Three-Dimensional Seismic Attenuation Structure around the SAFOD Site, Parkfield, California

Bennington, N. L.; Thurber, C. H.; Roecker, S. W.

doi:10.1785/0120080175

Cited by 29 publications

(31 citation statements)

References 37 publications

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“…Calculated values for coseismic changes in attenuation,

{((), Δ +1 \frac{1}{Q})}_{0}

, along each ray path, are given in Table and are of the order of 1.0 × 10 − 3 . Previous studies of time‐averaged attenuation in the Parkfield area report a P‐wave Quality factor, Q p of approximately 100–200, with lower values of 10–80 within the fault zone itself [ Abercrombie , ; Bennington et al ., ]. Given these time‐averaged Q p values, simple calculations suggest that an increase in

{((), Δ +1 \frac{1}{Q})}_{0}

of 1.0 × 10 − 3 corresponds to a decrease in Q p of the order of 10%.…”

Section: Discussionmentioning

confidence: 99%

Temporal changes in attenuation associated with the 2004 M6.0 Parkfield earthquake

et al. 2013

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Elevated seismic attenuation is often observed in fault zones due to the high degree of fracturing and fluid content. However, temporal changes in attenuation at the time of an earthquake are poorly constrained but can give indications of fracture damage and healing. In this study, spectral ratios between earthquakes within repeating clusters are calculated in an attempt to resolve temporal variations in attenuation at the time of the 2004 M6.0 Parkfield earthquake. A sharp increase in attenuation is observed immediately after the earthquake, which then decays over the next 2 years. Influences of intercluster magnitude variations, time window length and previously reported postseismic velocity changes are investigated. The postseismic decay is fit by a logarithmic function. The timescale of the decay is found to be similar to that in GPS data and ambient seismic noise velocities following the 2004 M6.0 Parkfield earthquake. The amplitude of the attenuation change corresponds to a decrease of approximately 10% in Qp at the time of the earthquake. The greatest changes are recorded on the northeast of the fault trace, consistent with preferential damage in the extensional quadrant behind a north‐westerly propagating rupture tip. Our analysis suggests that significant changes in seismic attenuation and hence fracture dilatancy during coseismic rupture are limited to depths of less than about 5 km.

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“…Calculated values for coseismic changes in attenuation,

{((), Δ +1 \frac{1}{Q})}_{0}

{((), Δ +1 \frac{1}{Q})}_{0}

of 1.0 × 10 − 3 corresponds to a decrease in Q p of the order of 10%.…”

Section: Discussionmentioning

confidence: 99%

Temporal changes in attenuation associated with the 2004 M6.0 Parkfield earthquake

et al. 2013

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“…Although the site effect parameter, S j , is usually ignored [e.g., Lees and Lindley , ; Eberhart‐Phillips and Chadwick , ], we use a joint inversion method developed by Bennington et al . [] and modified by Pesicek et al . [] that iteratively inverts the observed spectra for

Ω_{o_{ij}}

, the corner frequency

f_{i}^{c}

of each earthquake, the site response S j for each station, and

t_{ij}^{*}

by using the Levenberg‐Marquardt method [e.g., Aster et al ., ].…”

Section: Methodsmentioning

confidence: 99%

“…Here a path attenuation ( t *) estimation technique that accounts for site response [ Pesicek et al ., ], modified from Bennington et al . [], is used to analyze P waves from local earthquakes in the NMSZ. The events were recorded by the Cooperative New Madrid Seismic Network (CNMSN) and the PANDA network (Figure ).…”

Section: Introductionmentioning

confidence: 99%

High‐resolution 3‐D P wave attenuation structure of the New Madrid Seismic Zone using local earthquake tomography

et al. 2014

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A three-dimensional (3-D), high-resolution P wave seismic attenuation model for the New Madrid Seismic Zone (NMSZ) is determined using P wave path attenuation (t*) values of small-magnitude earthquakes (M D < 3.9). Events were recorded at 89 broadband and short-period seismometers of the Cooperative New Madrid Seismic Zone Network and 40 short-period seismometers of the Portable Array for Numerical Data Acquisition experiment. The amplitude spectra of all the earthquakes are simultaneously inverted for source, path (t*), and site parameters. The t* values are inverted for Q P using local earthquake tomography methods and a known 3-D P wave velocity model for the region. The four major seismicity arms of the NMSZ exhibit reduced Q P (higher attenuation) than the surrounding crust. The highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid-rich fractures along the southeast extension of the Reelfoot fault. The Q P results are consistent with previous attenuation studies in the region, which showed that active fault zones and fractured crust in the NMSZ are highly attenuating.

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“…The geophysical properties of the crust around the Parkfield region and at the SAFOD site have been characterized by a number of previous studies, including studies of seismic velocity [ Lees and Malin , 1990; Ben‐Zion and Malin , 1991; Michelini and McEvilly , 1991; Eberhart‐Phillips and Michael , 1993; Thurber et al , 2003, 2004; Roecker et al , 2004, 2006; Zhang and Thurber , 2005; Hole et al , 2006; Malin et al , 2006; Bleibinhaus et al , 2007], seismic attenuation [ Abercrombie , 2000; Bennington et al , 2008], seismic anisotropy [ Boness and Zoback , 2006; Zhang et al , 2007; Liu et al , 2008], electrical resistivity [ Unsworth et al , 1997, 2000; Unsworth and Bedrosian , 2004; Becken et al , 2008], and potential fields [ McPhee et al , 2004]. All the seismic velocity studies reported a velocity contrast across the SAF, faster to the southwest and slower to the northeast.…”

Section: Introductionmentioning

confidence: 99%

Joint inversion for Vp, Vs, and Vp/Vs at SAFOD, Parkfield, California

Zhang¹,

Thurber

Bedrosian

2009

Geochem Geophys Geosyst

129

123

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[1] We refined the three-dimensional (3-D) Vp, Vs and Vp/Vs models around the San Andreas Fault Observatory at Depth (SAFOD) site using a new double-difference (DD) seismic tomography code (tomoDDPS) that simultaneously solves for earthquake locations and all three velocity models using both absolute and differential P, S, and S-P times. This new method is able to provide a more robust Vp/Vs model than that from the original DD tomography code (tomoDD), obtained simply by dividing Vp by Vs. For the new inversion, waveform cross-correlation times for earthquakes from 2001 to 2002 were also used, in addition to arrival times from earthquakes and explosions in the region. The Vp values extracted from the model along the SAFOD trajectory match well with the borehole log data, providing in situ confirmation of our results. Similar to previous tomographic studies, the 3-D structure around Parkfield is dominated by the velocity contrast across the San Andreas Fault (SAF). In both the Vp and Vs models, there is a clear low-velocity zone as deep as 7 km along the SAF trace, compatible with the findings from fault zone guided waves. There is a high Vp/Vs anomaly zone on the southwest side of the SAF trace that is about 1-2 km wide and extends as deep as 4 km, which is interpreted to be due to fluids and fractures in the package of sedimentary rocks abutting the Salinian basement rock to the southwest. The relocated earthquakes align beneath the northeast edge of this high Vp/Vs zone. We carried out a 2-D correlation analysis for an existing resistivity model and the corresponding profiles through our model, yielding a classification that distinguishes several major lithologies.

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Three-Dimensional Seismic Attenuation Structure around the SAFOD Site, Parkfield, California

Cited by 29 publications

References 37 publications

Temporal changes in attenuation associated with the 2004 M6.0 Parkfield earthquake

Temporal changes in attenuation associated with the 2004 M6.0 Parkfield earthquake

High‐resolution 3‐D P wave attenuation structure of the New Madrid Seismic Zone using local earthquake tomography

Joint inversion for Vp, Vs, and Vp/Vs at SAFOD, Parkfield, California

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