The determination of source parameters for small earthquakes from a single, very broadband seismic station

Fan, Guangwei; Wallace, Terry C.

doi:10.1029/91gl01804

Cited by 69 publications

(45 citation statements)

References 10 publications

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“…With the development of modern broadband instruments and the success in modeling broadband records, Dreger and Helmberger (1993) had demonstrated the feasibility of retrieving stable source orientations using long period body waves (mainly Pnl and Sn) from a couple of pioneer broadband stations in southern California. Their work paralleled that of Fan and Wallace (1991) in New Mexico. Surface waves also prove useful in source mechanism determination as demonstrated by several authors addressing different periods (e.g., Thio and Kanamori, 1995, 10-50 s;Romanowicz et al, 1993, 15-50 s; Ritsma and Lay, 1993, > 50 s), although the methods using surface waves alone require some azimuthal sampling around the source.…”

Section: Introductionmentioning

confidence: 82%

Surface Wave Path Corrections and Source Inversions in Southern California

Tan

Song

Wei

et al. 2010

Bulletin of the Seismological Society of America

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The cut-and-paste (CAP) method for retrieving earthquake source parameters has proven useful in many regions. Since CAP breaks three-component data into Pnl and surface wave segments and models them separately, imperfect 1D Green's functions can be effectively used to model the records and determine source parameters. The resultant time shifts for different segments, for example, Pnl or surface waves, can provide valuable data for improving the velocity model or Green's functions. Moreover, if these shifts can be known from empirical path calibrations or estimated from a tomographic map, we can recover both source mechanism and location with an extended procedure CAPloc . Here we present a complete workflow from path calibration to source inversion in southern California. In particular, we use the CAP results from about 160 events with known locations to derive the Rayleigh and Love wave group velocity maps. We take a tomographic approach to solve for lateral velocity variations in 10 km size cells in a uniformly 12 km thick seismogenic layer. Velocity variations of up to 15% are observed and the patterns correlate well with some geological features. Synthetic surface waves for 2D cuts throughout the model with a finite difference approach show significant improvement over 1D synthetics in fitting surface wave travel times, but little difference in waveforms, which suggests 1D synthetics are sufficient in modeling with simple time shifts. This simplification allows source inversion for both mechanism and location to be easily obtained with CAPloc. Finally, we test the effectiveness of CAPloc in determining source parameters, including both mechanisms and locations with such calibration maps in poorly monitored situations. In particular, we focus on two station inversions with two pioneer stations PAS and GSC, which have appropriate recordings since 1960. Considerable success is achieved when the events are bracketed.

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Section: Introductionmentioning

confidence: 82%

Surface Wave Path Corrections and Source Inversions in Southern California

Tan

Song

Wei

et al. 2010

Bulletin of the Seismological Society of America

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“…For regional distances, it is also possible to obtain the SMT of intermediate-magnitude earthquakes (less than M 5.5) using one station by using simple but well calibrated velocity models (Dreger and Helmberger, 1991;Fan and Wallace, 1991;Walter, 1993). For earthquakes of larger magnitudes, however, the effects of source directivity should be compensated for by the use of multiple stations.…”

Section: Near-real-time Seismic Moment-tensor Calculationsmentioning

confidence: 99%

Near-real-time Seismic Moment-tensor Determination in Spain

Rueda¹,

Mézcua²

2005

Seismological Research Letters

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“…The propagation paths are short, thus signi®cantly aected by unknown small-scale crustal heterogeneities. This calls for methods based on low frequencies (e.g., FAN and WALLACE, 1991;JONES et al, 1993), however weak events are not very rich in them. Thus the selection of a proper instrument and an appropriate frequency window is critical.…”

Section: Introductionmentioning

confidence: 99%

Focal Mechanisms of Weak Earthquakes from Amplitude Spectra and Polarities

Zahradnı́k

Janský

Papatsimpa

2001

Pure appl. geophys.

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Ð The ASPO method (Amplitude Spectra and POlarities) for the focal-mechanism retrieval from relatively weak events is based on a widely available instrumental setup: A few broadband stations within a denser short-period network. Collectively all stations provide the epicenter location. Complete records are taken from three-component broadband stations, without selecting a particular wave type, or picking amplitudes. It makes the method suitable for automated data processing, and enables studies of the interference crustal phases. Only the amplitude spectra are inverted. This is a robust feature which makes the method insensitive to any timing problems (such as those due to uncertain origin time, or due to technical failures). The ®rst-motion polarities serve as an additional constraint of the amplitude-spectra inversion; only few (clear) polarities are taken from the nearest stations, where they mostly belong to direct P waves. The method seeks ®ve parameters: The focal depth, scalar moment, strike, dip, and rake. Green's function, automatically including possible near-®eld eects and interference (e.g., surface) waves, is calculated by the discrete wavenumber method. ASPO works below the corner frequency, and the time function is not being retrieved. This feature not only minimizes the number of the inverted parameters, but also speeds up the calculation, because the lower the frequency, the faster the discrete wavenumber run. Instead of an exceedingly slow 5-parameter grid search, the inversion is organized in two steps: (i) the depth and moment determination with a coarse grid search of the strike, dip and rake, and (ii) a ®ne grid search of the three source angles. Uncertainty of the best-®tting solution is assessed from the minimum error value and from the scatter of the nodal lines (and/or P and T axes) between min and min + 10%. The method was tested on the clustered M » 3.5 earthquakes recorded by a temporary network of three CMG3-T broadband stations in western Corinth Gulf. A fundamental problem is that the broadband stations suer systematically from event-induced instabilities at horizontal components if earthquakes of the studied magnitudes occur at short distances, 10±30 km. Therefore, the ASPO method could not be applied below 0.1 Hz. As such, the results are sensitive with respect to unknown crustal structure details, and the focal mechanisms remain rather uncertain (minimum error higher than 0.34). Compared to synthetic tests with perturbed data, in which the error is lower than 0.2, it is concluded that the crustal model needs further improvement.

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The determination of source parameters for small earthquakes from a single, very broadband seismic station

Cited by 69 publications

References 10 publications

Surface Wave Path Corrections and Source Inversions in Southern California

Surface Wave Path Corrections and Source Inversions in Southern California

Near-real-time Seismic Moment-tensor Determination in Spain

Focal Mechanisms of Weak Earthquakes from Amplitude Spectra and Polarities

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