Earthquake Repeat Time and Average Stress Drop Hiroo Kanamori, Hiroo Kanamori Seismological Laboratory, California Institute of Technology, Pasadena, California 91125Search for more papers by this authorClarence R. Allen, Clarence R. Allen Seismological Laboratory, California Institute of Technology, Pasadena, California 91125Search for more papers by this author Hiroo Kanamori, Hiroo Kanamori Seismological Laboratory, California Institute of Technology, Pasadena, California 91125Search for more papers by this authorClarence R. Allen, Clarence R. Allen Seismological Laboratory, California Institute of Technology, Pasadena, California 91125Search for more papers by this author Book Editor(s):Shamita Das, Shamita DasSearch for more papers by this authorJohn Boatwright, John BoatwrightSearch for more papers by this authorChristopher H. Scholz, Christopher H. ScholzSearch for more papers by this author First published: 01 January 1986 https://doi.org/10.1029/GM037p0227Citations: 76Book Series:Geophysical Monograph Series AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Summary Existing data on source parameters of large crustal earthquakes (subduction events are not considered here) over a wide range of repeat times indicate that, for a given magnitude (Ms or MW), earthquakes with long repeat times have shorter fault lengths than those with short repeat times. A shorter fault length for a given magnitude indicates a larger average stress drop which reflects the average strength of the fault zone. Our result therefore suggests that faults with longer repeat times are stronger than those with shorter repeat times. In terms of an asperity model in which the average strength of a fault zone is determined by the ratio, ra, of the total area of the asperities (strong spots on a fault plane) to the total area of the fault zone, the above result suggests that ra is proportional to the repeat time. Our result provides a method to estimate seismic source spectra from the fault length and the repeat time of a potential causative fault. Citing Literature Earthquake Source Mechanics, Volume 37 RelatedInformation

Robert Phillip Sharp, one of the leading figures of American geology, died peacefully in his home in Santa Barbara, California, on 25 May 2004. Bob’s enormous contributions on the physical processes that have modified the surfaces of Earth and Mars are scientific classics that have substantially enhanced our understanding of the unique roles of water, wind, and ice in modifying planetary surfaces. Virtually an equal contribution was Bob’s vision and leadership in geological academia, primarily at Caltech.Bob was born in Oxnard, California, on 24 June 1911. As an undergraduate at Caltech in the 1930s, he was quarterback of the football team in his senior year and an outstanding student. He chose to do his doctoral work at Harvard University and prepared a thesis, under Kirk Bryan, on the geology of the Ruby–East Humboldt Range area of northeastern Nevada, where his discovery of Pleistocene glacial landforms in the summit area sparked an interest in glaciers and glaciation that persisted throughout his career. He also participated in a two-month geological expedition boating down the Grand Canyon, the inner gorge of which was, at the time, essentially terra incognita in terms of its geology. Jobs were scarce in 1938, when Bob obtained his doctorate, and he felt lucky to land an academic position at the University of Illinois. He was called into military service with the US Army Air Corps five years later and researched and wrote survival manuals for downed fliers in the North Pacific–Alaska region. His personal survival experiences in the westernmost Aleutians and on the slopes of Mt. McKinley further stimulated his interest in a variety of geological topics, particularly glaciology. After a brief postwar period at the University of Minnesota, he returned in 1947 to Caltech, where he spent the remainder of his academic career. His teaching was legendary, particularly his introductory geology course. On nomination by a group of undergraduates, he was named by Life magazine in 1950 as one of the top 10 US college teachers of the year. In 1952, he was appointed chairman of the division of geological sciences and, during the ensuing 16 years, played a central role in building Caltech into a leader in innovative efforts in geochemistry and planetary science. In his research, Bob embarked on a major drilling program on the Malaspina Glacier in southeastern Alaska in an attempt to better understand the physics of glacier flow. He subsequently shifted that effort to the Blue Glacier on Mt. Olympus in northwest Washington. His collaboration with geochemist Sam Epstein led to pioneering efforts in climate change. Bob also studied the role of wind as a geological agent; his work on dune formation is particularly well known. Around 1961, another important chapter in his scientific career began with attempts to understand geological surface processes on Mars. Bob and Caltech colleagues formed the team to evaluate the Mariner TV imaging of Mars and contributed to the recognition of the role water played in Martian evolution, still a central theme in our growing understanding of that planet.Bob’s leadership at Caltech was punctuated by two major developments. The first was the phasing out of the vertebrate paleontology program and a major thrust, supported by Linus Pauling and others, into the emerging area of geochemistry. Many classical geology colleagues around the country, who literally accused Caltech of “selling out” geology to the geochemists, initially did not look favorably on the new emphasis on geochemistry. However, they subsequently recognized it as a forward-looking and daring move. The second new thrust in the 1960s required a choice between ocean-floor geophysics and planetary science. The presence in Pasadena of the Jet Propulsion Laboratory was a strong argument in favor of planetary science, and Bob even received the blessing of the Caltech astronomers, who were deeply engrossed in far-out space and were quite willing to “give away” our solar system to the geologists. Numerous national honors were bestowed on Bob during his career. But the two in which he took the most pride were the 1977 Penrose Medal of the Geological Society of America—its highest honor—and NSF’s National Medal of Science, presented to him in 1989. When awarded the Penrose Medal, he commented that “few scientists in other professional fields seem to enjoy and savor their work as fully as do Earth scientists.” If there was one activity Bob enjoyed above all, it was the planning and leading of geological field trips for students, alumni, and others. Those included yearly trips to Hawaii for graduating students.It is an intriguing enigma that Bob, with his profoundly rigid self-discipline and basically conservative ways, would nevertheless leave a lasting legacy of truly forward-looking innovation in his scientific and academic ventures. He is remembered so fondly by a multitude of friends from all walks of life as an immensely warm and generous individual. Robert Phillip Sharp PPT|High resolution© 2005 American Institute of Physics.

Research Article| November 01, 1998 Evidence for Unusually Strong Near-field Ground Motion on the Hanging Wall of the San Fernando Fault during the 1971 Earthquake Clarence R. Allen; Clarence R. Allen Seismological Laboratory California Institute of Technology Pasadena, California (C.R.A.) Search for other works by this author on: GSW Google Scholar James N. Brune; James N. Brune Seismological Laboratory University of Nevada Reno, Nevada (J.N.B.) Search for other works by this author on: GSW Google Scholar Lloyd S. Cluff; Lloyd S. Cluff Pacific Gas and Electric Company San Francisco, California (L.S.C.) Search for other works by this author on: GSW Google Scholar Allan G. Barrows, Jr. Allan G. Barrows, Jr. California Division of Mines and Geology Los Angeles, California (A. G.B.) Search for other works by this author on: GSW Google Scholar Author and Article Information Clarence R. Allen Seismological Laboratory California Institute of Technology Pasadena, California (C.R.A.) James N. Brune Seismological Laboratory University of Nevada Reno, Nevada (J.N.B.) Lloyd S. Cluff Pacific Gas and Electric Company San Francisco, California (L.S.C.) Allan G. Barrows, Jr. California Division of Mines and Geology Los Angeles, California (A. G.B.) Publisher: Seismological Society of America First Online: 09 Mar 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 1998 by the Seismological Society of America Seismological Research Letters (1998) 69 (6): 524–531. https://doi.org/10.1785/gssrl.69.6.524 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Clarence R. Allen, James N. Brune, Lloyd S. Cluff, Allan G. Barrows; Evidence for Unusually Strong Near-field Ground Motion on the Hanging Wall of the San Fernando Fault during the 1971 Earthquake. Seismological Research Letters 1998;; 69 (6): 524–531. doi: https://doi.org/10.1785/gssrl.69.6.524 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

This may be an historic event for many of you. It will be the first time that you have ever heard a geologist give a talk related to earthquakes that was not replete with Kodachrome slides of cracks in the ground and maps of active faults, or at least of allegedly active faults, or potentially active faults or even possibly active faults! But I would like to go beyond the detailed discussion of individual earthquakes this afternoon, and instead discuss the broader problem of whether our studies of numerous recent earthquakes -- here and abroad -- are leading to modifications in our hazard assessment techniques, speaking from the point of view of a geologist or seismologist. I emphasize that I make no pretext of speaking for either the geotechnical or structural engineers. You already know, of course, the answer posed by the title. It's both yes and no. And I would like to focus on the question of: In what scientific areas, in particular, are our approaches changing, and in what areas do the traditional methods remain credible?

The Xianshuihe fault of western Sichuan Province, China, is one of the world's most active faults, having produced 4 earthquakes during this century of magnitude greater-than-or-equal-to 7 along a 350-km length of the fault. At least 8 such events have occurred since 1725. In the more limited 150-km-long segment including Luhuo and Daofu, major earthquakes in 1904, 1923, 1973, and 1981 (M = 7, 7 1/2, 7.6, 6.9) were associated with overlapping surficial fault ruptures and with individual left-lateral displacements as large as 3.6 m. Field studies indicate that this high degree of activity is typical of the fault's longer-term history. The Holocene left-lateral slip rate on the northwestern segment of the fault has been 15 +/- 5 mm/yr, decreasing to about 5 mm/yr on its southeastern segment, based on radiometrically dated offset stream-channel and terrace deposits and on offset glacial moraines.Physiographic features of active faulting are fully as diagrammatic as those of California's San Andreas fault, mainly because of high-altitude preservation and the absence of cultural modification on this eastern margin of the Tibetan Plateau. Detailed en echelon tensional and pushup features resulting from surface ruptures in 1973, 1955, 1923, and 1893 can still be recognized today, and new data have been collected bearing on the offsets and fault-rupture lengths during these and other events.The locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the Xianshuihe fault. Obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events, whereas segmentation control for others remains obscure. Based on the historic record, repeat times estimated from slip rates, and current seismic gaps, two segments are particularly likely sites for M = 7+ earthquakes in the near future: the 65-km-long segment between Daofu and Qianning, and the 135-km-long segment bracketing Kangding. Continuing creep has been documented along some segments of the fault, and this, together with the high degree of activity and other unique attributes, makes the Xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard-evaluation studies.

This proposed plan for the southern San Andreas fault, with ongoing earthquake hazard assessment and communication of any inferred increases in hazard, has

On 24 November 1987, two significant earthquakes occurred along the southern San Jacinto fault zone and related structural elements in southern California, not far from the International Border. These two events, the Elmore Ranch earthquake (M = 6.2 at 0154 GMT) and the Superstition Hills earthquake (M = 6.6 at 1315 GMT, both moment magnitudes from Sipkin, 1989), and their aftershocks have yielded a rich harvest of geological, seismological, and engineering data pertinent to the cause and effect of earthquakes in this region, where the southern San Jacinto fault zone enters the Salton Depression from the Peninsula Ranges bordering it on the southwest (Fig. 1). This special issue of the Bulletin presents 18 geologic and seismologic investigations of these earthquakes, a collection of papers born in El Centro, California, on 8 and 9 February 1988 at a meeting attended by approximately 60 scientists interested in these earthquakes for one reason or another.

Pattern recognition procedures for infrequent events are adapted to the problem of identifying patterns of clustering of small- and intermediate-scale seismicity before large earthquakes. Identification procedures derived from analysis of large California and Nevada earthquakes yield a high success rate when applied to other parts of the world.

Obituary| December 01, 1987 Charles F. Richter: A personal tribute* Clarence R. Allen Clarence R. Allen Seismological Laboratory California Institute of TechnologyPasadena, California 91125 Search for other works by this author on: GSW Google Scholar Author and Article Information Clarence R. Allen Seismological Laboratory California Institute of TechnologyPasadena, California 91125 Publisher: Seismological Society of America First Online: 03 Mar 2017 Online Issn: 1943-3573 Print Issn: 0037-1106 Copyright © 1987, by the Seismological Society of America Bulletin of the Seismological Society of America (1987) 77 (6): 2234–2237. https://doi.org/10.1785/BSSA0770062234 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Clarence R. Allen; Charles F. Richter: A personal tribute. Bulletin of the Seismological Society of America 1987;; 77 (6): 2234–2237. doi: https://doi.org/10.1785/BSSA0770062234 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A 500-m section of the Palm Spring Formation in the southern Mecca Hills, located within the San Andreas fault zone in southeastern California, has been paleomagnetically sampled to determine possible tectonic rotation in this area and to establish time-stratigraphic control. This work was partly stimulated by the fact that 80 km farther south, previous studies demonstrated 35° of postdepositional rotation in the Palm Spring Formation of the Vallecito-Fish Creek basin east of the Elsinore fault. Several lines of evidence suggest that hematite is the main magnetic carrier of the Mecca Hills samples. Large anhedral hematite grains observed in magnetic extracts and a positive fold test imply a detrital origin of the remanence. The polarity reversal patterns, together with earlier vertebrate paleontologic studies, restrict the time span for deposition of this unit to the middle-late Matuyama chron (2.0–0.75 myr ago), thus of uppermost Pliocene and early Pleistocene age. Characteristic directions of best least-squares fit for 73 samples suggest little or no overall rotation, despite the severe late Quaternary tectonic activity demonstrated by the intense deformation of these strata.

AbstractThe Garlock fault is a 265-km-long left-slip fault striking northeastward from the San Andreas fault in southern California. Relocations of earthquakes that occurred from 1932 to 1981 on and near this major fault were made using the master-event technique. The spatial distribution of seismicity along the fault is different west and east of its midpoint near Rand, where the largest en-echelon offset and a marked change in strike occur. These two segments also display distinct geologic features and different seismic and aseismic behavior. The 150-km-long segment west of Rand has shown continuous low seismic activity during the past 50 yr, well-documented aseismic creep, and has a relatively complex fault trace. In contrast, the 155-km-long segment east of Rand has very few small earthquakes, no demonstrable creep, and a simpler fault trace. P-wave first-motion studies substantiate predominantly left-slip motion along the Garlock fault. Overall energy release during this 50-yr period gives a seismic moment rate of 2.75 × 1021 dyne-cm/yr, much lower than that inferred from Holocene geologic offsets, thus indicating that the Garlock fault currently represents a temporal seismic gap, and that the potential exists for large earthquakes. If behavior of the Garlock fault is similar to that of the San Andreas, the western segment of the fault can be compared with the central creeping segment of the San Andreas, and the eastern segment with those segments broken by the 1857 and 1906 earthquakes; thus larger events might be expected on the eastern segment than on the western segment, or, if the entire fault breaks during a single event, larger displacements toward the east.

The source processes of the 4 January 1970, Tonghai earthquake (Ms = 7.5) and the 6 February 1973, Luhuo earthquake (Ms = 7.5) in southwestern China were investigated using an inversion technique on the very complex body waves. The two earthquakes were associated with 48 and 90 km of surficial strike-slip rupture, respectively, and the distribution of displacement with distance along the fault was well documented by field studies of both events. The source process for both earthquakes comprised three to four subevents with different moments and rupture durations. These calculated parameters agree well with the field observations and aftershock distributions, particularly in the total rupture length and in the amount and asymmetry of fault displacements relative to the locations of the main epicenters.

The North Anatolian fault of Turkey is remarkably similar to the San Andreas fault of California in its style of displacement, high seismicity, physiographic expression, neotectonic history, presence of creep, and problems of seismic-hazard evaluation. On the other hand, significant contrasts between the two faults exist in their space-time patterns of seismicity and in their plate-tectonic relationships. Workers in the two areas have much to learn from one another.