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

2006/09/01 by M. J. S. Johnston · 1 voice · 7 citations
Earth and Planetary Sciences · #Earthquake Detection and Analysis #High-pressure geophysics and materials #earthquake and tectonic studies

paper · doi:10.1785/0120050822

openalex publication_date 2006/09/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/22

Abstract

Near-field observations of high-precision borehole strain and pore pres- sure, 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 earth- quake 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 � 10 12 Nm( 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 (M 0 � 7 � 10 17 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.

Citations

• Slip on the San Andreas Fault at Parkfield, California, over Two Earthquake Cycles, and the Implications for Seismic Hazard
• Coseismic and Initial Postseismic Deformation from the 2004 Parkfield, California, Earthquake, Observed by Global Positioning System, Electronic Distance Meter, Creepmeters, and Borehole Strainmeters
• Recordings of the 2004 Parkfield Earthquake on the General Earthquake Observation System Array: Implications for Earthquake Precursors, Fault Rupture, and Coseismic Strain Changes
• Kinematic Inversion of the 2004 M 6.0 Parkfield Earthquake Including an Approximation to Site Effects

Cited by

• Coseismic and Initial Postseismic Deformation from the 2004 Parkfield, California, Earthquake, Observed by Global Positioning System, Electronic Distance Meter, Creepmeters, and Borehole Strainmeters
• Recordings of the 2004 Parkfield Earthquake on the General Earthquake Observation System Array: Implications for Earthquake Precursors, Fault Rupture, and Coseismic Strain Changes
• Seismicity of Algeria from 1365 to 2013: Maximum Observed Intensity Map (MOI2014)
• Non-volcanic Tremor: A Window into the Roots of Fault Zones
• OPERATIONAL EARTHQUAKE FORECASTING. State of Knowledge and Guidelines for Utilization
• Coupling between mineral reactions, chemical changes in groundwater, and earthquakes in Iceland
• The 2004 Parkfield earthquake: Test of the electromagnetic precursor hypothesis

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