Velocity contrast along the Calaveras fault from analysis of fault zone head waves generated by repeating earthquakes

Abstract

[1] We systematically investigate the velocity contrast along the Calaveras fault that ruptured during the 1984 Morgan Hill earthquake using fault zone head waves (FZHW) that refract along the fault interface. We stack waveforms in 353 sets of repeating clusters, and align the peaks or troughs of the direct P waves assuming rightlateral strike-slip focal mechanisms. The obtained velocity contrasts are 2 -3% and 12-14% NW and SE of station CCO, respectively. The FZHW and the fault plane outlined by the relocated seismicity SE of CCO are more complicated than those NW of CCO. The results can be explained by a relatively simple and sharp fault interface in the NW, and a complicated fault structure with a presence of a low-velocity zone in the SE. The along-strike variations in the strength of the velocity contrast are consistent with surface geological mapping and recent 3D tomography studies in this region. Citation: Zhao, P., and Z. Peng (2008), Velocity contrast along the Calaveras fault from analysis of fault zone head waves generated by repeating earthquakes, Geophys.

Velocity contrast along the rupture zone of the 2010 Mw6.9 Yushu, China, earthquake from fault zone head waves

“…In comparison, only 1-3% velocity contrast is observed SE of the epicenter along the Jiegu segment. The obtained values of velocity contrast is similar with those observed along major plate boundary faults, ranging from 5% to 10% along the Parkfield section of the SAF (e.g., Ben-Zion and Malin, 1991; Zhao et al, 2010), 3-12% along the Calaveras Fault (e.g., Zhao and Peng, 2008), 3-8% along the Hayward Fault (e.g., Allam et al, 2014), and ∼6% along the NAF (e.g., Bulut et al, 2012). Wang et al (2013) conducted a tomographic inversion in the same region and found clear velocity contrasts extending to ∼10 km depth in the NW part of the rupture zone (i.e., Jielong segment).…”

“…(1). As was done before (e.g., Zhao and Peng, 2008;Zhao et al, 2010;Allam et al, 2014), we fit two slopes depending on whether the events occurred to the NW or SE sides of the station. Using the average P -wave velocity of 5.5 km/s (e.g., Liu et al, 2012;Wang et al, 2013), we estimate velocity contrasts at station ys02 to be ∼7.65% and ∼5.13% for events that occurred to the NW and SE sides, respectively.…”

“…These include the San Andreas Fault (SAF) at Parkfield (e.g., Ben-Zion and Malin, 1991;Zhao et al, 2010) and south of Hollister (e.g., McGuire and Ben-Zion, 2005;Lewis et al, 2007), the Calaveras Fault (e.g., Zhao and Peng, 2008) and the Hayward Fault in the Bay area (e.g., Allam et al, 2014), and the North Anatolian Fault (NAF) in northwestern Turkey (e.g., Bulut et al, 2012; * Corresponding author.…”

Internal structure of the San Jacinto fault zone at Jackass Flat from data recorded by a dense linear array

“…McGuire & Ben-Zion 2005;Zhao et al 2010;Share & Ben-Zion 2016), the North Anatolian fault in Turkey (Bulut et al 2012;Najdahmadi et al 2016) and other faults (e.g. Hough et al 1994;Zhao & Peng 2008;Yang et al 2015). FZHW also have horizontal particle motion (HPM) with a significant fault-normal component, since they are radiated from the fault, in contrast to the particle motion of the direct P wave that points in the epicentre direction (e.g.…”

Recent advances in imaging crustal fault zones: a review

“…For instance, measurements of such differential times and waveform modeling of head waves document 20 %-50 % of velocity contrast in the Bear Valley region of the SAF (McGuire and Ben-Zion 2005). Similarly, along-strike variation of velocity contrast along the Calaveras fault has also been suggested by modeling FZHW (Zhao and Peng 2008). In addition to inspecting waveforms directly, polarization analysis has been applied in automatically identifying FZHW (Allam et al 2014b).…”