Living on an Active Earth Perspectives on Earthquake Science (2003) / Chapter Skim
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2. The Rise of Earthquake Science
2. The Rise of Earthquake Science
Pages 19-106
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From page 19... ...
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.
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For example, in 31 B.C. a strong earthquake devastated fudea, and the historian Tosephus 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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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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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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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.
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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.
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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~.
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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 id that depends linearly on the effective normal stress Anew acting across that plane: Tc = T0 + P(Tn Of, (2.1)
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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.
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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.
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RISE OF EARTHQUAKE SCIENCE 29 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.
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Today all of these propositions are accepted with only minor modifications (18~. Although some geologists, for at least the latter half of the nineteenth century, had considered the notion that most large earthquakes result from fault slippage, Reid's hypothesis was boldly revolutionary.
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S and L waves by plotting their travel times as a function of distance for earthquakes whose location had been fixed by local observations.
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Improved locations meant that seismologists could use the travel time of the seismic waves to develop better models of the variations of wave velocities with depth, which in turn could be used to improve the location of the earthquake's initial radiation (hypocenter) , as well as its origin time.
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During the next decade, Richter and Gutenberg refined and extended the methodology to include earthquakes recorded by various instrument types and at teleseismic distances. Gutenberg published a series of papers in 1945 detailing the construction of magnitude scales based on the maximum amplitude of long-period surface waves (Ms)
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By 1959, the reliable identification of small underground nuclear explosions had become the primary technical issue confronting the verification of a comprehensive nuclear test ban treaty, and the resulting U.S. program in nuclear explosion seismology, Project Vela Uniform, motivated important developments in earthquake science (34~.
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nearly all intermediate and deep seismicity is associated with planar zones that dip beneath volcanic island arcs and arc-like orogenic (mountain-building) structures; and (3)
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Later workers used Chinnery's model to provide a physical model for Reid's elastic rebound theory, arguing that the deformation before the 1906 earthquake was due to nearly steady slip at depth on the San Andreas fault, while the shallow part of the fault slipped enough in the earthquake itself to catch up, at least approximately, with the lower fault surface. 2.4 PLATE TECTONICS Alfred Wegener, a German meteorologist, first put forward his theory of continental drift in 1912 (44~.
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Each of these source types is a specialization of the seismic moment tensor M SOURCE: Modified from B.R.
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Within the next 10 years, the key elements of plate tectonics were put in place. The main conceptual breakthrough was the recognition that on a global scale, the amount of new basaltic crust generated by seafloor spreading the bilateral separation of the seafloor along the mid-ocean ridge axis is balanced by subduction the thrusting of basaltic crust into the mantle at the oceanic trenches.
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, but even larger displacements greater than 1000 kilometers could be inferred from the offsets of magnetic anomalies observed across fracture zones in the Pacific Ocean (51~. In a 1965 paper that laid out the basic ideas of the plate theory, the Canadian geophysicist T
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While the system of oceanic ridges and transform faults fit neatly together in seafloor spreading, the compressional arcs and mountain belts juxtaposed all types of active faulting, which continued to baffle geologists. Benioff had pointed out the asymmetric polarity of the island arcs, correctly proposing that the deep oceanic trenches are surface expressions of giant reverse faults (59~.
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41 'A A rt ~ .s >` ~ ~ c ~ to ~ ~ o ~ 2: red ~ red ~,rE ~51~,'.
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Dan McKenzie and Robert Parker took the next major step toward completion of the plate theory in 1967, when they showed that slip vectors from Stauder's mechanisms of Alaskan earthquakes could be combined with the azimuth of the San Andreas fault to compute a consistent pole of instantaneous rotation for the Pacific and North American plates (67~. At the same time, lason Morgan's analysis of seafloor spreading rates and transform-fault azimuths demonstrated the global consistency of plate kinematics (68~.
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From page 43... ...
Similar differences were observed for transform faults; in the oceans, the active slip is confined to very narrow zones, in marked contrast to the broad belts of continental strike-slip tectonics, which often involve many distributed, interdependent fault systems. For example, only about two-thirds of the relative motion between the Pacific and North American plates turned out to be accommodated along the infamous San Andreas fault; the remainder is taken up on subsidiary faults and by oblique extension in the Basin and Range Province (see Section 3.2~.
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was grounded in the kinematical principles of plate tectonics (73) , and her paper did much to convince geologists that the new theory was a useful framework for understanding the complexities of continental tectonics.
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Much of the early work on convergent plate boundaries interpreted mountain building in terms of two-dimensional models that consider deformations only in the vertical planes perpendicular to the strikes of the convergent zones. During a protracted continent-continent collision, however, crustal material is eventually squeezed sideways out of the collision zone along lateral systems of strike-slip faults.
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From page 47... ...
Although earthquakes surely involve some nonelastic, volumetric effects such as fluid flow, cracking of new rock, and the expansion of gouge zones, Gilbert and Reid's idealization still forms the conceptual framework for much of earthquake science, both basic and applied. Nevertheless, because the friction mechanism was not obviously compatible with deep earthquakes, as described below, their view that earthquakes are frictional instabilities on faults had, by the time Wilson wrote his 1965 paper on plate tectonics, been considered and rejected by some scientists.
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From page 48... ...
This implies that the stress drops during crustal earthquakes could be much smaller than the rock strength, eliminating the major seismological discrepancy. Subsequent experiments at the Massachusetts Institute of Technology found a transition from stick-slip behavior to ductile creep at about 350°C (85~.
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Many subsequent studies have demonstrated a consistent relationship between seismic moment and the various magnitude scales developed from the Richter standard; the results can be expressed as a general moment magnitude Mw of the form Mw = 3 (log Me - 9 05) (Me in newton-meters)
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26, 2001 Bhuj, India 8.0 7.6 340 NOTE: All events are shallow except Bolivia, which had a focal depth of 657 km. Moment magnitude MW computed from seismic moment Me via Equation 2.7.
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Substituting this relationship into Equation 2.6 yields Moo /\`r~ A3/2. A logarithmic plot of seismic moment Me versus fault area A for a representative sample of crustal earthquakes on plate boundaries shows scatter about a linear relationship with a slope of about 1.5, implying that the stress drop is approximately constant across a large range of earthquake sizes, with an average value close to 3 megapascals (Figure 2.11)
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Note that measurements of the static stress drop vary as the cube of the corner frequency, a sensitivity that contributes to substantial scatter in /\`r for individual events. The value cited is based on a numerical study of rupture dynamics (R.
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Attempts to measure a heat flow anomaly on the San Andreas fault found no evidence of a peak (111~. The puzzle of fault stress levels was further complicated as data became available in the middle to late 1980s on principal stress orientations in the crust near the San Andreas (112~; the maximum stress direction was found to be steeply inclined to the fault trace and to re
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2.6 EARTHQUAKE PREDICTION Earthquake prediction is commonly defined as specifying the location, magnitude, and time of an impending earthquake within specified ranges. Earthquake predictions are customarily classified into long term (decades to centuries)
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This interval can be estimated either from known dates of past characteristic earthquakes or from D/V, the ratio of the average slip in a characteristic quake to the long-term slip rate on the fault. A seismic gap is a fault segment that has not ruptured in a characteristic earthquake for a time longer than T
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For example, characteristic earthquakes can be counted confidently, and their average recurrence time would be an important measure of seismic hazard. The time of the last one would start a seismic clock, by which the probability of another such earthquake could be estimated.
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57 .` ._ o ~ - o, a, ~ CO ° a, .~ ~ o o Cat o o ~ o o o A be o .s ~ ~ 't .Q ~ au ~ V)
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Shimazaki and Nakata found that the Holocene uplift data for several wellstudied sites in lapan were consistent with a time-predictable model of the largest events. Japanese seismologists and geologists have long been at the forefront of earthquake prediction studies, and their government has sponsored the world's largest and best-funded research programs on earthquake phenomena (129~.
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Many seismologists now agree that accurate forecasts are difficult even for plate boundaries such as this one that have seemingly regular historical sequences of earthquakes.
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Moderate earthquakes of about M 6 on the San Andreas fault near Parkfield were recorded instrumentally in 1922, 1934, and 1966, and pre-instrumental data revealed that similar-size earthquakes occurred in 1857, 1881, and 1901. The regular recurrence of Parkfield events at an average interval of about 22-years and the similarity of the foreshock pattern in 1934 and 1966 led to the hypothesis that these events were characteristic earthquakes, breaking the same segment of the San Andreas with about the same slip.
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From page 61... ...
In some regions near a ruptured fault segment, the stress is actually increased, offering an explanation for seismic clustering. At present, the model offers a good retrospective explanation for many earthquake sequences, but it has not been implemented as a testable prediction hypotheses because the stress pattern depends on details of the previous rupture, fault geometry, stress-strain properties of the crust, possible fluid flow in response to earthquake stress increments, and other properties that are very difficult to measure in sufficient detail.
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In the year following the destructive 1964 Alaskan earthquake, a select committee of the White House Office of Science and Technology issued a report called Earthquake Prediction: A Proposal for a Ten Year Program of Research, which called for a national program of research focused on this goal (144~. Optimism about the feasibility of short-term prediction was heightened in the mid-1970s by the apparent successes of empirical prediction schemes and the plausibility of physical process models, such as dilatancy diffusion.
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Reproduced by permission of American Geophysical Union. lion science.
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and on qualitative field observations prior to an M 6 earthquake on the San Andreas fault near Parkfield, California (155~. The preseismic slip observed under laboratory conditions was very subtle, but theoretical calculations suggested that under favorable conditions it might be observable in the field, provided that the critical slip distance DC observed in the lab studies scaled to a larger size on natural faults.
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Research continues on a broad range of proposed techniques for short-term prediction, as does vigorous debate on its promise (156~. Most seismologists now agree that the difficulties of earthquake prediction were previously underestimated and that basic understanding of the earthquake process must precede prediction.
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For building foundations on soft soil in earthquake-prone regions, the UBC's optional provisions corresponded to a lateral force coefficient equal to the Japanese value. Measurement of Strong Ground Motions By 1930, networks of permanent seismic observatories allowed the location and analysis of large earthquakes anywhere on the globe.
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From page 67... ...
They began to record strong ground motions using longperiod seismometers with little or no magnification, and by the 1930s, the development of broader-band, triggered devices allowed accurate measurement of the waves most destructive to buildings, those with shorter period and therefore higher acceleration. The Long Beach earthquake of 1933 was the first large event to be recorded by these improved strongmotion seismometers, several of which had been installed in the Los Angeles region just nine months before the earthquake.
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For the next 25 years, this was the largest measured ground acceleration, establishing the E1 Centro record as the de facto standard for earthquake engineering in the United States and Japan (Figure 2.17~. Response Spectra for Structural Analysis Both the Long Beach and the E1 Centro data influenced the development of seismic safety provisions in building codes.
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From page 69... ...
Seed and I.M. Idriss, Ground Motions and Soil Liquefaction During Earthquakes, Earthquake Engineering Research Institute, Engineering Monograph on Earthquake Criteria, Structural Design, and Strong Motion Records 5, E1 Cerrito, Calif., 134 pp., 1982.
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Computing response spectra over a wide range of frequencies using data from a wide range of earthquakes significantly improved understanding of the damage potential of strong motion. Building Code Improvements Since 1950 The availability of strong-motion data began to transform earthquake engineering from a practice based on pseudostatic force criteria to a science grounded in an understanding of the complex coupling between ground motions and building vibrations.
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The uncertainties in the empirical coefficients remained high, but the form of the lateral force requirement did establish a firm connection between strong-motion measurements and the requirements of earthquake engineering. The dearth of strong-motion data ended when the San Fernando earthquake (M 6.6)
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After the 1971 San Fernando earthquake, policy makers tried to update building codes in light of the large amount of data on ground motion
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At shorter periods, this expression was replaced by a limiting value proportional to the effective peak acceleration coefficient Aa. The report also provides the first contoured maps of the ground-motion parameters Aa and Av, derived from a probabilistic seismic hazard analysis conducted by the USGS.
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From page 74... ...
Eventually, response spectra were computed directly from ground-motion attenuation relationships. Seismic Hazard Analysis By the 1960s, growing strong-motion databases and scientific understanding enabled site-specific seismic hazard assessments incorporating information about the length and distance of neighboring faults, the history of seismicity, and empirical predictions of ground-motion intensity for events of specified magnitude at specified distances.
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From page 75... ...
Seed and I.M. Idriss, Ground Motions and Soil Liquefaction During Earthquakes, Earthquake Engineering Research Institute, Engineering Monograph on Earthquake Criteria, Structural Design, and Strong Motion Records 5, E1 Cerrito, Calif., 134 pp., 1982.
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From page 76... ...
Seed and I.M. Idriss, Ground Motions and Soil Liquefaction During Earthquakes, Earthquake Engineering Research Institute, Engineering Monograph on Earthquake Criteria, Structural Design, and Strong Motion Records 5, E1 Cerrito, Calif., 134 pp., 1982.
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and for variance about the predicted ground motions due to natural variability. The final result for a site is a hazard curve, a plot of mean annual frequency of exceedance at a specified intensity level.
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Ho~lanba~g Mu 0 ~ 0 ~ 5- ~ au au can vet au ~ au .X ° as 5 C/)
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From page 79... ...
The USGS updated the national seismic hazard maps in 1982, 1990, 1991, 1994, and 1996, incorporating new knowledge on earthquake sources and seismicwave propagation. The 1991 maps were the first to display probabilistic values of response spectral ordinates and were published in the NEHRP Recommended Provisions for Seismic Regulationsfor New Buildings.
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From page 80... ...
Challenges Ahead Establishing building codes, developing attenuation relationships and performing seismic hazard analysis are all examples of earthquake engineering activities that have helped quantify and reduce the threat posed by earthquakes; however, recent large earthquakes make it clear that significant challenges remain. For example, the 1995 Hyogo-ken Nanbu earthquake (Box 2.5, Figures 2.22 and 2.23)
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From page 81... ...
Sekiguchi, Three-dimensional simulation of the near-fault ground motion for the 1995 Hyogo-ken Nanbu (Kobe) , Japan, earthquake, Bull.
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The First Principles of Observational Seismology, Chapman and Hall, London, 2 vole., 831 pp., 1862. He also introduced the term hypocenter for the focus of the earthquake, which he presumed was a volcanic explosion, and deduced its location from the observed directions of ground motions, assumed to be excited by pure compressional waves.
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16. The State Earthquake Investigation Commission reports on the 1906 earthquake have been the principal source of data for the study of strong ground motions by D.M.
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430~; he considered the role of fault friction in the generation of slip irregularities that cause strong ground motions (pp.
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applied the GaussNewton method to the iterative, least-squares solution of the nonlinear equations relating the space-time location parameters to the arrival times of seismic waves, and in the 1930s, Jeffreys showed how the least-squares normal equations could be solved efficiently by successive approximations. The first implementations of Geiger's method on electronic computers was in 1960 (B.
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From page 88... ...
The active element in the standard instrument was a copper mass suspended vertically on a torsion spring with a free period of 0.8 second whose rotation was magnetically attenuated (damping constant of 0.8) and photographically recorded by a light beam reflected from a mirror mounted on the mass; the apparatus was sensitive only to horizontal ground motions, which it recorded with a nominal static magnification of 2800.
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in 1961. Between 1960 and 1971, about $245 million were expended by Vela Uniform, the underground explosion component of Project Vela.
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From page 90... ...
Honda and his colleagues in Japan who plotted the initial motions and amplitudes of both P and S waves on the focal sphere; they showed that the S-wave patterns for deep Japanese earthquakes were not consistent with singlecouple mechanisms, which required an S-wave node in the plane of faulting, but rather with double couples, which did not (H. Honda, Earthquake mechanism and seismic waves, J
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49. Reprints of the original papers and historical commentaries on the confirmation of seafloor spreading by marine magnetic data can be found in Plate Tectonics and Geomagnetic Reversals by A
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Macdonald and H Kuno, eds., American Geophysical Union Monograph 6, Washington, D.C., pp.
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64. The first arrival times of seismic waves at stations around the world demonstrated that the focus was shallow, but the closest recording seismograph was at College, Alaska440 kilometers from the epicenter so that seismologists were unable to fix the depth to the nucleation point precisely enough to help the geologists.
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From page 94... ...
Res., 73, 36613697,1968) reconstruction of the Mesozoic and Cenozoic history of seafloor spreading and continental drift in terms of finite rotations constrained by magnetic anomaly data.
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From page 95... ...
Recent studies have demonstrated that almost all deep-focus earthquakes can be explained with a simple planar fault model with stress drops ranging from 10 bar to 1 kilobar (e.g., H Kawakatsu, Insignificant isotropic component in the moment tensor of deep earthquakes, Nature, 351, 50-53, 1991~.
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From page 96... ...
Weeks, Constitutive behavior and stability of frictional sliding of granite, Pure Appl. Geophys., 124, 1042, 1986; N.M.
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Rice, Constitutive relations for fault slip and earthquake instabilities, Pure Appl. Geophys., 121, 443475, 1983~.
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From page 98... ...
Hanks (Earthquake stress drops, ambient tectonic stresses and stresses that drive plate motions, Pure Appl. Geophys., 115, 441-458, 1977~.
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From page 99... ...
. 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.
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From page 100... ...
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.
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Coppersmith, Fault behavior and characteristic earthquakes: Examples from the Wasatch and San Andreas faults, J Geophys.
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From page 102... ...
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 eventspecific, "practical earthquake prediction." The program involves six agencies, with the scientific lead given to the Japan Meteorological Agency.
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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
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J.H. Dieterich, Preseismic fault slip and earthquake prediction, J
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Lett., 23, 1291-1452, 1996~. For a negative assessment of the history of earthquake prediction research, see R
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From page 106... ...
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)
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