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2012), Computing a large refined catalog of focal mechanisms for Southern California (1981–2010): Temporal stability of the style of faulting
 Bulletin of the Seismological Society of America
"... termed the HASH method, we calculate focal mechanisms for earthquakes that occurred in the southern California region from 1981 to 2010. When available, we use hypocenters refined with differential travel times from waveform cross correlation. Using both the Pwave first motion polarities and the S/ ..."
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termed the HASH method, we calculate focal mechanisms for earthquakes that occurred in the southern California region from 1981 to 2010. When available, we use hypocenters refined with differential travel times from waveform cross correlation. Using both the Pwave first motion polarities and the S/P amplitude ratios computed from threecomponent seismograms, we determine mechanisms for more than 480,000 earthquakes and analyze the statistical features of the whole catalog. We filter the preliminary catalog with criteria associated with mean nodal plane uncertainty and azimuthal gap and obtain a highquality catalog with approximately 179,000 focal mechanisms. As more S/P amplitude ratios become available after 2000, the average nodal plane uncertainty decreases significantly compared with mechanisms that include only Pwave polarities. In general the parameters of the focal mechanisms have been stable during the three decades. The dominant style of faulting is high angle strikeslip faulting with the most likely P axis centered at N5°E. For earthquakes of M <2:5, there are more normalfaulting events than reversefaulting events, while the opposite holds forM>2:5 events. Using the 210 momenttensor solutions in Tape et al. (2010) as benchmarks, we compare the focal plane rotation angles of common events in the catalog. Seventy percent of common earthquakes match well with rotation angles less than the typical nodal plane uncertainty. The common events with relatively large rotation angles are either located around the edge of the (SCSN) network or poorly recorded. Online Material: Table of HASH parameter settings and figures of 1D velocity models, distribution of earthquakes with different focalmechanism qualities, comparison of YHS2010 and HS2003 catalogs, and distributions of earthquake focal mechanisms.
Threedimensional seismic velocity structure and precise earthquake relocations in the Salton trough
, 2013
"... Abstract I present a new 3D seismic velocity model and highprecision earthquake ..."
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Abstract I present a new 3D seismic velocity model and highprecision earthquake
FullWave Seismic Data Assimilation: Theoretical Background and Recent Advances
"... Abstract—The seismological inverse problem has much in common with the data assimilation problem found in meteorology and oceanography. Using the data assimilation methodology, I will formulate the seismological inverse problem for estimating seismic source and Earth structure parameters in the form ..."
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Abstract—The seismological inverse problem has much in common with the data assimilation problem found in meteorology and oceanography. Using the data assimilation methodology, I will formulate the seismological inverse problem for estimating seismic source and Earth structure parameters in the form of weakconstraint generalized inverse, in which the seismic wave equation and the associated initial and boundary conditions are allowed to contain errors. The resulting Euler–Lagrange equations are closely related to the adjoint method and the scatteringintegral method, which have been successfully applied in full3D, fullwave seismic tomography and earthquake source parameter inversions. I will review some recent applications of the fullwave methodology in seismic tomography and seismic source parameter inversions and discuss some challenging issues related to the computational implementation and the effective exploitation of seismic waveform data. 1.
Apparent anisotropy in inhomogeneous isotropic media, Geophys
 J. Int
, 2011
"... Surface waves propagating through a laterally inhomogeneous medium undergo wavefield complications such as multiple scattering, wavefront healing, and backward scattering. Unless accounted for accurately, these effects will introduce a systematic isotropic bias in estimates of azimuthal anisotropy. ..."
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Surface waves propagating through a laterally inhomogeneous medium undergo wavefield complications such as multiple scattering, wavefront healing, and backward scattering. Unless accounted for accurately, these effects will introduce a systematic isotropic bias in estimates of azimuthal anisotropy. We demonstrate with synthetic experiments that backward scattering near an observing station will introduce an apparent 360 ° periodicity into the azimuthal distribution of anisotropy near strong lateral variations in seismic wave speeds that increases with period. Because it violates reciprocity, this apparent 1ψ anisotropy, where ψ is the azimuthal angle, is nonphysical and is, therefore, a useful indicator of isotropic bias. Isotropic bias of the 2ψ (180° periodicity) component of azimuthal anisotropy, in contrast, is caused mainly by wavefront healing, which results from the broad forward scattering part of the surface wave sensitivity kernel. To test these predictions, we apply geometrical ray theoretic (eikonal) tomography to teleseismic Rayleigh wave measurements across the Transportable Array component of USArray to measure the directional dependence of phase velocities between 30 and 80 second period. Eikonal tomography accounts for multiple scattering (ray bending) but not finite frequency
Waveform Inversion for OneDimensional NearSurface Structure in the New Madrid Seismic Zone 107
, 2009
"... Abstract Waveform inversion is applied to P and S waveforms selected from microearthquakes of duration magnitude (Md) between 1.8 and 2.4 recorded at station PARM in Stahl Farm, Missouri, operated by the Cooperative New Madrid Seismic Network in the upper Mississippi Embayment to resolve the onedim ..."
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Abstract Waveform inversion is applied to P and S waveforms selected from microearthquakes of duration magnitude (Md) between 1.8 and 2.4 recorded at station PARM in Stahl Farm, Missouri, operated by the Cooperative New Madrid Seismic Network in the upper Mississippi Embayment to resolve the onedimensional (1D) velocity structure of uppermost nearsurface soils. Constrained by vertical seismic profiling (VSP) and standard cone penetration test (SCPT) data at nearby sites, we begin by defining a gradient velocity structure in the soils. A reference velocity model is constructed by grid search in which the observed P and PS wave shapes, PPS travel time, and P=PS amplitude ratio are the controlling factors in the systematic selection from among 136,000 models. A waveform inverse scheme is then implemented to obtain the least spectral misfit and best waveform correlation between synthetic and observed data. Four simultaneous inversions of joint waveforms from P and S wave types are performed. Resolved four 1D final models with associated uncertainties are listed in this article. The uppermost 7 m of nearsurface soil exhibit very low velocities, through which VP and VS are in the ranges of 140 m=s to 470 m=s and 95 m=s to 215 m=s, respectively. This noninvasive technique demonstrates that the observed highfrequency reverberations (1–17 Hz) of P, S, and PS waveforms from local microearthquakes can be utilized to provide a view of the nearsurface soil structure. Although there are tradeoffs between layer thickness and slowness, this method explains much of the highfrequency site response due to microearthquake wave propagation through the very lowvelocity, nearsurface soils.
ⒺSpectralElement Simulations of Seismic Waves Generated by the 2009 L’Aquila Earthquake
"... Abstract We adopt a spectralelement method (SEM) to perform numerical simulations of the complex wavefield generated by the 6 April 2009 Mw 6.3 L’Aquila earthquake in central Italy. The mainshock is represented by a finitefault solution obtained by inverting strongmotion and Global Positioning S ..."
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Abstract We adopt a spectralelement method (SEM) to perform numerical simulations of the complex wavefield generated by the 6 April 2009 Mw 6.3 L’Aquila earthquake in central Italy. The mainshock is represented by a finitefault solution obtained by inverting strongmotion and Global Positioning System data, testing both 1D and 3D wavespeed models for central Italy. Surface topography, attenuation, and the Moho discontinuity are also accommodated. Including these complexities is essential to accurately simulate seismicwave propagation. Threecomponent synthetic waveforms are compared to corresponding velocimeter and strongmotion recordings. The results show a favorable match between data and synthetics up to ∼0:5 Hz in a 200 km × 200 km × 60 km model volume, capturing features mainly related to topography or lowwavespeed basins. We construct synthetic peak ground velocity maps that, for the 3D model, are in good agreement with observations, thus providing valuable information for seismichazard assessment. Exploiting the SEM in combination with an adjoint method, we calculate finitefrequency kernels for specific seismic arrivals. These kernels capture the volumetric sensitivity associated with the selected waveform and highlight prominent effects of topography on seismicwave propagation in central Italy. Online Material: Movie of wave propagation, waveform fits, and stable of station parameters.
structure beneath Central America
, 2014
"... ei sm ol og y Methods for inversion of bodywave waveforms for localized threedimensional seismic structure and an application to D′′ ..."
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ei sm ol og y Methods for inversion of bodywave waveforms for localized threedimensional seismic structure and an application to D′′
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"... ei sm ol og y Empirically determined finite frequency sensitivity kernels for surface waves ..."
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ei sm ol og y Empirically determined finite frequency sensitivity kernels for surface waves