Application of 3-D Crustal and Upper Mantle Velocity Model of North America for Location of Regional Seismic Events

Ryaboy, Vladislav; Baumgardt, Douglas R.; Firbas, Petr; Dainty, Anton M.

doi:10.1007/978-3-0348-8250-7_7

Cited by 3 publications

(3 citation statements)

References 20 publications

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“…A major research effort is currently underway (e.g. Firbas 2000; Group‐2 Calibration Consortium 2000; Ryaboy et al 2001) to calibrate the IMS seismic network with station corrections derived from regional and global 3‐D velocity models.…”

Section: Introductionmentioning

confidence: 99%

J362D28: a new joint model of compressional and shear velocity in the Earth's mantle

Antolik

Ekström

et al. 2003

Geophysical Journal International

104

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SUMMARY The discrimination between chemical and thermal heterogeneity in the Earth's mantle remains one of the most important and challenging questions to be answered by observational and theoretical geophysics. To answer this question requires a thorough knowledge of the ratio between compressional and shear velocity anomalies. We describe results of a joint inversion for compressional and shear velocity in the mantle using a large and diverse data set consisting of traveltimes, complete waveforms and surface wave dispersion measurements. A horizontal tessellation consisting of 362 spherical splines is used to parametrize the model, which is approximately equivalent to a spherical harmonic of degree 18 in resolution. The model contains peak variations (from PREM) of up to ±7 per cent in S velocity and ±2.5 per cent in P velocity in the upper mantle. These variations decrease to ±1.5 and ±0.6 per cent, respectively, at 1000 km depth and reach ±2.5 and ±1.0 per cent, respectively, in the D″ region. The rms ratio of S to P velocity perturbations is fairly constant between 2.0 and 2.5 in the lower mantle, but a local minimum in this ratio occurs at a depth of approximately 1700 km. Resolution tests show that the recovery of P and S velocity is not geographically uniform, but also show that this amplitude ratio is well resolved between 670 and 2700 km depth. We also observe a persistent negative correlation between bulk‐sound and shear velocity throughout the same region of the mantle. In addition, the model contains a minimum correlation between P and S velocity between 670 and ∼1100 km. This feature is supported by both the favourable outcome of resolution experiments and the poor fit provided by the starting model from the inversion (in which the P and S velocities are perfectly correlated) to our data set of P‐wave traveltimes. The power spectra of both P and S velocity heterogeneity are similar, although we note a slightly larger dominance of degree two in the spectra for P velocity in the mid‐mantle where resolution is highest.

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Section: Introductionmentioning

confidence: 99%

J362D28: a new joint model of compressional and shear velocity in the Earth's mantle

Antolik

Ekström

et al. 2003

Geophysical Journal International

104

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“…Recent studies have demonstrated that regional path calibration is essential for obtaining accurate locations of seismic events at all magnitudes (RUSSIAN FEDER-ATION/UNITED STATES CALIBRATION WORKING GROUP, 1998;SAIKIA et al, 1996a, b;THIO et al, 1999;ZHU et al, 1997;RYABOY, 1999). Accurate locations are integral to Comprehensive Test-Ban Treaty (CTBT) seismic monitoring eorts, particularly for smaller events, and are also crucial to many types of calibration studies.…”

Section: Introductionmentioning

confidence: 99%

“…Accurate locations are integral to Comprehensive Test-Ban Treaty (CTBT) seismic monitoring eorts, particularly for smaller events, and are also crucial to many types of calibration studies. RYABOY (1999) has demonstrated that applying corrections for regionalized velocity models to the travel times of regional phases from nuclear explosions reduces location errors signi®cantly, putting the relocations on par with announced event locations. Smaller (M < 5) events may only be recorded by a few stations, often with poor azimuthal coverage; consequently their hypocenter error ellipses can be extremely large, especially when located by only a few teleseismic observations (BONDA Â R, 1998).…”

Section: Introductionmentioning

confidence: 99%

Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling

Saikia¹,

Woods²,

Thio³

2001

Pure appl. geophys.

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Ð Regional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller (M < 4.8) seismic events. This path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration (or master) events. This information can be dicult to obtain, especially for smaller events. Generally, explosion or quarry blast generated travel-time data with known locations and origin times are useful for developing the path calibration parameters, but in many regions such data sets are scanty or do not exist. We present a method which is useful for regional path calibration independent of such data, i.e. with earthquakes, which is applicable for events down to M w 4 and which has successfully been applied in India, central Asia, western Mediterranean, North Africa, Tibet and the former Soviet Union. These studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events. We ®nd that the error in source depth does not necessarily trade-o only with the origin time for events with poor azimuthal coverage, but with the horizontal location as well, thus resulting in poor epicentral locations. For example, hypocenters for some events in central Asia were found to move from their ®xed-depth locations by about 20 km. Such errors in location and depth will propagate into path calibration parameters, particularly with respect to travel times. The modeling of teleseismic depth phases (pP, sP) yields accurate depths for earthquakes down to magnitude M w 4.7. This M w threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth, with the relative amplitude of the P nl waves to the surface waves and the interaction of regional sPmP and pPmP phases being good indicators of event depths. We also found that for deep events a seismic phase which follows an S-wave path to the surface and becomes critical, developing a head wave by S to P conversion is also indicative of depth. The detailed characteristic of this phase is controlled by the crustal waveguide. The key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms. The regionalization scheme can also incorporate mixed-path crustal waveguide models for cases in which seismic waves traverse two or more distinctly dierent crustal structures. We also demonstrate that once depths are established, we need only two-stations travel-time data to obtain reliable epicentral locations using a new adaptive grid-search technique which yields locations similar to those determined using travel-time data from local seismic networks with better azimuthal coverage.

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Enhanced hypocenter determination of the 2017 Pohang earthquake sequence, South Korea, using a 3-D velocity model

Jung¹,

Woo²,

Rhie³

2022

Geosci J

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Application of 3-D Crustal and Upper Mantle Velocity Model of North America for Location of Regional Seismic Events

Cited by 3 publications

References 20 publications

J362D28: a new joint model of compressional and shear velocity in the Earth's mantle

J362D28: a new joint model of compressional and shear velocity in the Earth's mantle

Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling

Enhanced hypocenter determination of the 2017 Pohang earthquake sequence, South Korea, using a 3-D velocity model

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