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Zigone, D, Ben-Zion Y, Lehujeur M, Campillo M, Hillers G, Vernon FL.  2019.  Imaging subsurface structures in the San Jacinto fault zone with high-frequency noise recorded by dense linear arrays. Geophysical Journal International. 217:879-893.   10.1093/gji/ggz069   AbstractWebsite

Cross-correlations of 2-35 Hz ambient seismic noise recorded by three linear arrays across the San Jacinto Fault Zone (SJFZ) in Southern California are used to derive high-resolution shear wave velocity models for the top 50-90m of the crust at the array locations. Coherent Rayleigh surface waves are inverted to construct 2-D maps of group velocities in the range 0.2-0.6 km s(-1). These maps are inverted to shear wave velocities around the fault using a Markov Chain Monte Carlo approach. The results show marked low-velocity zones in the top 20-30 m with velocity reduction up to 35 per cent and shallow flower structures at depth shallower than 50 m. The derived velocities, location of low-velocity zone with respect to main surface traces and shape with depth are generally consistent with borehole measurements and previous imaging of deeper sections of the SJFZ at the same sites or nearby. The imaging technique requires only similar to 30 d of data (90 per cent of the signal-to-noise ratio is obtained in 15 d) and it bridges an observational gap between surface geology and typical tomography studies with no resolution in the top 100 m.

Ross, ZE, White MC, Vernon FL, Ben-Zion Y.  2016.  An improved algorithm for real-time S-wave picking with application to the (augmented) ANZA network in Southern California. Bulletin of the Seismological Society of America. 106:2013-2022.   10.1785/0120150230   AbstractWebsite

We develop an automatic shear-wave picking algorithm suitable for real-time applications as well as with existing databases. The method can scan through packets of continuous waveforms and make picks without prior knowledge of whether earthquakes have occurred. This makes the algorithm suitable for detecting earthquakes at the same time. Expanding upon and improving the method of Ross and Ben-Zion (2014a), the algorithm first uses polarization filters to remove P-wave energy from the seismogram. Then, short-term average/long-term average and kurtosis detectors are applied to the data in tandem to lock in on the phase arrival. The method is tested by applying it to a full month of continuous waveform data recorded by a regional network at 123 stations and comparing the resulting automatic picks with 11,353 handmade picks. The automatic picks are found to be within 0.16 s of the analyst picks 75% of the time, and S picks are successful 92% of the time that a P-wave pick is made. The algorithm is then applied to an entire year of continuous data and detects 11,197 earthquakes. The hypocenters of these earthquakes are, on average, improved by more than 1 km when compared with the regional network's automated catalog.

Jacobeit, E, Thomas C, Vernon F.  2013.  Influence of station topography and Moho depth on the mislocation vectors for the Kyrgyz Broadband Seismic Network (KNET). Geophysical Journal International. 193:949-959.   10.1093/gji/ggt014   AbstractWebsite

Deviations of slowness and backazimuth from theoretically calculated values, the so-called mislocation vectors, are measured for the Kyrgyz Broadband Seismic Network (KNET) in the Tien Shan region. 870 events have been analysed for arrivals of P and PKP waves from all azimuths. The deviations of slowness and backazimuth show a strong trend with values up to 1 s deg(-1) for slowness values for waves arriving from the North and South and backazimuth deviations of, in some cases, more than 10 degrees for waves arriving from the East and West. Calculating the traveltime deviations of the stations for topography of the Tien Shan region and Moho depth values appropriate for this area shows that most slowness and backazimuth deviations can be reduced to very small values. The remaining mislocation vectors show no strong trends and are on average smaller than 0.2 s deg(-1) for slowness and 2 degrees for backazimuth values, which is within the error bars of these measurements. Results from array methods that rely on the knowledge of the backazimuth values show much improved resolution after the correction of the mislocation vectors which shows the importance of knowing and correcting for structures directly beneath arrays.

Sales, BC, Maple MB, Vernon FL.  1978.  Initial Oxidation-Kinetics near Curie-Temperature of Nickel. Physical Review B. 18:486-491.   10.1103/PhysRevB.18.486   Website
Share, PE, Ben-Zion Y, Ross ZE, Qiu HR, Vernon FL.  2017.  Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array. Geophysical Journal International. 210:819-832.   10.1093/gji/ggx191   AbstractWebsite

Local and teleseismic earthquake waveforms recorded by a 180-m-long linear array (BB) with seven seismometers crossing the Clark fault of the San Jacinto fault zone northwest of Anza are used to image a deep bimaterial interface and core damage structure of the fault. Delay times of P waves across the array indicate an increase in slowness from the southwest most (BB01) to the northeast most (BB07) station. Automatic algorithms combined with visual inspection and additional analyses are used to identify local events generating fault zone head and trapped waves. The observed fault zone head waves imply that the Clark fault in the area is a sharp bimaterial interface, with lower seismic velocity on the southwest side. The moveout between the head and direct P arrivals for events within similar to 40 km epicentral distance indicates an average velocity contrast across the fault over that section and the top 20 km of 3.2 per cent. A constant moveout for events beyond similar to 40 km to the southeast is due to off-fault locations of these events or because the imaged deep bimaterial interface is discontinuous or ends at that distance. The lack of head waves from events beyond similar to 20 km to the northwest is associated with structural complexity near the Hemet stepover. Events located in a broad region generate fault zone trapped waves at stations BB04-BB07. Waveform inversions indicate that the most likely parameters of the trapping structure are width of similar to 200 m, S velocity reduction of 30-40 per cent with respect to the bounding blocks, Q value of 10-20 and depth of similar to 3.5 km. The trapping structure and zone with largest slowness are on the northeast side of the fault. The observed sense of velocity contrast and asymmetric damage across the fault suggest preferred rupture direction of earthquakes to the northwest. This inference is consistent with results of other geological and seismological studies.

Qiu, H, Ben-Zion Y, Ross ZE, Share PE, Vernon FL.  2017.  Internal structure of the San Jacinto fault zone at Jackass Flat from data recorded by a dense linear array. Geophysical Journal International. 209:1369-1388.   10.1093/gji/ggx096   AbstractWebsite
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Qin, L, Ben-Zion Y, Qiu H, Share PE, Ross ZE, Vernon FL.  2018.  Internal structure of the San Jacinto fault zone in the trifurcation area southeast of Anza, California, from data of dense seismic arrays. Geophysical Journal International. 213:98-114.   10.1093/gji/ggx540   AbstractWebsite

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.