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Earthquake Hazard Surveys
Across Urban Basins

Nevada Seismological Laboratory

NSL link
Research supported by the Clark County Dept. of Development Services, by the City of Henderson, Nevada;
and by the Southern California Earthquake Center at USC.
Prior support by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award numbers 03HQGR006D, 05HQGR0078, and 07HQGR0029. Additional research performed under the auspices of the U.S. Dept. of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. The instruments used in parts of the field program were provided by the PASSCAL facility of the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech. Data collected during those experiments will be available through the IRIS Data Management Center. The facilities of the IRIS Consortium are supported by the National Science Foundation under Cooperative Agreement EAR-0004370 and by the Department of Energy National Nuclear Security Administration.
The views and conclusions contained in this document and in linked documents are those of the authors and should not be interpreted as necessarily representing the official policies, either express or implied, of the U.S. Government.

On this page, find out about: Presentations -- Los Angeles & Las Vegas -- Reno -- Wellington, New Zealand

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Hazard Surveys in Los Angeles and Las Vegas, July 2003

PI: John Louie, 775-784-4219, louie@seismo.unr.edu
Sponsored by the National Earthquake Hazards Reduction Program, U.S. Geological Survey; and Lawrence Livermore Lab, U.S. Dept. of Energy.
Reftek RT-125 ``Texan'' recorders and field support provided by the NSF-funded IRIS/PASSCAL Instrument Center at New Mexico Tech.

Final Results from San Gabriel River, Los Angeles

LA results

Preliminary Plus Final Results from Las Vegas

LV preliminary results
Some velocity results in Las Vegas were obtained by Prof. Barbara Luke of the UNLV Civil Engineering Dept.; all work there was in collaboration with her and with Prof. Cathy Snelson and Prof. Wanda Taylor of the UNLV Dept. of Geosciences.

Objectives: These surveys of shallow ground shear velocity provide information that will assist in mitigating earthquake hazards in the Los Angeles and Las Vegas urban areas, and in responding to a damaging earthquake. This work is a reconnaissance, looking for any ``hot spots'' in the seismic shaking hazard. As shallow shear velocity decreases, shaking hazard increases.

Background: Shallow velocity is traditionally estimated with engineering surveys in boreholes. Such boreholes are costly, with results available from less than 50 sites in Los Angeles and about five sites in Las Vegas. Shaking hazard is best measured by recording damaging earthquakes on strong-motion seismometers, from which data are similarly sparse in both cities. Hazard mitigation and earthquake emergency response planning both need continuous mapping of the shaking hazard. To date these hazard maps have been predicted partly from geologic map units, but our results from Reno (below) show that existing maps may not predict shallow velocities.

Methods: Both transects were completed by UNR students using rolled arrays of IRIS/PASSCAL ``Texan'' single-channel recorders, as for the Reno transect. Data analysis was with Optim's SeisOpt® ReMiTM package, a method developed by Louie (April 2001 BSSA). Each team of 3 students placed an array of 30 (in LA) or 40 (in LV) channels spaced at 20 m for a half-hour recording period. Each channel recorded a 4.5-Hz vertical geophone. Mostly ambient seismic ``microtremor'' noise was recorded, although some arrays were supplemented with hammer blows for P-wave refraction analysis. Geophones were not buried, but were leveled carefully. With the 12-member crew, the 60-km-long San Gabriel River transect of 99 (600 m) array placements was completed in 4.5 days; the 14-km-long Las Vegas transect of 17 (800 m) array placements was completed in 2 days. Several months of permitting, preparation, and training activities preceded the July 4-16, 2003 field exercises.

Results: Preliminary estimates of 30-m depth averaged velocities, raw Rayleigh phase velocities, are plotted above. The curves are unexpectedly smooth. Results of dispersion-curve modeling will be posted here in August, and we expect modeling results to show more variance.

On this page, find out about: Presentations -- Los Angeles & Las Vegas -- Reno -- Wellington, New Zealand

Earthquake Hazard Survey in Reno

Example data files of results from:

On this page, find out about: Presentations -- Los Angeles & Las Vegas -- Reno -- Wellington, New Zealand

Shallow Vs measurements in Hutt and Wellington

In accordance with local practice, all geographic coordinates given for New Zealand use the New Zealand Geodetic Datum 1949. Conversions to other ellipsoid systems such as WGS 1984 are available from Land Information New Zealand. (In Wellington these two systems are separated by about 150 m.)
On this page, find out about: Presentations -- Los Angeles & Las Vegas -- Reno -- Wellington, New Zealand