Distribution of aseismic slip rate on the Hayward fault inferred from seismic and geodetic data

Abstract

[1] We solve for the slip rate distribution on the Hayward fault by performing a least squares inversion of geodetic and seismic data sets. Our analysis focuses on the northern 60 km of the fault. Interferometric synthetic aperture radar (InSAR) data from 13 independent ERS interferograms are stacked to obtain range change rates from 1992 to 2000. Horizontal surface displacement rates at 141 bench marks are measured using GPS from 1994 to 2003. Surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion. The fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface. South of the city of Hayward, a steeply, east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth. The inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of $5 mm/yr to a depth of 4-6 km. The interferometric synthetic aperture radar (InSAR) data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath Point Pinole, although the InSAR data might be complicated by a small dip-slip component at this location. A low slip rate patch of <1 mm/yr is inferred beneath San Leandro consistent with the source location of the 1868 earthquake. We calculate that the entire fault is accumulating a slip rate deficit equivalent to a M w = 6.77 ± 0.05 per century. However, this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip.

Behavior of Repeating Earthquake Sequences in Central California and the Implications for Subsurface Fault Creep

“…Determining the distribution of displacement over these actively creeping fault planes can be aided by the ability to calculate slip at specific points at depth on a fault from RE seismic data. This information can complement slip results from geodetic measurements of surface deformation (Schmidt et al, 2005). Additionally, since surface geodetic measurements can have difficulty resolving slip in the mid-to lower seismogenic zone (Bos and Spakmann, 2003), even areas with excellent surface geodetic data could benefit from RE data points which can extend down to the bottom of the seismogenic zone.…”

Implications of recent asperity failures and aseismic creep for time-dependent earthquake hazard on the Hayward fault

“…Given the empirical probability that 82 earthquakes in California have a ~5% chance to be foreshocks of subsequent larger events 83 within several days (Reasenberg and Jones, 1989), and the location of the events close to the 84 main locked zone of the HF at depth (Schmidt et al, 2005), the multiple felt events caused 85 concern both in the local communities and among researchers. 86…”

Rupture process for micro-earthquakes inferred from borehole seismic recordings

“…Crustal deformation along the HF is characterized by a wide variety of fault slip behaviors from aseismic creep (Schmidt et al 2005) to stick-slip earthquakes including the 1868 HF earthquake that had an inferred seismic moment magnitude (M w ) of 6.8 (e.g., Lienkaemper et al 2012). To explore the rupture processes for the four target earthquakes (Table 1), we make use of borehole seismograms from the Hayward fault network (HFN).…”