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Remotely triggered earthquakes following moderate mainshocks (or, why California is not falling into the ocean) Remotely triggered earthquakes following moderate mainshocks (or, why California is not falling into the ocean)

On several occasions in recent memory California has experienced apparent clusters of earthquake activity that are too far apart to be considered related according to a classic taxonomy that includes foreshocks, mainshocks, and aftershocks. During a week-long period in July 1986, California experienced the M 6.0 North Palm Springs earthquake, the M 5.5 Oceanside earthquake, and a swarm...
Authors
Susan E. Hough

Preliminary report on the 28 September 2004, M 6.0 Parkfield, California earthquake Preliminary report on the 28 September 2004, M 6.0 Parkfield, California earthquake

The Mw 6.0 Parkfield earthquake struck central California at 17:15:14 UTC on 28 September 2004. The epicenter was located 11 km southeast of the rural town of Parkfield, adjacent to Gold Hill and on the San Andreas Fault (Figure 1). The California Integrated Seismic Network (CISN) reported that the hypocenter was located at 35.819°N, 120.364°W at a depth of 8.8 km. From the distribution...
Authors
John Langbein, Roger D. Borcherdt, Douglas Dreger, J. Fletcher, Jeanne L Hardebeck, Margaret Hellweg, C. Ji, Malcolm J. S. Johnston, Jessica R. Murray, Robert Nadeau, Michael J. Rymer, Jerome A. Treiman

An updated global earthquake catalogue for stable continental regions: Reassessing the correlation with ancient rifts An updated global earthquake catalogue for stable continental regions: Reassessing the correlation with ancient rifts

We present an updated global earthquake catalogue for stable continental regions (SCRs; i.e. intraplate earthquakes) that is available on the Internet. Our database contains information on location, magnitude, seismic moment and focal mechanisms for over 1300 M (moment magnitude) ≥ 4.5 historic and instrumentally recorded crustal events. Using this updated earthquake database in...
Authors
S.M. Schulte, Walter D. Mooney

Geodetic and seismic constraints on some seismogenic zone processes in Costa Rica Geodetic and seismic constraints on some seismogenic zone processes in Costa Rica

New seismic and geodetic data from Costa Rica provide insight into seismogenic zone processes in Central America, where the Cocos and Caribbean plates converge. Seismic data are from combined land and ocean bottom deployments in the Nicoya peninsula in northern Costa Rica and near the Osa peninsula in southern Costa Rica. In Nicoya, inversion of GPS data suggests two locked patches...
Authors
E. Norabuena, Timothy Dixon, Susan Schwartz, Heather DeShon, Andrew Newman, Marino Protti, Victor Gonzalez, LeRoy Dorman, Ernst Flueh, Paul Lundgren, Frederick Pollitz, Dan Sampson

The Loma Prieta, California, Earthquake of October 17, 1989 - Geologic setting and crustal structure The Loma Prieta, California, Earthquake of October 17, 1989 - Geologic setting and crustal structure

Although some scientists considered the Ms=7.1 Loma Prieta, Calif., earthquake of 1989 to be an anticipated event, some aspects of the earthquake were surprising. It occurred 17 km beneath the Santa Cruz Mountains along a left-stepping restraining bend in the San Andreas fault system. Rupture on the southwest-dipping fault plane consisted of subequal amounts of right-lateral and reverse...
Authors
Ray E. Wells

Using twelve years of USGS refraction lines to calibrate the Brocher and others (1997) 3D velocity model of the Bay Area Using twelve years of USGS refraction lines to calibrate the Brocher and others (1997) 3D velocity model of the Bay Area

Campbell (1983) demonstrated that site amplification correlates with depths to the 1.0, 1.5, and 2.5 km/s S-wave velocity horizons. To estimate these depths for the Bay Area stations in the PEER/NGA database, we compare the depths to the 3.2 and 4.4 km/s P-wave velocities in the Brocher and others (1997) 3D velocity model with the depths to these horizons determined from 6 refraction...
Authors
John Boatwright, Luke Blair, Rufus Catchings, Mark Goldman, Fabio Perosi, Clare Steedman

Geotechnical characterization of TriNet sites: A status report Geotechnical characterization of TriNet sites: A status report

The TriNet project, launched in 1997, created an improved, real-time seismic monitoring network in Southern California. Planning of the network began in 1995 (e.g., Heaton et al., 1996), building on the success of the earlier TERRAscope network, which included 24 digital broadband and strong-motion instruments throughout Southern California (e.g., Kanamori et al., 1993). At the end of...
Authors
John Tinsley, Susan E. Hough, Alan K. Yong, Kanamori Hiroo, Ellen Yu, V. Appel, Chris Wills

Preliminary report on the 22 December 2003, M 6.5 San Simeon, California earthquake Preliminary report on the 22 December 2003, M 6.5 San Simeon, California earthquake

The Mw 6.5 San Simeon earthquake struck the central California coast on 22 December 2003 at 19:15:56 UTC (11:15:56 am local time.) The epicenter was located 11 km northeast of the town of San Simeon, and 39 km west-northwest of Paso Robles (Figure 1), as reported by the California Integrated Seismic Network (CISN, the California region of the Advanced National Seismic System [ANSS]). The...
Authors
Jeanne L. Hardebeck, John Boatwright, D. Dreger, Rakesh Goel, V. Graizer, Kenneth W. Hudnut, Ji Chen, Lucile M. Jones, John O. Langbein, Jian Lin, Evelyn A. Roeloffs, Robert W. Simpson, K. Stark, Ross S. Stein, John Tinsley

The Catfish Lake Scarp, Allyn, Washington: Preliminary field data and implications for earthquake hazards posed by the Tacoma fault The Catfish Lake Scarp, Allyn, Washington: Preliminary field data and implications for earthquake hazards posed by the Tacoma fault

The Tacoma fault bounds gravity and aeromagnetic anomalies for 50 km across central Puget lowland from Tacoma to western Kitsap County. Tomography implies at least 6 km of post-Eocene uplift to the north of the fault relative to basinal sedimentary rocks to the south. Coastlines north of the Tacoma fault rose about 1100 years ago during a large earthquake. Abrupt uplift up to several...
Authors
Brian L. Sherrod, Alan R. Nelson, Harvey M. Kelsey, Thomas M. Brocher, Richard J. Blakely, Craig S. Weaver, Nancy K. Rountree, B. Susan Rhea, Bernard S. Jackson

The Cottage Lake aeromagnetic lineament: A possible onshore extension of the southern Whidbey Island fault, Washington The Cottage Lake aeromagnetic lineament: A possible onshore extension of the southern Whidbey Island fault, Washington

The northwest-striking southern Whidbey Island fault zone (SWIF) was mapped previously using borehole data and potential-field anomalies on Whidbey Island and marine seismic surveys beneath surrounding waterways. Abrupt subsidence at a coastal marsh on south-central Whidbey Island suggests that the SWIF experienced a MW 6.5 to 7.0 earthquake about 3000 years ago. Southeast of Whidbey...
Authors
Richard J. Blakely, Brian L. Sherrod, Ray E. Wells, Craig S. Weaver, David H. McCormack, Kathy G. Troost, Ralph A. Haugerud

Interpretation of the Seattle Uplift, Washington, as a passive-roof duplex Interpretation of the Seattle Uplift, Washington, as a passive-roof duplex

We interpret seismic lines and a wide variety of other geological and geophysical data to suggest that the Seattle uplift is a passive-roof duplex. A passive-roof duplex is bounded top and bottom by thrust faults with opposite senses of vergence that form a triangle zone at the leading edge of the advancing thrust sheet. In passive-roof duplexes the roof thrust slips only when the floor...
Authors
Thomas M. Brocher, Richard J. Blakely, Ray E. Wells
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