Quantifying focal mechanism heterogeneity for fault zones in central and southern California

Bailey, I. W.; Ben‐Zion, Yehuda; Becker, T. W.; Holschneider, Matthias

doi:10.1111/j.1365-246x.2010.04745.x

Cited by 48 publications

(49 citation statements)

References 50 publications

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“…The latter is calculated assuming a faster side velocity of 5.5 km s -1 and a velocity contrast of 10 per cent based on the tomographic results of Allam & Ben-Zion (2012). We do not require polarity reversal between FZHW and direct P waves because of the mixed complex focal mechanisms for events in the region (Bailey et al 2010). Arrivals from flagged events recorded at different stations are visually compared to remove erroneous picks such as emergent early phases similar to the noise.…”

Section: Resultsmentioning

confidence: 99%

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Ben‐Zion

Ross

et al. 2017

Geophysical Journal International

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S U M M A R YLocal 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 ∼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 ∼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 ∼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 ∼200 m, S velocity reduction of 30-40 per cent with respect to the bounding blocks, Q value of 10-20 and depth of ∼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.

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Section: Resultsmentioning

confidence: 99%

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Ben‐Zion

Ross

et al. 2017

Geophysical Journal International

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“…They reported a significant change in orientation of focal mechanisms (maximum compressive stress 74° 13°relative to fault strike, compared to 62° 11°northwest and 49° 7°southeast) and suggested that this may result from stronger material within the gap. More recently, Bailey et al (2010) suggested that stress heterogeneity may be controlled by the complex-fault structures. They observed two clusters of earthquakes with primarily thrust mechanisms to the northwest and strike-slip mechanisms to the southeast of the Anza gap (Bailey et al, 2010).…”

Section: San Jacinto Fault Backgroundmentioning

confidence: 99%

“…More recently, Bailey et al (2010) suggested that stress heterogeneity may be controlled by the complex-fault structures. They observed two clusters of earthquakes with primarily thrust mechanisms to the northwest and strike-slip mechanisms to the southeast of the Anza gap (Bailey et al, 2010).…”

Section: San Jacinto Fault Backgroundmentioning

confidence: 99%

Infrequent Triggering of Tremor along the San Jacinto Fault near Anza, California

Wang¹,

Cochran²,

Agnew³

et al. 2013

Bulletin of the Seismological Society of America

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We examine the conditions necessary to trigger tremor along the San Jacinto fault (SJF) near Anza, California, where previous studies suggest triggered tremor occurs, but observations are sparse. We investigate the stress required to trigger tremor using continuous broadband seismograms from 11 stations located near Anza, California. We examine 44 M w ≥ 7:4 teleseismic events between 2001 and 2011; these events occur at a wide range of back azimuths and hypocentral distances. In addition, we included one smaller-magnitude, regional event, the 2009 M w 6.5 Gulf of California earthquake, because it induced extremely high strains at Anza. We find the only episode of triggered tremor occurred during the 3 November 2002 M w 7.8 Denali earthquake. The tremor episode lasted 300 s, was composed of 12 tremor bursts, and was located along SJF at the northwestern edge of the Anza gap at approximately 13 km depth. The tremor episode started at the Love-wave arrival, when surface-wave particle motions are primarily in the transverse direction. We find that the Denali earthquake induced the second highest stress (∼35 kPa) among the 44 teleseismic events and 1 regional event. The dominant period of the Denali surface wave was 22.8 s, at the lower end of the range observed for all events (20-40 s), similar to periods shown to trigger tremor in other locations. The surface waves from the 2009 M w 6.5 Gulf of California earthquake had the highest observed strain, yet a much shorter dominant period of 10 s and did not trigger tremor. This result suggests that not only the amplitude of the induced strain, but also the period of the incoming surface wave, may control triggering of tremors near Anza. In addition, we find that the transient-shear stress (17-35 kPa) required to trigger tremor along the SJF at Anza is distinctly higher than what has been reported for the well-studied San Andreas fault.

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“…Heterogeneous distribution of stress has been inferred within fault zones from focal mechanisms by Bailey et al . [].…”

Section: Introductionmentioning

confidence: 99%

Inversion for absolute deviatoric crustal stress using focal mechanisms and coseismic stress changes: The 2011 M9 Tohoku‐oki, Japan, earthquake

2013

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[1] The absolute magnitude of stress in the crust and the shear strength of faults are poorly known, yet fundamental quantities, in lithospheric dynamics. While stress magnitude cannot be measured directly, deviatoric stress state can be inferred indirectly from focal mechanism solutions collected before and after an earthquake. We extend a standard stress inversion for normalized stresses to invert for the 3-D spatial distribution of absolute deviatoric stress and variation of fault strength with depth using focal mechanism solutions and coseismic stress changes produced by large earthquakes. We apply the method to the 2011 M9 Tohoku-oki, Japan, earthquake. The northern Japan fore-arc crust between 5 and 15 km depths appears to be weak with fault strength of 40-90 MPa, consistent with a coefficient of friction of 0.2-0.5. The M9 Tohoku-oki coseismic stress change was large enough, relative to the ambient stress, to rotate the principal stress directions typically~20°i n the upper 20 km of the crust. The data from Japan require a heterogeneous ambient deviatoric stress field with short-wavelength (~20-50 km) fluctuations in principal stress orientations.Citation: Yang, Y.-R., K. M. Johnson, and R. Y. Chuang (2013), Inversion for absolute deviatoric crustal stress using focal mechanisms and coseismic stress changes: The 2011 M9 Tohoku-oki, Japan, earthquake,

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Quantifying focal mechanism heterogeneity for fault zones in central and southern California

Cited by 48 publications

References 50 publications

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Infrequent Triggering of Tremor along the San Jacinto Fault near Anza, California

Inversion for absolute deviatoric crustal stress using focal mechanisms and coseismic stress changes: The 2011 M9 Tohoku‐oki, Japan, earthquake

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