HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Full Text (PDF) Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Johnston, M. J. S. Articles by Gladwin, M. T. Search for Related Content GeoRef GeoRef Citation

Continuous Borehole Strain and Pore Pressure in the Near Field of the 28 September 2004 M 6.0 Parkfield, California, Earthquake: Implications for Nucleation, Fault Response, Earthquake Prediction, and Tremor

¹ U.S. Geological Survey
345 Middlefield Road, MS977
Menlo Park, California 94025
 (M.J.S.J., R.D.B.)
² Department of Terrestrial Magnetism
Carnegie Institution of Washington
5241 Broad Branch Road NW
Washington, DC 20015
 (A.T.L.)
³ GTSM Technologies
Brisbane, 4069
Australia
 (M.G.)

Near-field observations of high-precision borehole strain and pore pressure, show no indication of coherent accelerating strain or pore pressure during the weeks to seconds before the 28 September 2004 M 6.0 Parkfield earthquake. Minor changes in strain rate did occur at a few sites during the last 24 hr before the earthquake but these changes are neither significant nor have the form expected for strain during slip coalescence initiating fault failure. Seconds before the event, strain is stable at the 10^–11 level. Final prerupture nucleation slip in the hypocentral region is constrained to have a moment less than 2 x 10¹² N m (M 2.2) and a source size less than 30 m. Ground displacement data indicate similar constraints. Localized rupture nucleation and runaway precludes useful prediction of damaging earthquakes. Coseismic dynamic strains of about 10 microstrain peak-to-peak were superimposed on volumetric strain offsets of about 0.5 microstrain to the northwest of the epicenter and about 0.2 microstrain to the southeast of the epicenter, consistent with right lateral slip. Observed strain and Global Positioning System (GPS) offsets can be simply fit with 20 cm of slip between 4 and 10 km on a 20-km segment of the fault north of Gold Hill (M₀ = 7 x 10¹⁷ N m). Variable slip inversion models using GPS data and seismic data indicate similar moments. Observed postseismic strain is 60% to 300% of the coseismic strain, indicating incomplete release of accumulated strain. No measurable change in fault zone compliance preceding or following the earthquake is indicated by stable earth tidal response. No indications of strain change accompany nonvolcanic tremor events reported prior to and following the earthquake.

This article has been cited by other articles:

				R. A. Harris and J R. Arrowsmith Introduction to the Special Issue on the 2004 Parkfield Earthquake and the Parkfield Earthquake Prediction Experiment Bulletin of the Seismological Society of America, September 1, 2006; 96(4B): S1 - S10. [Abstract] [Full Text] [PDF]

				R. D. Borcherdt, M. J. S. Johnston, G. Glassmoyer, and C. Dietel Recordings of the 2004 Parkfield Earthquake on the General Earthquake Observation System Array: Implications for Earthquake Precursors, Fault Rupture, and Coseismic Strain Changes Bulletin of the Seismological Society of America, September 1, 2006; 96(4B): S73 - S89. [Abstract] [Full Text] [PDF]

				J. Langbein, J. R. Murray, and H. A. Snyder Coseismic and Initial Postseismic Deformation from the 2004 Parkfield, California, Earthquake, Observed by Global Positioning System, Electronic Distance Meter, Creepmeters, and Borehole Strainmeters Bulletin of the Seismological Society of America, September 1, 2006; 96(4B): S304 - S320. [Abstract] [Full Text] [PDF]