and engineering (1). This chapter presents a historical narrative of the development of the basic concepts of earthquake science that sets the stage for later parts of the report, and it concludes with some historical lessons applicable to future research.

2.1 EARLY SPECULATIONS

Ancient societies often developed religious and animistic explanations of earthquakes. Hellenic mythology attributed the phenomenon to Poseidon, the god of the sea, perhaps because of the association of seismic shaking with tsunamis, which are common in the northeastern Mediterranean (Figure 2.1). Elsewhere, earthquakes were connected with the movements of animals: a spider or catfish (Japan), a mole or elephant (India), an ox (Turkey), a hog (Mongolia), and a tortoise (Native America). The Norse attributed earthquakes to subterranean writhing of the imprisoned god Loki in his vain attempt to avoid venom dripping from a serpent’s tooth.



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2 Rise of Earthquake Science Earthquakes have engaged human inquiry since ancient times, but the scientific study of earthquakes is a fairly recent endeavor. Instrumental recordings of earthquakes were not made until the last quarter of the nineteenth century, and the primary mechanism for the generation of earthquake waves—the release of accumulated strain by sudden slippage on a fault—was not widely recognized until the beginning of the twentieth century. The rise of earthquake science during the last hundred years illustrates how the field has progressed through a deep interplay among the disciplines of geology, physics, and engineering (1). This chapter presents a historical narrative of the development of the basic concepts of earthquake science that sets the stage for later parts of the report, and it concludes with some historical lessons applicable to future research. 2.1 EARLY SPECULATIONS Ancient societies often developed religious and animistic explanations of earthquakes. Hellenic mythology attributed the phenomenon to Poseidon, the god of the sea, perhaps because of the association of seismic shaking with tsunamis, which are common in the northeastern Mediterranean (Figure 2.1). Elsewhere, earthquakes were connected with the movements of animals: a spider or catfish (Japan), a mole or elephant (India), an ox (Turkey), a hog (Mongolia), and a tortoise (Native America). The Norse attributed earthquakes to subterranean writhing of the imprisoned god Loki in his vain attempt to avoid venom dripping from a serpent’s tooth.

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FIGURE 2.1 The fallen columns in Susita (Hypos) east of the Sea of Galilee from a magnitude ~7.5 earthquake on the Dead Sea transform fault in A.D. 749. SOURCE: A. Nur, And the walls came tumbling down, New Scientist, 6, 45-48, 1991. Copyright A. Nur. Some sought secular explanations for earthquakes and their apocalyptic consequences (Box 2.1, Figure 2.2). For example, in 31 B.C. a strong earthquake devastated Judea, and the historian Josephus recorded a speech by King Herod given to raise the morale of his army in its aftermath (2): “Do not disturb yourselves at the quaking of inanimate creatures, nor do you imagine that this earthquake is a sign of another calam-

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BOX 2.1 Ruins of the Ancient World The collision of the African and Eurasian plates causes powerful earthquakes in the Mediterranean and Middle East. Some historical accounts document the damage from particular events. For example, a Crusader castle overlooking the Jordan River in present-day Syria was sheared by a fault that ruptured it at dawn on May 20, 1202.1 In most cases, however, such detailed records have been lost, so that the history of seismic destruction can be inferred only from archaeological evidence. Among the most convincing is the presence of crushed skeletons, which are not easily attributable to other natural disasters or war and have been found in the ruins of many Bronze Age cities, including Knossos, Troy, Mycenae, Thebes, Midea, Jericho, and Megiddo. Recurring earthquakes may explain the repeated destruction of Troy, Jericho, and Megiddo, all built near major active faults. Excavation of the ancient city of Megiddo—Armageddon in the Biblical prophecy of the Apocalypse—reveals at least four episodes of massive destruction, as indicated by widespread debris, broken pottery, and crushed skeletons.2 Similarly, a series of devastating earthquakes could have destabilized highly centralized Bronze Age societies by damaging their centers of power and leaving them vulnerable to revolts and invasions.3 Historical accounts document such “conflicts of opportunity” in the aftermath of earthquakes in Jericho (~1300 B.C.), Sparta (464 B.C.), and Jerusalem (31 B.C.). 1   R. Ellenblum, S. Marco, A. Agnon, T. Rockwell, and A. Boas, Crusader castle torn apart by earthquake at dawn, 20 May 1202, Geology, 26, 303-306, 1998. 2   A. Nur and H. Ron, Armageddon’s earthquakes, Int. Geol. Rev., 39, 532-541, 1997. 3   A. Nur, The end of the Bronze Age by large earthquakes? in Natural Catastrophes During Bronze Age Civilisations, B.J. Peisner, T. Palmer, and M.E. Bailey, eds., British Archaeological Review International, Series 728, Oxford, pp. 140-147, 1998. ity; for such affections of the elements are according to the course of nature, nor does it import anything further to men than what mischief it does immediately of itself.” Several centuries before Herod’s speech, Greek philosophers had developed a variety of theories about natural origins of seismic tremors based on the motion of subterranean seas (Thales), the falling of huge blocks of rock in deep caverns (Anaximenes), and the action of internal fires (Anaxagoras). Aristotle in his Meteorologica (about 340 B.C.) linked earthquakes with atmospheric events, proposing that wind in underground caverns produced fires, much as thunderstorms produced lightning. The bursting of these fires through the surrounding rock, as well as the collapse of the caverns burned by the fires, generated the earthquakes. In support of this hypothesis, Aristotle cited his observation that earthquakes tended to occur in areas with caves. He also classified earthquakes according to whether the ground motions were primarily vertical or hori-

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FIGURE 2.2 The remains of a family—a man, woman, and child (small skull visible next to the woman’s skull)—crushed to death in A.D. 365 in the city of Kourian on the island of Cyprus when their dwelling collapsed on top of them during an earthquake. SOURCE: D. Soren, The day the world ended at Kourion, National Geographic, 30-53, July 1988; Copyright Martha Cooper. zontal and whether they released vapor from the ground. He noted that “places whose subsoil is poor are shaken more because of the large amount of the wind they absorb.” The correlation he observed between the intensity of the ground motions and the weakness of the rocks on which structures are built remains central to seismic hazard analysis.

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2.2 DISCOVERY OF SEISMIC FAULTING Aristotle’s ideas and their variants persisted well into the nineteenth century (3). In the early 1800s, geology was a new scientific discipline, and most of its practitioners believed that volcanism caused earthquakes, both of which are common in geologically active regions. A vigorous adherent to the volcanic theory was the Irish engineer Robert Mallet, who coined the term seismology in his quantitative study of the 1857 earthquake in southern Italy (4). By this time, however, evidence had been accumulating that earthquakes are incremental episodes in the building of mountain belts and other large crustal structures, a process that geologists named tectonics. Charles Lyell, in the fifth edition of his seminal book The Principles of Geology (1837), was among the first to recognize that large earthquakes sometimes accompany abrupt changes in the ground surface (5). He based this conclusion on reports of the 1819 Rann of Cutch (Kachchh) earthquake in western India—near the disastrous January 26, 2001, Bhuj earthquake— and, in later editions, on the Wairarapa, New Zealand, earthquake of 1855. A protégé of Lyell’s, Charles Darwin, experienced a great earthquake while visiting Chile in 1835 during his voyages on the H.M.S. Beagle. Following the earthquake, he and Captain FitzRoy noticed that in many places the coastline had risen several meters, causing barnacles to die because of prolonged exposure to air. He also noticed marine fossils in sediments hundreds of meters above the sea and concluded that seismic uplift was the mechanism by which the mountains of the coast had risen. Darwin applied James Hutton’s principle of uniformitarianism—“the present is the key to the past”—and inferred that the mountain range had been uplifted incrementally by many earthquakes over many millennia (6). Fault Slippage as the Geological Cause of Earthquakes The leap from these observations to the conclusion that earthquakes result from slippage on geological faults was not a small one. The vast majority of earthquakes are accompanied by no surface faulting, and even when such ruptures had been found, questions arose as to whether the ground breaking shook the Earth or the Earth shaking broke the ground. Moreover, the methodology for mapping fault displacements and understanding their relationships to geological deformations, the discipline of structural geology, had not yet been systematized. A series of field studies—by G.K. Gilbert in California (1872), A. McKay in New Zealand (1888), B. Koto in Japan (1891), and C.L. Griesbach in Baluchistan (1892)—demonstrated that fault motion generates earthquakes, thereby documenting that the surface faulting associated with each of these earthquakes was consistent with the long-term, regional tectonic deformation that geologists had mapped (Figure 2.3).

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FIGURE 2.3 Photograph of the 1891 Nobi (Mino-Owari) earthquake scarp at Midori, taken by B. Koto, a professor of geology at the Imperial University of Tokyo. Based on his geological investigations, Koto concluded, “The sudden elevations, depressions, or lateral shiftings of large tracts of country that take place at the time of destructive earthquakes are usually considered as the effects rather than the cause of subterranean commotion; but in my opinion it can be confidently asserted that the sudden formation of the ‘great fault of Neo’ was the actual cause of the great earthquake.” This photograph appeared in The Great Earthquake in Japan, 1891, published by the Seismological Society of Japan, which was one of the first comprehensive scientific reports of an earthquake. The damage caused by the Nobi earthquake motivated Japan to create an Earthquake Investigation Committee, which set up the first government-sponsored research program on the causes and effects of earthquakes. SOURCE: J. Milne and W.K. Burton, The Great Earthquake in Japan, 1891, 2nd ed., Lane, Crawford & Co., Yokohama, Japan, 69 pp. + 30 plates, 1892. Among the geological investigations of this early phase of tectonics, Gilbert’s studies in the western United States were seminal for earthquake science. From the new fault scarps of the 1872 Owens Valley earthquake, he observed that the Sierra Nevada, bounding the west side of the valley, had moved upward and away from the valley floor. This type of faulting was consistent with his theory that the Basin and Range Province between the Sierra Nevada and the Wasatch Mountains of Utah had been formed by tectonic extension (7). He also recognized the similarity of the

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FIGURE 2.4 Aerial view, Salt Lake City, showing the scarps of active normal faults of the Wasatch Front, first recognized by G.K. Gilbert. SOURCE: Utah Geological Survey. Owens Valley break to a series of similar piedmont scarps along the Wasatch Front near Salt Lake City (Figure 2.4). By careful geological analysis, he documented that the Wasatch scarps were probably caused by individual fault movements during the recent geological past. This work laid the foundation for paleoseismology, the subdiscipline of geology that employs features of the geological record to deduce the fault displacement and age of individual, prehistoric earthquakes (8). Geological studies were supplemented by the new techniques of geodesy, which provide precise data on crustal deformations. Geodesy grew out of two practical arts, astronomical positioning and land surveying, and became established as a field of scientific study in the mid-nineteenth century. One of the first earthquakes to be measured geodetically was the Tapanuli earthquake of May 17, 1892, in Sumatra, which happened during a triangulation survey by the Dutch Geodetic Survey. The surveyor in charge, J.J.A. Müller, discovered that the angles between the survey monuments had changed during the earthquake, and he concluded that a horizontal displacement of at least 2 meters had occurred along a structure later recognized to be a branch of the Great Sumatran fault. R.D. Oldham

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of the Geological Survey of India inferred that the changes in survey angles and elevations following the great Assam earthquake of June 12, 1897, were due to co-seismic tectonic movements. C.S. Middlemiss reached the same conclusion for the Kangra earthquake of April 4, 1905, also in the well-surveyed foothills of the Himalaya (9). Mechanical Theories of Faulting The notion that earthquakes result from fault movements linked the geophysical disciplines of seismology and geodesy directly to structural geology and tectonics, whose practitioners sought to explain the form, arrangement, and interrelationships among the rock structures in the upper part of the Earth’s crust. Although Hutton, Lyell, and the other founders of the discipline of geology had investigated the great vertical deformations required by the rise of mountain belts, the association of these deformations with large horizontal movements was not established until the latter part of the nineteenth century (10). Geological mapping showed that some horizontal movements could be accommodated by the ductile folding of sedimentary strata and plastic distortion of igneous rocks, but that much of the deformation takes place as cataclastic flow (i.e., as slippage in thin zones of failure in the brittle materials that make up the outer layers of the crust). Planes of failure on the larger geological scales are referred to as faults, classified as normal, reverse, or strike-slip according to their orientation and the direction of slip (Figure 2.5). In 1905, E.M. Anderson (11) developed a successful theory of these faulting types, based on the premises that one of the principal compressive stresses is oriented vertically and that failure is initiated according to a rule published in 1781 by the French engineer and mathematician Charles Augustin de Coulomb. The Coulomb criterion states that slippage occurs when the shear stress on a plane reaches a critical value tc that depends linearly on the effective normal stress sneff acting across that plane: tc = t0 + µsneff, (2.1) where t0 is the (zero-pressure) cohesive strength of the rock and µ is a dimensionless number called the coefficient of internal friction, which usually lies between 0.5 and 1.0. Anderson’s theory made quantitative predictions about the angles of shallow faulting that fit the observations rather well (except in regions where fault planes were controlled by strength anisotropy like sedimentary layering). However, it could not explain the existence of large, nearly horizontal thrust sheets that formed at deeper structural levels in many mountain belts. Owing to the large lithostatic load, the total normal stress sn acting on such fault planes was

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FIGURE 2.5 Fault types showing principal stress axes and Coulomb angles. For a typical coefficient of friction in rocks (µ ˜ 0.6), the Coulomb criterion (Equation 2.1) implies that a homogeneous, isotropic material should fail under triaxial stress (s1 > s2 > s3) along a plane that contains the s2 axis and lies at an angle about 30° to the s1 direction. According to Anderson’s theory, normal faults should therefore occur where the vertical stress sV is the maximum principal stress s1, and the initial dips of these extensional faults should be steep (about 60°); reverse faults (sV = s3) should initiate as thrusts with shallow dips of about 30°, and strike-slip faults (sV = s2) should develop as vertical planes striking at about 30° to the s1 direction. SOURCE: Reprinted from K. Mogi, Earthquake Prediction, Academic Press, Tokyo, 355 pp., 1985, Copyright 1985 with permission from Elsevier Science. much greater than any plausible tectonic shear stress, so it was difficult to see how failure could happen. M.K. Hubbert and W.W. Rubey resolved this quandary in 1959 (12) by recognizing that the effective normal stress in the Coulomb criterion should be the difference between sn and the fluid pressure Pf: sneff = sn – Pf. (2.2) They proposed that overthrust zones were overpressurized; that is Pf in these zones was substantially greater than the pressure expected for hydrostatic equilibrium and could approach lithostatic values (13). Hence, sneff could be much smaller than sn. Overpressurization may explain why some faults, such as California’s San Andreas, appear to be exceptionally weak. Elastic Rebound Model When a 470-kilometer segment of the newly recognized San Andreas rift ruptured across northern California in 1906 (Box 2.2, Figures 2.6 and 2.7), both geologists and engineers jumped at the opportunity to observe first-hand the effects of a major earthquake. Three days after the earthquake, while the fires of San Francisco were still smoldering, California Governor George C. Pardee appointed a State Earthquake Investigation

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BOX 2.2 San Francisco, California, 1906 At approximately 5:12 a.m. local time on April 18, 1906, a small fracture nucleated on the San Andreas fault at a depth of about 10 kilometers beneath the Golden Gate (20). The rupture expanded outward, quickly reaching its terminal velocity of about 2.5 kilometers per second (5600 miles per hour). Its upper front broke through the ground surface at the epicenter within a few seconds, and its lower front decelerated as it spread downward into the more ductile levels of the middle crust, while the two sides continued to propagate in opposite directions along the San Andreas. Near the epicenter, the rupture displaced the opposite sides of the fault rightward by an average of about 4 meters (a right-lateral strike-slip). On the southeastern branch, the total slip diminished as the rupture traveled down the San Francisco peninsula and vanished 100 kilometers away from the epicenter. To the northwest, the fracture ripped across the neck of the Point Reyes peninsula and entered Tomales Bay, where the total slip increased to 7 meters, sending out seismic waves that damaged Santa Rosa, Fort Ross, and other towns of the northern Coast Ranges. The rupture continued up the coast to Point Arena, where it went offshore, eventually stopping near a major bend in the fault at Cape Mendocino (Figure 2.6). At least 700 people were killed, perhaps as many as 3000, and many buildings were severely damaged.1 In San Francisco, the quake ignited at least 60 separate fires, which burned unabated for three days, consuming 42,000 buildings and destroying a considerable fraction of the West Coast’s largest city. 1   G. Hansen and E. Condon, Denial of Disaster: The Untold Story of the San Francisco Earthquake and Fire of 1906, Cameron and Co., San Francisco, 160 pp., 1989. These authors present evidence that the scale of the 1906 disaster, in terms of both property destroyed and lives lost, was deliberately underreported to protect economic interests. They also argue that the damage directly caused by the earthquake was preferentially reported as fire damage, because the latter was more likely to be covered by insurance. Commission, headed by Berkeley Professor Andrew C. Lawson, to coordinate a wide-ranging set of scientific and engineering studies (14). The first volume of the Lawson Report (1908) compiled reports by more than 20 specialists on a variety of observations: the geological setting of the San Andreas; the fault displacements inferred from field observations and geodetic measurements; reports of the arrival time, duration, and intensity of the seismic waves; seismographic recordings from around the world; and detailed surveys of the damage to structures throughout Northern California. The latter demonstrated that the destruction was closely related to building design and construction, as well as to local geology. The intensity maps of San Francisco clearly show that some of the strongest shaking occurred in the soft sediment of China Basin and in the present Marina district, two San Francisco neighborhoods that would be severely damaged in the Loma Prieta earthquake some 83 years later (15). This interdiscipli-

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FIGURE 2.6 San Andreas fault system in California, showing the extent of the surface rupture, damage area, and felt area of the 1906 earthquake. SOURCE: T.H. Jordan and J.B. Minster, Measuring crustal deformation in the American west, Sci. Am., 256, 48-58, 1988. Illustration by Hank Iken.

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83.   D. Griggs and J. Handin, Rock Deformation, Geological Society of America Memoir 79, Boulder, Colo., 382 pp., 1960. 84.   W.F. Brace and J.D. Byerlee, Stick slip as a mechanism for earthquakes, Science, 153, 990-992, 1966. In an early series of experiments at Harvard University, P.W. Bridgman (Shearing phenomena at high pressure of possible importance for geology, J. Geol., 44, 653-669, 1936) had observed strike-slip between thin layers of materials subjected to torsional stress. The term stick-slip was introduced by F.P. Bowden and L. Leben (The nature of sliding and the analysis of friction, Proc. R. Soc. Lond., A169, 371-391, 1939), and the theory was developed with a focus on machine engineering issues (E. Rabinowicz, Friction and Wear of Materials, John Wiley, New York, 50 pp., 1965). The phenomenon was notoriously difficult to study in the laboratory, however, primarily because most testing machines could not be adequately regulated to obtain reproducible results. Brace and Byerlee’s success depended on their use of a new, “stiffer” testing machine. 85.   W.F. Brace and J.D. Byerlee, California earthquakes: Why only shallow focus, Science, 168, 1575, 1968. 86.   Although Brace and Byerlee recognized the importance of the dynamical characteristics of the testing machine in the generation of stick-slip instabilities, a quantitative understanding of the dynamics of stable and unstable sliding was not achieved for another 10 years, when the concept of a critical stiffness kc was precisely formulated for strain-weakening materials (J.W. Rudnicki, The inception of faulting in a rock mass with a weakened zone, J. Geophys. Res., 82, 844-854, 1977). Instabilities associated with velocity-weakening “rate-state” constitutive laws were investigated later by J.R. Rice and A.L. Ruina (Stability of steady frictional slipping, J. Appl. Mech., 50, 343-349, 1983). 87.   F. Rummel and C. Fairhurst, Determination of the post-failure behavior of brittle rock using a servo-controlled testing machine, Rock Mech., 2, 189-204, 1970; R. Houpert, The uniaxial compressive strength of rocks, Proceedings of the 2nd International Society of Rock Mechanics, vol. II, Jaroslav Cerni Institute for Development of Water Resources, Belgrade, pp. 49-55, 1970; H.R. Hardy, R. Stefanko, and E.J. Kimble, An automated test facility for rock mechanics research, Int. J. Rock Mech. Min. Sci., 8, 17-28, 1971. 88.   Dilatancy is the volume expansion due to the application of a shear stress, a well-known property of granular materials. Brace and his colleagues observed this phenomenon during rock-shearing experiments in the laboratory, which they interpreted as being due to pervasive microcracking in their specimens with a concomitant increase in void space (W.R. Brace, B.W. Paulding, and C.H. Scholz, Dilatancy of the fracture of crystalline rocks, J. Geophys. Res., 71, 3939-3953, 1966). 89.   T.E. Tullis and J.D. Weeks, Constitutive behavior and stability of frictional sliding of granite, Pure Appl. Geophys., 124, 10-42, 1986; N.M. Beeler, T.E. Tullis, M.L. Blanpied, and J.D. Weeks, Frictional behavior of large displacement experimental faults, J. Geophys. Res., 101, 8697-8715, 1996. 90.   J.H. Dieterich, Time-dependent friction in rocks, J. Geophys. Res., 77, 3690-3697, 1972. 91.   C. Scholz, P. Molnar, and T. Johnson, Frictional sliding of granite and earthquake mechanism implications, J. Geophys. Res., 77, 6392-6406, 1972. 92.   J.H. Dieterich, Time-dependent friction and the mechanics of stick-slip, Pure Appl. Geophys., 116, 790-806, 1978. The concept of a critical slip distance as a parameter characterizing frictional changes was first introduced by E. Rabinowicz (The nature of static and kinetic coefficients of friction, J. Appl. Phys., 22, 1373-1379, 1951; The intrinsic variables affecting the stick-slip process, Proc. R. Soc. Lond., A71, 668-675, 1958), who interpreted it as the typical dimension of surface contact junctions. 93.   J.H. Dieterich, Modelling of rock friction 1. Experimental results and constitutive equations, J. Geophys. Res., 84, 2161-2168, 1979; J.H. Dieterich, Constitutive properties of faults with simulated gouge, in Mechanical Behavior of Crustal Rocks, N.L. Carter, M. Friedman, J.M.

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    Logan, and D.W. Sterns, eds., American Geophysical Union Monograph 24, Washington, D.C., pp. 103-120, 1981; A. Ruina, Slip instability and state variable friction laws, J. Geophys. Res., 88, 10,359-10,370, 1983 (see also J.R. Rice, Constitutive relations for fault slip and earthquake instabilities, Pure Appl. Geophys., 121, 443-475, 1983). The historical development of the rate-state theory is summarized in the review papers by C. Marone (Laboratory-derived friction laws and their application to seismic faulting, Ann. Rev. Earth Planet. Sci., 26, 643-696, 1998) and C.H. Scholz (Earthquakes and friction laws, Nature, 391, 37-42, 1998). 94.   S.T. Tse and J.R. Rice, Crustal earthquake instability in relation to the depth variation of frictional slip properties, J. Geophys. Res., 91, 9452-9472, 1986. Subsequent depth-variable crustal models were based on friction data for saturated granite gouge studied over the range of crustal temperatures by M.L. Blanpied, D.A. Lockner, and J.D. Byerlee (Fault stability inferred from granite sliding experiments at hydrothermal conditions, Geophys. Res. Letters, 18, 609-612, 1991; Frictional slip of granite at hydrothermal conditions, J. Geophys. Res., 100, 13,045-13,064, 1995); a recent example is N. Lapusta, J.R. Rice, Y. BenZion, and G. Zheng, Elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate- and state-dependent friction, J. Geophys. Res.,105, 23,765-23,789, 2000. 95.   K. Aki, Generation, propagation of G waves, Niigata earthquake 1964 June 16. Pt 1, Bull. Earthquake Res. Inst. Tokyo Univ., 44, 23-88, 1966. Formally speaking, the right-hand side of Equation 2.6 is the static moment, so that an accurate estimate of M0 for an earthquake of finite size requires the measurement of waves whose periods are long compared to the duration of the faulting. For the 1964 Niigata earthquake, Aki used surface waves with periods up to 200 seconds, which satisfied this criterion. He found M0 ˜ 3 × 1020 newton-meters. 96.   Moment magnitude MW was introduced by H. Kanamori (The energy release in great earthquakes, J. Geophys. Res., 82, 2981-2987, 1977; Quantification of earthquakes, Nature, 271, 411-414, 1978), and its agreement with other magnitude scales in their unsaturated ranges was discussed by T.C. Hanks and H. Kanamori (A moment magnitude scale, J. Geophys. Res., 84, 2348-2350, 1979). 97.   Omori established his empirical hyperbolic law of aftershock frequency, n(t) ~ t–1, in his studies of the 1891 Nobi earthquake (F. Omori, On aftershocks, Report by the Earthquake Investigation Committee, 2, 103-139, 1894; ibid., Report by the Earthquake Investigation Committee, 30, 4-29, 1900). This relationship was extended first by R. Hirano and later by T. Utsu (A statistical study on the occurrence of aftershocks, Geophys. Mag., 30, 521-605, 1961) to a power law in the form of Equation 2.8, which is now called the modified Omori law. 98.   The first detailed study of aftershocks using portable seismometers was conducted by Caltech seismologists following the 1952 Kern County earthquake in central California (H. Benioff, Earthquakes in Kern County, California, 1952, California Division of Mines, State of California, Bulletin 171, 283 pp., 1955). Based on this and other data, Benioff (Seismic evidence for crustal structure and tectonic activity, in Crust of the Earth. A Symposium, A Poldervaart, ed., Geological Society of America, New York, pp. 61-75, 1955) hypothesized that the spatial distribution of aftershocks defines the segment of the fault that had ruptured during the mainshock. Subsequent work has shown this to be approximately true for the initial sequence of aftershocks, although the aftershock zone typically expands to a larger area after a week or so (F. Tajima and H. Kanamori, Global survey of aftershock area expansion patterns, Phys. Earth Planet. Int., 40, 77-134, 1985). 99.   K. Aki used a spectral representation to establish that earthquakes of varying size had spectra of similar shape, differing primarily in the low-frequency amplitude, proportional to seismic moment, and the location of the “characteristic frequency,” which he related to the characteristic length scale of an earthquake (Scaling law of seismic spectrum, J. Geophys. Res., 72, 1217-1231, 1967). Subsequent studies by J.N. Brune (Tectonic stress and

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    the spectra of seismic shear waves from earthquakes, J. Geophys. Res., 75, 4997-5009, 1970) and J.C. Savage (Relation of corner frequency to fault dimensions, J. Geophys. Res., 77, 3788-3795, 1972) related the corner frequency to the dimensions of the fault plane. 100.   Theoretical studies of propagating fractures by the engineer G.R. Irwin and his associates (see L.B. Freund, Dynamic Fracture Mechanics, Cambridge University Press, Cambridge, U.K., 563 pp., 1990) had shown that the speed limit for an antiplane crack (slip direction parallel to the dislocation line) was the shear-wave velocity vS, while that for an in-plane crack (slip direction perpendicular to the dislocation line) was the Rayleigh-wave velocity. Seismological observations indicated that the actual rupture velocities for earthquakes are 10-20 percent lower than these theoretical limits. 101.   This equation for the stress drop omits a nondimensional scaling constant cs of order unity, which depends on the rupture geometry. V. Keilis Borok (On the estimation of the displacement in an earthquake source and of source dimensions, Ann. Geofisica, 12, 205-214, 1959) derived cs = 7p/16 ˜ 1.37 for a circular crack, and he applied this formula to obtain a stress drop for the 1906 San Francisco earthquake. 102.   The observation that the static stress drop is approximately constant for earthquakes of different sizes in similar tectonic environments was established in publications by K. Aki (e.g., Earthquake mechanism, Tectonophysics, 13, 423-446, 1972) and various other authors in the early 1970s; see the summary by T. Hanks (Earthquake stress drops, ambient tectonic stresses and stresses that drive plate motions, Pure Appl. Geophys., 115, 441-458, 1977). 103.   H. Kanamori and D.L. Anderson, Theoretical basis of some empirical relations in seismology, Bull. Seis. Soc. Am., 65, 1073-1095, 1975. 104.   N. Haskell, Total energy and energy spectral density of elastic wave radiation from propagating faults, Bull. Seis. Soc. Am., 54, 1811-1842, 1964. 105.   N. Haskell, Total energy and energy spectral density of elastic wave radiation from propagating faults, 2, A statistical source model, Bull. Seis. Soc. Am., 56, 125-140, 1966; K. Aki, Scaling law of seismic spectrum, J. Geophys. Res., 72, 1217-1231, 1967. 106.   B.V. Kostrov, Teoriya ochagov tektonicheskikh zemletryaseniy. Tectonic earthquake focal theory, Izv. Akad. Nauk. S.S.R., Earth Physics, 4, 84-101, 1970; M.J. Randall, Elastic multiple theory and seismic moment, Bull. Seis. Soc. Am., 61, 1321-1326, 1971; F. Gilbert, Excitation of the normal modes of the earth by earthquake sources, Geophys. J. R. Astr. Soc., 22, 223-226, 1971. The moment tensor can be represented a 3 × 3 matrix, which must be symmetric to conserve angular momentum; the most general moment tensor is therefore specified by six real numbers. 107.   L. Knopoff and M.J. Randall, Compensated linear-vector dipole-possible mechanism of deep earthquakes, J. Geophys. Res., 75, 4957-4963, 1970. A CLVD represents the strain associated with a volume-preserving extension (or compression) of an infinitesimal cylinder along its axis of symmetry. The evidence and interpretation of earthquake focal mechanisms that do not conform to simple double couples have recently been reviewed by B.R. Julian, A.D. Miller, and G.R. Foulger, Non-double-couple earthquakes: 1. Theory, Rev. Geophys., 36, 525-549, 1998. 108.   D. Forsyth and S. Uyeda (On the relative importance of the driving forces of plate motion, Geophys. J. Roy. Astr. Soc., 43, 163-200, 1975) showed that the primary driving forces are “ridge push” (compression due to gravitational sliding of newly formed lithosphere away from mid-ocean ridge highs) and “slab pull” (tension due to the gravitational sinking of the old subducting slabs). Subsequent analyses attempted to explain plate motions using the lateral density variations inferred from seismic tomography as the buoyancy forces in self-consistent models of mantle convection (B.H. Hager and R.J. O’Connell, A simple global model of plate dynamics and mantle convection, J. Geophys. Res., 86, 4843-4867, 1981; Y. Ricard and C. Vigny, Mantle dynamics with induced plate tectonics, J. Geophys. Res., 94,

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    17,543-17,559, 1989; C.W. Gable, R.J. O’Connell, and B.J. Travis, Convection in three dimensions with surface plates: Generation of toroidal flow, J. Geophys. Res., 96, 8391-8405, 1991). 109.   Some intraplate earthquakes occur along preexisting zones of weakness in the continental crust associated with the landward extensions of oceanic fracture zones (L.R. Sykes, Intraplate seismicity reactivation of preexisting zones of weakness, alkaline magmatism, and other tectonism postdating continental fragmentation, Rev. Geophys. Space Phys., 16, 621-688, 1978), and some occur along reactivated faults that were first formed during continental rifting (A.C. Johnston, K.H. Coppersmith, L.R. Kanter, and C.A. Cornell, The Earthquakes of Stable Continental Regions: Assessment of Large Earthquake Potential, J.F. Schneider, ed., Electric Power Research Institute, Technical Report 102261, Palo Alto, Calif., 4 vols., 2985 pp., 1994). 110.   At 10-kilometer depth, the effective normal stress sneff is about 180 megapascals (assuming hydrostatic pore pressure Pf), so that reasonable values of the coefficient of friction (µ = 0.6-0.8) imply that the shear stress to initiate frictional slip should be 110-140 megapascals. 111.   The lack of detectable heat flow anomaly was first reported by J.N. Brune, T.L. Henyey, and R.F. Roy (Heat flow, stress and rate of slip along San Andreas fault, California, J. Geophys. Res., 74, 3821-3827, 1969) and confirmed by A.H. Lachenbruch and J.H. Sass (Thermo-mechanical aspects of the San Andreas fault system, in Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, R.L. Kovach and A. Nur, eds., Stanford University Publications in Geological Science 13, Stanford, Calif., pp. 192-205, 1973). Both of these studies quoted an upper bound on the average stress of 20 megapascals. 112.   The direction of maximum principal compressive stress can be constrained from the orientations of borehole breakouts, in some cases by direct stress measurements, and by the orientations of known faults and the inferred focal mechanism orientation for smaller earthquakes in a region (assuming that these involve slip in the maximally shear-stressed direction on the causative fault). Such data showed that the maximum principal stress direction near the San Andreas fault was steeply inclined to the fault trace, in places approaching 80 degrees, much different than the 30- to 45-degree inclination expected if the fault was the most highly stressed feature in the region and was close to frictional failure (V. Mount and J. Suppe, State of stress near the San Andreas Fault—Implications of wrench tectonics, Geology, 15, 1143-1146, 1987; M.D. Zoback, M.L. Zoback, V. Mount, J. Eaton, J. Healy, D. Oppenheimer, P. Reasenberg, L. Jones, B. Raleigh, I. Wong, O. Scotti, and C. Wentworth, New evidence on the state of stress of the San Andreas fault system, Science, 238, 1105-1111, 1988). 113.   S.H. Hickman, R.H. Sibson, and R.L. Bruhn, Introduction to special session: Mechanical involvement of fluids in faulting, J. Geophys. Res., 100, 12,831-12,840, 1995. 114.   Gilbert’s article “A Theory of the Earthquakes of the Great Basin, with a Practical Application” appeared in the Salt Lake City Tribune on September 30, 1883 (reprinted in Am. J. Sci., 3rd Ser., 27, 49-54, 1884). 115.   Recent paleoseismic studies have shown that during the last 6000 years, the Wasatch fault has not ruptured all at once along its entire 340-kilometer length, but rather in smaller independent segments (M.N. Machette, S.F. Personius, A.R. Nelson, D.P. Schwartz, and W.R. Lund, The Wasatch fault zone, J. Struct. Geol., 13, 137-149, 1991). About 10 such segments have been identified, ranging in length from about 11 to 70 kilometers. During the last 6000 years, one of these segments has ruptured every 350 years on average, producing earthquakes with magnitudes ranging from 6.5 to 7.5. Individual segments appear to show irregular patterns of recurrence, however, with interseismic intervals lasting as long as 4000 years. 116.   Reid’s comment about precursory strain is based on the geodetic measurements of displacement of the Farallon Islands in the half-century before the 1906 earthquake. This

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    motion, which was about half that of the co-seismic displacement, was a key observation in the development of his hypothesis. 117.   By “strong earthquake,” Reid clearly meant something like the 1906 San Francisco earthquake, and he was implicitly assuming a characteristic earthquake model. Modern geodetic measurements show a rate of angle change of a few hundred parts per billion per year, with very modest changes over time, in the region of the 1906 quake (W.H. Prescott and M. Lisowski, Strain accumulation along the San Andreas fault system east of San Francisco Bay, California, Tectonophysics, 97, 41-56, 1983). Thus, it would take a few thousand years to accumulate Reid’s critical strain of 1/2000. Recent paleoseismic investigations indicate that surface-rupturing earthquakes on the 1906 rupture zone have an average interval of a few hundred years (D.P. Schwartz, D. Pantosti, K. Okumura, T.J. Powers, J.C. Hamilton, Paleoseismic investigations in the Santa Cruz Mountains, California; Implications for recurrence of large-magnitude earthquakes on the San Andreas fault, J. Geophys. Res., 103, 17,985-18,001, 1998). Reid may have overestimated the critical strain, the paleo-earthquakes may not have all been as large as the 1906 event, or the strain may not have been reset to zero in 1906. 118.   K. Aki, Possibilities of seismology in the 1980s (Presidential address to the Seattle meeting), Bull. Seis. Soc. Am., 70, 1969-1976, 1980. Imamura is also reported to have forecast the occurrence of the great Nankaido earthquakes of 1944 and 1946 (On the seismic activity of central Japan, Jap. Jour. Astron. Geophys., 6, 119-137, 1928, Jap. Jour. Astron. Geophys., 6, 119-137, 1928; see S.P. Nishenko, Earthquakes, hazards and predictions, in The Encyclopeida of Solid-Earth Geophysics, D.E. James, ed., Van Nostrand Reinhold, New York, pp. 260-268, 1989). 119.   S.A. Fedotov, Regularities of distribution of strong earthquakes in Kamchatka, the Kuril Islands and northern Japan (in Russian), Akad. Nauk. SSSR Inst. Fiziki Zemli Trudi, 36, 66-93, 1965. Fedotov’s map of seismic gaps include earthquakes of M 7.75 and larger; it was reproduced by K. Mogi in Earthquake Prediction, Academic Press, London, p. 82, 1985. 120.   L.R. Sykes, Aftershock zones of great earthquakes, seismicity gaps and prediction, J. Geophys. Res.,76, 8021-8041, 1971. G. Plafker and M. Rubin (Uplift history and earthquake recurrence as deduced from marine terraces on Middleton Island, in Proceedings of Conference VI: Methodology for Identifying Seismic Gaps and Soon-to-Break Gaps, U.S. Geological Survey Open File Report 78-943, Reston, Va., pp. 687-722, 1978) later argued from direct geological evidence that this estimate of repeat time was short by a factor of two to four. 121.   C.G. Chase, The n plate problem of plate tectonics, Geophys. J. R. Astron. Soc., 29, 117-122, 1972; J.B. Minster, T.H. Jordan, P. Molnar, and E. Haines, Numerical modelling of instantaneous plate tectonics, Geophys. J. Roy. Astron. Soc., 36, 541-576, 1974; J.B. Minster and T.H. Jordan, Present-day plate motions, J. Geophys. Res., 83, 5331-5354, 1978. 122.   J.A. Kelleher, L.R. Sykes, and J. Oliver, Criteria for prediction of earthquake locations, Pacific and Caribbean, J. Geophys. Res., 78, 2547-2585, 1973; W.R. McCann, S.P. Nishenko, L.R. Sykes, and J. Krause, Seismic gaps and plate tectonics: Seismic potential for major boundaries, Pure App. Geophys., 117, 1082-1147, 1979. McCann et al. defined seismic gap as follows: “The term seismic gap is taken to refer to any region along an active plate boundary that has not experienced a large thrust or strike slip earthquake for more than 30 years … Segments of plate boundaries that have not been the site of large earthquakes for tens to hundreds of years (i.e., have been seismic gaps for large shocks) are more likely to be the sites of future large shocks than segments that experience rupture during, say, the last 30 years.” 123.   S.P. Nishenko, Circum-Pacific seismic potential: 1989-1999, Pure Appl. Geophys., 135, 169-259, 1991. Nishenko defined for each of 98 plate boundary segments a characteristic earthquake with a magnitude sufficient to rupture the entire segment, and a probability that such an earthquake would occur within 5, 10, and 20 years beginning in 1989 was

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    specified. The probability was based on the assumption that characteristic earthquakes are quasi periodic, with an average recurrence time that can be estimated from historic earthquakes or from the rates of relative plate motion. In the latter method, the mean recurrence time is estimated from the ratio of the average displacement in a characteristic earthquake to the relative plate velocity. 124.   D.P. Schwatz and K.J. Coppersmith, Fault behavior and characteristic earthquakes: Examples from the Wasatch and San Andreas faults, J. Geophys. Res., 89, 5681-5698, 1984. 125.   T. Hirata, Fractal dimension of fault systems in Japan: Fractal structure in rock fracture geometry at various scales, Pure Appl. Geophys., 131, 157-170, 1989; P. Segall and D. Pollard, Joint formation in granitic rock of the Sierra Nevada, Geol. Soc. Am. Bull., 94, 563-575, 1983; S. Wesnousky, C. Scholz, and K. Shimazaki, Earthquake frequency distribution and the mechanics of faulting, J. Geophys. Res., 88, 9331-9340, 1983. 126.   In principle, the characteristic magnitude can be determined from the magnitudes of previous earthquakes on a fault segment or estimated from the length or area of the segment. Both methods present practical difficulties. Because the characteristic magnitude is thought to vary by segment, only events on a specific segment pertain. Uncertainties in magnitude and location of early quakes make it difficult to identify truly characteristic earthquakes in the seismic or geologic record. Fault geometry is not very definitive because there is insufficient understanding of the fault features that would prevent earthquake rupture from propagating further. S. Wesnousky (The Gutenberg-Richter or characteristic earthquake distribution: Which is it?, Bull. Seis. Soc. Am., 84, 1940-1959, 1994) examined the magnitude distribution on large sections of the San Andreas and other faults. He compared the rate of large earthquakes required to match the observed fault slip with that inferred by extrapolating the rate of smaller events with the Gutenberg-Richter relationship. For several sections, he found that the rate based on fault slip exceeded the Gutenberg-Richter rate, suggesting that the characteristic model was more appropriate there. However, Kagan disputed these findings (Y. Kagan and S. Wesnousky, The Gutenberg-Richter or characteristic earthquake distribution, Which is it? Discussion and reply, Bull. Seis. Soc. Am., 86, 274-291, 1996.). He argued that the result was biased because the regions were chosen around past earthquakes. Furthermore, the fault slip could be explained by a Gutenberg-Richter distribution if the maximum magnitude chosen was large enough. 127.   S.P. Nishenko (Earthquakes, hazards and predictions, in The Encyclopeida of Solid-Earth Geophysics, D.E. James, ed., Van Nostrand Reinhold, New York, pp. 260-268, 1989) listed 15 large earthquakes that occurred in previously identified seismic gaps, including 8 earthquakes of M 8 and larger. Y.Y. Kagan and D.D. Jackson (Seismic gap hypothesis, J. Geophys. Res., 96, 21,419-21,431, 1991) reevaluated Nishenko’s conclusions for the 10 events that occurred after Kelleher, Sykes, and Oliver (Possible criteria for predicting earthquake locations and their application to major plate boundaries of the Pacific and the Caribbean, J. Geophys. Res., 78, 2547-2585, 1973) provided geographically specific gap definitions. Kagan and Jackson found five unqualified successes, two mixed successes (earthquake on gap boundary), two events where gaps were not defined), and one earthquake in a “filled” gap. The track record of the gap hypothesis has been quite controversial, in part because early definitions were subjective. For further discussion, see S.P. Nishenko and L.R. Sykes, Comment on “Seismic gap hypothesis: Ten years after” by Y.Y. Kagan and D.D. Jackson, J. Geophys. Res., 98, 9909-9916, 1993; D.D. Jackson and Y.Y. Kagan, “Comment on ‘Seismic gap hypothesis: Ten years after”, Reply to S.P. Nishenko and L.R. Sykes, J. Geophys. Res., 98, 9917-9920, 1993; Y.Y. Kagan and D.D. Jackson, New seismic gap hypothesis: Five years after, J. Geophys. Res., 100, 3943-3959, 1995. 128.   K. Shimazaki and T. Nakata, Time-predictable recurrence model for large earthquakes, Geophys. Res. Lett., 7, 279-282, 1980. The time-predictable model had been proposed

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    earlier by C.G Bufe, P.W. Harsh, and R.O. Burford (Steady-state seismic slip—A precise recurrence model, Geophys. Res. Lett., 4, 91-94, 1977). 129.   The Japanese program for earthquake research, like its U.S. counterpart, is a broadly based, multidisciplinary effort directed at mitigating seismic hazards, but unlike the National Earthquake Hazards Reduction Program (NEHRP), its principal focus has been event-specific, “practical earthquake prediction.” The program involves six agencies, with the scientific lead given to the Japan Meteorological Agency. The total expenditures over the first 30 years of the program’s existence (1964-1993) were nearly 2000 × 108 yen, or about $1.7 billion (in as-spent dollars). In units of 108 yen (approximately $1 million), recent budgets for the program were 743 for 1995, 177 for 1996, and 214 for 1997. The 1995 number is high because it includes two supplements of 370 and 265 that were allocated following the destructive Hyogo-ken Nambu (Kobe) earthquake. The NEHRP expenditures for the same years, in millions of dollars, were 103, 106, and 98, respectively. The differences in expenditures between the two programs are even larger because the Japanese budgets do not include salaries, which are funded separately, whereas the U.S. budgets do. 130.   W.H. Bakun and A.G. Lindh, The Parkfield, California earthquake prediction experiment, Science, 229, 619-624, 1985. 131.   Postmortem explanations cover a wide range. The 1983 Coalinga earthquake may have reduced the stress (R.W. Simpson, S.S. Schulz, L.D. Dietz, and R.O. Burford, The response of creeping parts of the San Andreas fault to earthquakes on nearby faults: Two examples, Pure Appl. Geophys., 126, 665-685, 1988). The rate of Parkfield earthquakes may be slowing because of postseismic relaxation from 1906 (Y. Ben-Zion, J.R. Rice, and R. Dmowska, Interaction of the San Andreas fault creeping segment with adjacent great rupture zones, and earthquake recurrence at Parkfield, J. Geophys. Res., 98, 2135-2144, 1993), or the Parkfield sequence may be a chance occurrence rather than a characteristic earthquake sequence (Y.Y. Kagan, Statistical aspects of Parkfield earthquake sequence and Parkfield prediction, Tectonophysics, 270, 207-219, 1997). 132.   Working Group on California Earthquake Probabilities, Probabilities of Large Earthquakes Occurring in California on the San Andreas Fault, U.S. Geological Survey Open-File Report 88-398, Reston, Va., 62 pp., 1988. 133.   R.A. Harris summarized more than 20 published or broadcast statements that could be interpreted as scientific forecasts of the Loma Prieta earthquakes (Forecasts of the 1989 Loma Prieta, California, earthquake, Bull. Seis. Soc. Am., 88, 898-916, 1998). The 1906 surface displacement was smaller than it was to the north, suggesting incomplete release of the accumulated strain. Small earthquakes were notably absent on this segment, a pattern that was thought to appear before large earthquakes. From these observations, several earthquake forecasts were generated expressing the rupture length, magnitude, and approximate timing in probabilistic terms. For example, in 1983 Alan Lindh forecast an M 6.5 earthquake with a probability of 0.30 in 20 years (A.G. Lindh, Preliminary Assessment of Long-Term Probabilities for Large Earthquakes Along Selected Fault Segments of the San Andreas Fault System in California, U.S. Geological Survey Open-File Report 83-63, Menlo Park, Calif., 15 pp., 1983). In 1984 Sykes and Nishenko forecast an M 7.0 earthquake with a probability of 0.19 to 0.95 in 20 years (S.P. Nishenko, Probabilities of occurrence of large plate rupturing earthquakes for the San Andreas, San Jacinto, and Imperial faults, California, 1983-2003, J. Geophys. Res., 89, 5905-5927, 1984). 134.   The earthquake was not on the San Andreas fault in a strict sense, but rather on a subsidiary, the Sargent fault, that dips about 70 degrees to the southwest and does not intersect the San Andreas. The fault slip had a large vertical component, which was different from expected San Andreas motion. Moreover, historical strain data suggest that significant slip occurred at depth on the San Andreas fault during the 1906 earthquake, so there may have been little or no slip deficit to warrant the initial forecasts.

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135.   For a recent compilation, including long-, intermediate-, and short-term prediction, see the conference proceedings introduced by L. Knopoff, Earthquake prediction: The scientific challenge, Proc. Natl. Acad. Sci., 93, 3719-3720, 1996. Articles by many other authors follow in sequence. For a brief, cautiously skeptical review see D.L. Turcotte, Earthquake prediction, Ann. Rev. Earth Planet. Sci., 19, 263-281, 1991. For a detailed, negative assessment of the history of earthquake prediction research, see R.J. Geller, Earthquake prediction: A critical review, Geophys. J. Int., 131, 425-450, 1997. 136.   J. Deng and L. Sykes, Evolution of the stress field in southern California and triggering of moderate-size earthquakes; A 200-year perspective, J. Geophys. Res., 102, 9859-9886, 1997; R.A. Harris and R.W. Simpson, Stress relaxation shadows and the suppression of earthquakes; Some examples from California and their possible uses for earthquake hazard estimates, Seis. Res. Lett., 67, 40, 1996; R.A. Harris and R.W. Simpson, Suppression of large earthquakes by stress shadows; A comparison of Coulomb and rate-and-state failure, J. Geophys. Res., 103, 24,439-24,451, 1998. 137.   K. Mogi, Earthquake Prediction, Academic Press, Tokyo, 355 pp., 1985. Mogi’s “do-nut” hypothesis is summarized succinctly in C. Scholz, The Mechanics of Earthquakes and Faulting, Cambridge University Press, New York, pp. 340-343, 1990. 138.   M. Ohtake, T. Matumoto, and G. Latham, Seismicity gap near Oaxaca, southern Mexico, as a probable precursor to a large earthquake, Pure Appl. Geophys., 113, 375-385, 1977. Further details are given in M. Ohtake, T. Matumoto, and G. Latham, Evaluation of the forecast of the 1978 Oaxaca, southern Mexico earthquake based on a precursory seismic quiescence, in Earthquake Prediction—An International Review, D. Simpson and P. Richards, eds., American Geophysical Union, Maurice Ewing Series 4, Washington, D.C., pp. 53-62, 1981. Interpretation of the success of the prediction and the reality of the precursor is complicated by a global change in earthquake recording because some large seismic networks were closed in 1967. For more details, see R.E. Habermann, Precursory seismic quiescence: Past, present, and future, Pure Appl. Geophys., 126, 277-318, 1988. 139.   A comprehensive test requires a complete record of successes and failures for predictions made using well-defined and consistent methods. Otherwise, the likelihood of success by chance cannot be evaluated. 140.   V.I. Kieilis Borok, and V.G. Kossobokov, Premonitory activation of seismic flow: Algorithm M8, Phys. Earth Planet. Int., 61, 73-83, 1990. 141.   J.H. Healy, V.G. Kossobokov, and J.W. Dewey, A Test to Evaluate the Earthquake Prediction Algorithm M8, U.S. Geological Survey Open-File Report 92-401, Denver, Colo., 23 pp. + 6 appendixes, 1992; V.G. Kossobokov, L.L. Romashkova, V.I. Keilis-Borok, and J.H. Healy, Testing earthquake prediction algorithms: Statistically significant advance prediction of the largest earthquakes in the circum-Pacific, 1992-1997, Phys. Earth Planet. Int., 111, 187-196, 1999. 142.   See <http://www.mitp.ru/predictions.html>. A password is needed to access predictions for the current six-month time interval. 143.   John Milne noted this quest in his treatise Earthquakes and Other Earth Movements (D. Appelton and Company, New York, pp. 301 and 310, 1899): “Ever since seismology has been studied, one of the chief aims of its students has been to discover some means which could enable them to foretell the coming of an earthquake, and the attempts which have been made by workers in various countries to correlate these occurrences with other well-marked phenomena may be regarded as attempts in this direction.” Milne himself proposed short-term prediction schemes based on measurements of ground deformation and associated phenomena, such as disturbances in the local electromagnetic field. “As our knowledge of earth movements, and their attendant phenomena, increases there is little doubt that laws will be gradually formulated and in the future, as telluric disturbances increase, a large black ball gradually ascending a staff

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    may warn the inhabitants on land of a coming earthquake, with as much certainty as the ball upon a pole at many seaports warns the mariner of coming storms.” Milne’s optimism was not shared by all seismologists, notably Charles Richter, who in his textbook (C.F. Richter, Elementary Seismology, W.H. Freeman, San Francisco, pp. 385-386, 1958) dismissed short-term earthquake prediction as a “will-o’-the wisp,” questioning whether “any such prediction will be possible in the foreseeable future; the conditions of the problem are highly complex. One may compare it to the situation of a man who is bending a board across his knee and attempts to determine in advance just where and when the cracks will appear.” 144.   Ad Hoc Panel on Earthquake Prediction, Earthquake Prediction: A Proposal for a Ten Year Program of Research, White House Office of Science and Technology, Washington, D.C., 134 pp., 1965. 145.   Dilatancy is the volume expansion due to the application of a shear stress, a well-known property of granular materials. Brace and his colleagues observed this phenomenon during rock-shearing experiments in the laboratory, which they interpreted as being due to pervasive microcracking in their specimens with a concomitant increase in void space (W.R. Brace, B.W. Paulding, and C.H. Scholz, Dilatancy of the fracture of crystalline rocks, J. Geophys. Res., 71, 3939-3953, 1966). 146.   I.L. Nersesov, A.N. Semenov, and I.G. Simbireva, Space time distribution of travel time ratios of transverse and longitudinal waves in the Garm Area, in the physical basis of foreshocks, Akad. Nauk USSR, pp. 88-89, 1969. 147.   See C.H. Scholz, L.R. Sykes, and Y.P. Aggarwal, Earthquake prediction: A physical basis, Science, 181, 803-810, 1973, for a description for the laboratory and field observations that lead to the development of the dilatancy-diffusion model. 148.   For a comprehensive description of the Haicheng prediction, see P. Molnar, T. Hanks, A. Nur, B. Raleigh, F. Wu, J. Savage, C. Scholz, H. Craig, R. Turner, and G. Bennett, Prediction of the Haicheng earthquake, Eos, Trans. Am. Geophys. Union, 58, 236-272, 1977. 149.   At the time there were many articles in the popular and scientific press about the impending breakthroughs in prediction capabilities. For example, see F. Press, Earthquake prediction, Sci. Am., 232, 14-23, 1975. 150.   National Research Council, Predicting Earthquakes: A Scientific and Technical Evaluation—With Implications for Society, National Academy Press, Washington, D.C., 62 pp., 1976. 151.   C.R. Allen and D.V. Helmberger, Search for temporal changes in seismic velocities using large explosions in southern California, in Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System, R.L. Kovach and A. Nur, eds., Stanford University Publications in Geological Science 13, Stanford, Calif., pp. 436-452, 1973. 152.   J.R. Rice and J.W. Rudnicki, Earthquake precursory effects due to pore fluid stabilization of a weakening fault zone, J. Geophys. Res., 84, 2177-2193, 1979. 153.   In the reauthorization of the NEHRP program in 1990, references to earthquake prediction as a goal of the program were specifically removed. See Office of Technology Assessment, Reducing Earthquake Losses, OTA-ETI-623, U.S. Government Printing Office, Washington, D.C., 162 pp., 1995. 154.   J.H. Dieterich, Preseismic fault slip and earthquake prediction, J. Geophys. Res., 83, 3940-3948, 1978; J.R. Rice, Theory of precursory processes in the inception of earthquake rupture, Gerlands Beitr. Geophys., 88, 91-127, 1979. 155.   J.J. Lienkaemper and W.H. Prescott, Historic surface slip along the San Andreas fault near Parkfield, California, J. Geophys. Res., 94, 17,647-17,670, 1989; T. Donalee, Historical vignettes of the 1881, 1901, 1922, 1934, and 1966 Parkfield earthquakes, in Parkfield; the Prediction … and the Promise, Earthquakes and Volcanoes, 20, 52-55, 1988. 156.   Examples of current research on earthquake prediction techniques include the application of pattern recognition techniques (e.g., V.I. Keilis-Borok, L. Knopoff, I.M.

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    Rotwain, and C.R. Allen, Intermediate term prediction of occurrence time of strong earthquakes, Nature, 335, 690-694, 1988; M. Eneva, and Y. Ben-Zion, Techniques and parameters to analyze seismicity patterns associated with large earthquakes, J. Geophys. Res., 102, 17,785-17,795, 1997), investigations of geochemical precursors (e.g., H. Wakita, Geochemical challenge to earthquake prediction, Proc. Nat Acad. Sci,93, 3781-3786, 1996), and the electromagnetic techniques associated with the VAN hypothesis. This last work has generated considerable controversy (e.g., R.J. Geller, ed., Debate on “VAN,” Geophys. Res. Lett., 23, 1291-1452, 1996). For a negative assessment of the history of earthquake prediction research, see R. Geller, Earthquake prediction: A critical review, Geophys. J. Int., 131, 425-450, 1997. 157.   Western-style masonry construction had been introduced in Japan to reduce the fire hazard associated with traditional wooden structures. 158.   J. Milne and W.K. Burton, The Great Earthquake in Japan, 1891, 2nd ed., Lane, Crawford & Co., Yokohama, Japan, 69 pp + 30 plates, 1891. 159.   State Earthquake Investigation Commission, The California Earthquake of April 18, 1906, Publication 87, vol. I, Carnegie Institution of Washington, pp. 365-366, 1908. 160.   G.W. Housner, Historical view of earthquake engineering, Proceedings of the Eight World Conference on Earthquake Engineering, San Francisco, pp. 25-39, 1984. Panetti specifically proposed that the first story should be built to withstand one-twelfth of its superposed weight and the second and third stories one-eighth of their superposed weights. 161.   A. Whittaker, J Moehle, and M Higashino, Evolution of seismic design practice in Japan, Struct. Design Tall Build., 7, 93-111, 1998. 162.   The January 1927 edition of the UBC was published by the Pacific Coast Building Officials Conference. The provisions in the 1927 UBC to increase the design forces for structures on poor soils were removed in 1949, only to be reintroduced in the 1974 UBC. 163.   J.R. Freeman, Engineering data needed on earthquake motion for use in the design of earthquake-resisting structures, Bull. Seis. Soc. Am., 20, 67-87, 1930. 164.   For a discussion of the early strong-motion program, see G.W. Housner, Connections, The EERI Oral History Series, Earthquake Engineering Research Institute, Oakland, Calif., pp. 67-88, 1997; and D.E. Hudson, ed., Proc. Golden Anniversary Workshop on Strong Motion Seismometry, University of Southern California, Los Angeles, March 30-31, 1983. 165.   H. Cross, Analysis of continuous frames by distributing fixed end moments, Proc. Am. Soc. Civil Engineers, 56, 919-928, 1930; AIJ Standard for Structural Calculation of Rein-forced Concrete Structures, Kenchiku Zassh I (Architectural Institute of Japan), 47, 62 pp., 1933. 166.   M.A. Biot, A mechanical analyzer for the prediction of earthquake stresses, Bull. Seis. Soc. Am.,31, 151-171, 1940. 167.   G.W. Housner and G.D. McCann, The analysis of strong-motion earthquake records with the electric analog computer, Bull. Seis. Soc. Am.,39, 47-56, 1949. 168.   G.W. Housner, Characteristics of strong-motion earthquakes, Bull. Seis. Soc. Am., 37, 19-31, 1947. 169.   G.W. Housner, R. Martel, and J.L. Alford, Spectrum analysis of strong motion earthquakes, Bull. Seis. Soc. Am., 42, 97-120, 1953. 170.   National Research Council, The San Fernando Earthquake of February 9, 1971: Lessons from a Moderate Earthquake on the Fringe of a Densely Populated Region, National Academy Press, Washington, D.C., 24 pp., 1971. 171.   High-frequency ground motions were analyzed by D.E. Hudson (Local distribution of strong earthquake ground motions, Bull Seis. Soc. Am.,62, 1765-1786, 1972), and low-frequency motions by T.C. Hanks (Strong ground motion of the San Fernando, California earthquake: Ground displacements, Bull. Seis. Soc. Am.,65, 193-225, 1975). 172.   G.W. Housner and M.D. Trifunac, Analysis of Accelerograms—Parkfield Earthquake, Bull. Seis. Soc. Am.,57, 1193-1220, 1967.

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173.   M.D. Trifunac and D.E. Hudson, Analysis of the Pacoima Dam Accelerogram—San Fernando, California Earthquake of 1971, Bull. Seis. Soc. Am.,61, 1393-1141, 1971. 174.   T.C. Hanks and D.A. Johnson, Geophysical assessment of peak accelerations, Bull. Seis. Soc. Am.,66, 959-968, 1976. 175.   Applied Technology Council, Tentative Provisions for the Development of Seismic Regulations for Buildings, Applied Technology Council Publications ATC-3-06, Palo Alto, Calif., 505 pp., 1978. These provisions served as the basis for the seismic provisions of the 1988 Uniform Building Code and the Federal Emergency Management Agency publication, NEHRP Recommended Provisions for Seismic Regulation for New Buildings, 1994 Edition, Building Seismic Safety Council, Federal Emergency Management Agency Report FEMA-222A (Provisions, 290 pp. 15 maps, 1990) and FEMA-223A (Commentary, 335 pp., 1995), Washington, D.C. 176.   See Section 5.3.2 of Part 2—Commentary, NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, 1997 Edition, Building Seismic Safety Council, Federal Emergency Management Agency Report FEMA 303, Washington, D.C., February 1998. 177.   L. Reiter, Earthquake Hazard Analysis; Issues and Insights, Columbia University Press, New York, 233 pp., 1990. 178.   C.A. Cornell, Engineering seismic risk analysis, Bull. Seis. Soc. Am.,58, 1583-1606, 1968. 179.   E.B. Roberts and F.P. Ulrich, Seismological activities of the U.S. Coast and Geodetic Survey in 1949, Bull. Seis. Soc. Am.,41, 205-220, 1949. 180.   C.F. Richter, Seismic regionalization, Bull. Seis. Soc. Am.,49, 123-162, 1959. 181.   S.T. Algermissen and D.M. Perkins, A Probabilistic Estimate of the Maximum Ground Acceleration in Rock in the Contiguous United States, U.S. Geological Survey Open File Report 76-416, Denver, Colo., 45 pp., 1976.