Quarterly Newsletter Volume 4, Number 1 Southern California Earthquake Center 3 Precarious Rocks Record Seismicity 6 Interview: Jean-Bernard Minster 12 Research in Progress: San Joaquin Hills 16 SCEC News Briefs 21 1998 SCEC Research Program and Projects 26 Feature: Charles Richter S C EE C Page 2 S C E C Southern California Earthquake Center From the Center Directors . Earth Science Research Needed for Earthquake Hazard Reduction Center Director Science Director As the science director of SCEC, I am often asked what earthquake science can do to reduce earthquake hazards and what research tasks are most important in this endeavor. The statement below addresses those questions. Comments are welcome. Please bear in mind that this statement is not meant to represent the entire SCEC research agenda. The statement addresses a practical problem—how to protect lives and property. The SCEC research agenda must address this problem while also fostering fundamental discovery that may or may not reduce hazards. Furthermore, the practical agenda below must involve national and international partnerships well beyond the SCEC boundary. —David D. Jackson ffective reduction of small and large earthquakes; have been sites of abnormally Progress requires close earthquake hazards and strain rate measurements severe effects in recent earth- cooperation between earth E requires assessment of with GPS and other techniques. quakes. However, we lack a scientists and engineers. Our the hazard, identifying options comprehensive theory that understanding suffers from A critical need is to test ideas for protecting people and explains why, and we cannot lack of specific knowledge of about earthquakes. For structures, assessing the yet distinguish well between ground motion at sites where example, the size of future effectiveness of these options, site effects and unique features damage has occurred. We have earthquakes may be limited by prioritizing mitigation, and of earthquake rupture. Some settled for overly simple readily measured quantities selling the program. First, we answers will come from descriptions of ground motion, like fault length. The earth- must attack the elements of the modeling the reverberation of such as Modified Mercalli quake potential may also be hazard that can be mitigated seismic waves in sedimentary Intensity or peak horizontal strongly affected by stresses most economically. This is basins. But we need many acceleration. Damage also from previous large earth- where the earth sciences play recordings of individual depends on the duration of quakes. We cannot adequately an essential role. Predicting earthquakes as well as record- strong shaking, its frequency test these ideas locally because times of individual earth- ings of many earthquakes at content, etc. large earthquakes are so rare. quakes does not appear individual sites to distinguish An effective strategy must possible in the foreseeable between source and site effects. To understand damage better, include international coopera- future, so an effective approach seismologists must provide a tion so that earthquakes Getting the necessary data will to risk reduction must focus on more complete description of everywhere on earth can be require new seismographs and long-term earthquake poten- motion, including a “time used to test the most important future earthquakes. We can tial. To fulfill their role, earth history” or seismogram, at sites hypotheses. accelerate our learning by scientists must answer three where damage has occurred international cooperation. important questions. What level of ground shaking, but no recordings were made— Helping to install modern i.e., interpolate readings from landslides, and liquefaction seismic arrays in Japan, New will these earthquakes cause? seismograph locations to the Where will earthquakes occur Zealand, and other hotspots locations of structures. and how large could they be? The effects of earthquake could bring us needed data An adequate solution requires shaking depend on the size Studies of active faults, records sooner. We cannot afford to new data on ground shaking and complexity of fault of past earthquakes, and waste a single earthquake. and building response. rupture, reverberation and measurements of distortion of Research is needed to develop focusing of seismic waves, and the earth’s crust help to define What is the relationship computer models of ground the local soil conditions. Earth earthquake potential. The between ground shaking and shaking, test them against scientists contribute greatly to greatest need in earthquake damage to structures? existing data, and apply them safety by identifying site hazard assessment is for basic Seismic wave trains are made to estimate the ground motion characteristics that contribute data on faults and earthquakes. complex by reverberations that caused damage. A strategy to damage, independent of the We need mapping and seismic within the crust. To develop to estimate ground motion and particulars of earthquakes. imaging of faults; fault and prioritize protective building response together will trenching to find dates and Young sedimentary sections, measures, we must know how vastly improve our ability to sizes of prehistoric earth- margins of sedimentary basins, long and how strong the waves optimize and sell an earth- quakes; seismic recordings of and other topographic features must be to cause damage. quake mitigation strategy. Southern California Earthquake Center Quarterly Newsletter, Vol. 4, No.1, 1998 Southern California Earthquake Center S C E C Page 3 Precarious Rocks May Help Estimate L.A. Basin’s Seismic Hazard By Jill Andrews from data gathered on much earthquakes in northern What’s a Precarious Rock? smaller earthquakes—and are Nevada, no delicately balanced therefore uncertain. Various rocks were found. Rock Out in the field, the initial judgment of precariousness is hazard maps for California “aprons” on steep sidehills relatively easy: the rocks look as though they could be toppled (including the SCEC “Phase II” “showed instability, including by relatively low accelerations. hazard map) depend on these mixtures of rocks with fresh In addition, they have to be in uncertain extrapolations, and surfaces that lack desert a position so that once toppled, according to Brune, there are varnish, rocks that have been they would not return to an no known field methods other flipped over with dark varnish unstable position with further than the use of precarious on the bottom and red oxide shaking. In most cases, the rocks to test these extrapola- (typical of the underside of rocks are also not the result of tions. rocks) on the top, and abun- having recently fallen dant rocks with multiple Brune’s methods for studying downslope or accidentally impact marks.” precarious rocks use observa- ending up where they are. tions of rock varnish (a dark, Ground accelerations necessary Quantitatively, the acceleration uniform finish) to assess how to topple some precarious required to topple a rock is long they have been in place. rocks can be estimated with roughly proportional to the Rock varnish, combined with stability calculations, force tests tangent of the angle between local geomorphic evidence, can in the field, and artificially vertical and a line from the help establish the approximate induced ground motion. In center of mass to the base length of time precarious rocks addition, studies of areas of rocking point, multiplied by have been in their present recent high ground motion the acceleration of gravity positions. For example, in a further calibrate the methods (Wiechert, 1994). study he conducted in the (Brune, 1992). A statistical vicinity of known historic study of a number of rocks is ames Brune’s 1998 SCEC- percent the force of gravity) or funded research project, less. Significant damage to About the researcher: James N. Brune is director of the Seismo- J“Study of the Toppling older buildings begins at this logical Laboratory at the Mackay School of Mines and professor of geophysics in the Department of Geological Sciences at the Accelerations of Precarious level. University of Nevada, Reno, a SCEC core institution. Brune is Rocks on a Profile Perpendicu- For comparison, the Southern the recipient of numerous honors and awards, including the 1997 lar to the San Andreas Fault for California Earthquake Center Seismological Society of America Medal, an award given for sci- Constraining Strong Motion produced a hazard map entific contributions that bolster the overall field of earthquake Attenuation Relationships for showing the number of times science and engineering. Great Earthquakes,” is an per century the shaking from innovative approach to earthquakes will exceed 20 When presenting the medal to Brune, Ralph Archuleta, president earthquake hazard assessment. percent the force of gravity. of SSA, pointed out that Jim’s mentors, colleagues, and students His studies of precariously Cast in probability terms, the have “universally commented on his deep intuitive approach to balanced rocks may provide same analysis predicts that the addressing fundamental problems. Phrases such as ’extraordi- important quantitative greater southern California nary intuitive sense,’ ’incredible strength of intuition and sharp- constraints on ground motion region should experience a ness of reasoning,’ and ’remarkable physical insight’ are used to from large earthquakes in the magnitude 7.0 or greater describe his approach to science.” last few thousand years (also earthquake