Open AccessRobust features of the source process for the 2004 Parkfield, California, earthquake from strong‐motion seismograms
Author(s) -
Twardzik C.,
Madariaga R.,
Das S.,
Custódio S.
Publication year - 2012
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2012.05653.x
Subject(s) - seismology , geology , aftershock , seismogram , slip (aerodynamics) , asperity (geotechnical engineering) , hypocenter , geodesy , seismic moment , ellipse , earthquake rupture , amplitude , geometry , fault (geology) , induced seismicity , geotechnical engineering , physics , quantum mechanics , thermodynamics , mathematics
SUMMARY We explore a recently developed procedure for kinematic inversion based on an elliptical subfault approximation. In this method, the slip is modelled by a small set of elliptical patches, each ellipse having a Gaussian distribution of slip. We invert near‐field strong ground motion for the 2004 September 28 M w 6.0 Parkfield, California, earthquake. The data set consists of 10 digital three‐component 18‐s long displacement seismograms. The best model gives a moment of 1.21 × 10 18 N m, with slip on two distinct ellipses, one with a high‐slip amplitude of 0.91 m located 20 km northwest of the hypocentre. The average rupture speed of the rupture process is ∼2.7 km s −1 . We find no slip in the top 5 km. At this depth, a lineation of small aftershocks marks the transition from creeping above to locked below, in the interseismic period. The high‐slip patch coincides spatially with the hypocentre of the 1966 M w 6.0 Parkfield, California, earthquake. The larger earthquakes prior to the 2004 Parkfield earthquake and the aftershocks of the 2004 earthquake ( M w > 3) also lie around this high‐slip patch, where our model images a sharp slip gradient. This observation suggests the presence of a permanent asperity that breaks during large earthquakes, and has important implications for the slip deficit observed on the Parkfield segment, which is necessary for reliable seismic hazard assessment.