|Title||Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense seismic arrays|
|Publication Type||Journal Article|
|Year of Publication||2018|
|Authors||Qin L., Ben-Zion Y., Qiu H., Share P.E, Ross Z.E, Vernon FL|
|Journal||Geophysical Journal International|
|Type of Article||Article|
|Keywords||and friction of fault zones; andreas fault; Body waves; Continental tectonics: strike-slip and; double-difference tomography; dynamic ruptures; earthquake; Earthquake dynamics; Geochemistry & Geophysics; Guided waves; guided-waves; interface; Interface waves; linear-array; rheology; structures; surface ruptures; transform; trapping structure; velocity|
We image the internal structure of the San Jacinto fault zone (SJFZ) in the trifurcation area southeast of Anza, California, with seismic records from dense linear and rectangular arrays. The examined data include recordings from more than 20 000 local earthquakes and nine teleseismic events. Automatic detection algorithms and visual inspection are used to identify P and S body waves, along with P- and S-types fault zone trapped waves (FZTW). The location at depth of the main branch of the SJFZ, the Clark fault, is identified from systematic waveform changes across lines of sensors within the dense rectangular array. Delay times of P arrivals from teleseismic and local events indicate damage asymmetry across the fault, with higher damage to the NE, producing a local reversal of the velocity contrast in the shallow crust with respect to the large-scale structure. A portion of the damage zone between the main fault and a second mapped surface trace to the NE generates P- and S-types FZTW. Inversions of high-quality S-type FZTW indicate that the most likely parameters of the trapping structure are width of similar to 70 m, S-wave velocity reduction of 60 per cent, Q value of 60 and depth of similar to 2 km. The local reversal of the shallow velocity contrast across the fault with respect to large-scale structure is consistent with preferred propagation of earthquake ruptures in the area to the NW.