Depth extent of damage zones around the central Calaveras fault from waveform analysis of repeating earthquakes

Abstract

S U M M A R YWe systematically investigate spatial variations of temporal changes and depth extent of damage zones along the Calaveras fault that ruptured during the 1984 Morgan Hill earthquake by the waveform analysis of 333 sets of repeating earthquakes. We use a sliding window waveform cross-correlation technique to measure traveltime changes in waveforms generated by each repeating cluster. We find clear traveltime delays in the S-and early S-coda waves for events immediately after the Morgan Hill main shock. The amplitudes of the time delays decrease logarithmically with time since the main shock, indicating a time-dependent recovery (healing) process following the abrupt coseismic temporal changes. The largest temporal changes are observed at station CCO that is the closest to the rupture zone of the Morgan Hill main shock. The time delays at this station are larger for clusters in the top 6 km, and decrease systematically at larger depth. In comparison, the time delays observed at other five stations are much smaller, and do not show clear relationship with hypocentral depth. We suggest that the temporal changes at these five stations mostly occur in the top few hundred metres of the near-surface layers, while the temporal changes at station CCO are likely associated with the damage zone around the Calaveras fault that is well developed in the top few kilometres of the upper crust. Our results are consistent with the inference of a widespread damage and non-linearity in the near-surface layers associated with strong ground motions of nearby large earthquakes, and localized damages and flower-type structures around active faults based on previous studies of fault zone structures and recent 3-D numerical simulations.

Fault-zone healing effectiveness and the structural evolution of strike-slip fault systems

“…The overall geometry of the ‘flower‐like’ damage zones in our simulations is compatible with field observations (e.g. Sylvester 1988; Rockwell & Ben‐Zion 2007; Zhao & Peng 2009) and with numerical simulations of off‐fault deformation (e.g. Ma 2008).…”

“…Karabulut & Bouchon 2007; Wu et al . 2009; Zhao & Peng 2009). To update the constraints on healing parameters we use recent fault zone observations from the ECSZ (Cochran et al .…”

Variability of fault slip behavior along the San Andreas Fault in the San Juan Bautista Region

“…We identify a pair of earthquakes as CREs if both the cross‐correlation coefficient and the phase coherency are greater than 0.95, for at least two stations (Figure ), to reduce the chance of false CRE detections. Our cross‐correlation and coherency thresholds are comparable to those used in previous studies [ Zhao and Peng , ; Shirzaei et al ., ; Turner et al ., ]. Two seismograms that exceed these thresholds are identified as pairs of repeating earthquakes.…”

Spatiotemporal variations of characteristic repeating earthquake sequences along the Middle America Trench in Mexico

“…Previous studies have identified repeating earthquakes in a large variety of tectonic environments including California [ Vidale et al , ] Japan [ Uchida et al , ; Matsuzawa et al , ; Kimura et al , ], China [ Schaff and Richards , ], Taiwan [ Chen et al , , ], Turkey [ Peng and Ben‐Zion , ], and Tonga‐Vanuatu [ Yu , ]. Here repeating earthquakes have been observed along the creeping segment of the San Andreas Fault [ Nadeau and Johnson , ; Schaff et al , ; Rubin et al , ; Taira et al , ] and along the Calaveras fault [ Vidale et al , ; Marone et al , ; Schaff and Beroza , ; Peng et al , ; Zhao and Peng , ; Templeton et al , ]. Characteristic repeating sequences in these environments have been exploited as a common framework to explore the physical mechanism behind their origin and occurrence [ Sammis and Rice , ; Beeler et al , ].…”