High-resolution imaging of the Bear Valley section of the San Andreas fault at seismogenic depths with fault-zone head waves and relocated seismicity

McGuire, J. J.; Ben‐Zion, Yehuda

doi:10.1111/j.1365-246x.2005.02703.x

Cited by 93 publications

(106 citation statements)

References 68 publications

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“…9). This contrast is not as large as across the San Andreas fault south of Hollister (McGuire & Ben-Zion 2005), but is comparable to values obtained for the San Andreas fault around San Gorgonio Pass , Hayward fault (Allam et al 2014b) and North Anatolian fault (Najdahmadi et al 2016). The obtained value reflects an average velocity contrast over the top 20 km of the crust.…”

Section: Discussionsupporting

confidence: 62%

“…FZHW provide the highest resolution tool for imaging the existence and properties of bimaterial fault interfaces (e.g. Ben-Zion et al 1992;McGuire & Ben-Zion 2005). On the other hand, misidentification of FZHW as direct arrivals can introduce biases and errors into derived velocity structures, earthquake locations and fault plane solutions (e.g.…”

Section: Introductionmentioning

confidence: 99%

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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: Discussionsupporting

confidence: 62%

Section: Introductionmentioning

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 used waveform cross-correlation to obtain precise relative locations for nearly 5000 magnitude 1 -3 earthquakes distributed over 60 km of the San Andreas fault near San Juan Bautista. As at Parkfield, lower velocity rocks here lie to the NE [Eberhart-Phillips and Michael, 1998;Rubin, 2002a;McGuire and Ben-Zion, 2005], so the expected direction of preferred propagation for subshear ruptures is to the SE. Roughly 300 of the microearthquakes had aftershocks that occurred within 10 hours and roughly 2 mainshock radii of the mainshock centroid.…”

Section: Introductionmentioning

confidence: 99%

“…A more targeted approach for determining the contrast is from the move-out of head waves, relative to the direct P-wave arrivals, as seen by stations near the fault on the side with the lower wave speed. McGuire and Ben-Zion [2005] made such measurements for earthquakes within the Bear Valley section of the San Andreas fault, within a few kilometers of much of the region contributing to our catalogue. They obtained P-wave velocity contrasts in two locations, each averaged over $5 km along the fault, of 20% and 35%.…”

Section: Reasonable Velocity Contrastsmentioning

confidence: 99%

Aftershock asymmetry on a bimaterial interface

2007

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[1] To better understand the asymmetric distribution of microearthquake aftershocks along the central San Andreas fault, we study dynamic models of slip-weakening ruptures on an interface separating differing elastic half-spaces. Subshear ruptures grow as slightly asymmetric bilateral cracks, with larger propagation velocities, slip velocities, and normal stress changes at the rupture front moving in the direction of slip of the medium with the lower shear wave speed (the southeast front, in the context of the San Andreas). When the SE front encounters a stress barrier, the tensile stress perturbation behind the rupture front continues forward and for a wide range of barrier strengths nucleates a dying slip pulse. This slip pulse smooths the stress field and reduces the static stress change beyond the SE front. Furthermore, because the tensile stress that carried the slip pulse into the barrier is a purely dynamic phenomenon, the SE rupture front can be left far below the failure threshold, while the NW front remains quite close to failure. Both mechanisms could contribute to the observed aftershock asymmetry. Formation of a robust slip pulse requires a peak tensile stress perturbation that approaches the nominal strength drop of the slip-weakening law. To achieve this while minimizing off-fault damage requires either substantial velocity contrasts or small reductions in friction. The simulations also show a pronounced asymmetry in the timescales over which barriers to the SE and NW experience increasing stresses, a result that has implications for the asymmetric distribution of subevents in compound earthquakes.

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“…In places with good network coverage and relocated seismicity, the width of such zones is only a few tens of meters (e.g., POUPINET et al, 1984;NADEAU et al, 1994;SCHAFF et al, 2002;MCGUIRE and BEN-ZION, 2005;THURBER et al, 2006). A significant deviation from the relatively simple DZ structure described above occurs at fault stepover zones.…”

Section: Geological and Geophysical Observations Of Fault Zone Structurementioning

confidence: 99%

Structural Properties and Deformation Patterns of Evolving Strike-slip Faults: Numerical Simulations Incorporating Damage Rheology

Finzi

Hearn

Ben‐Zion

et al. 2009

Mechanics, Structure and Evolution of Fault Zones

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Abstract-We present results on evolving geometrical and material properties of large strike-slip fault zones and associated deformation fields, using 3-D numerical simulations in a rheologically-layered model with a seismogenic upper crust governed by a continuum brittle damage framework over a viscoelastic substrate. The damage healing parameters we employ are constrained using results of test models and geophysical observations of healing along active faults. The model simulations exhibit several results that are likely to have general applicability. The fault zones form initially as complex segmented structures and evolve overall with continuing deformation toward contiguous, simpler structures. Along relatively-straight mature segments, the models produce flower structures with depth consisting of a broad damage zone in the top few kilometers of the crust and highly localized damage at depth. The flower structures form during an early evolutionary stage of the fault system (before a total offset of about 0.05 to 0.1 km has accumulated), and persist as continued deformation localizes further along narrow slip zones. The tectonic strain at seismogenic depths is concentrated along the highly damaged cores of the main fault zones, although at shallow depths a small portion of the strain is accommodated over a broader region. This broader domain corresponds to shallow damage (or compliant) zones which have been identified in several seismic and geodetic studies of active faults. The models produce releasing stepovers between fault zone segments that are locations of ongoing interseismic deformation. Material within the fault stepovers remains damaged during the entire earthquake cycle (with significantly reduced rigidity and shearwave velocity) to depths of 10 to 15 km. These persistent damage zones should be detectable by geophysical imaging studies and could have important implications for earthquake dynamics and seismic hazard.

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High-resolution imaging of the Bear Valley section of the San Andreas fault at seismogenic depths with fault-zone head waves and relocated seismicity

Cited by 93 publications

References 68 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

Aftershock asymmetry on a bimaterial interface

Structural Properties and Deformation Patterns of Evolving Strike-slip Faults: Numerical Simulations Incorporating Damage Rheology

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