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/pl00001169

Cited by 12 publications

(7 citation statements)

References 34 publications

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“…Tremendous work has been done to better locate a seismic event in the context of the CTBT. Various strategies include developing new techniques for more accurate travel time measurements, utilizing travel times together with slowness and azimuth information [e.g., Bondár and North , 1999; Bondár et al , 1999; Uhrhammer et al , 2001], implementing better regional velocity models [e.g., Kremenetskaya et al , 2001], and deriving various source‐specific station corrections [e.g., Yang et al , 2001a, 2001b; Ryaboy et al , 2001]. At the same time, rather than focusing on travel times of impulsive body wave phases, Yacoub [1996] reported locations of 16 nuclear explosions that were well determined by using arrival times of the maximum Rayleigh wave energy estimated over a narrow frequency band of 17–23 s, in the same manner as P wave travel times are used.…”

Section: Introductionmentioning

confidence: 99%

Locating and modeling regional earthquakes with two stations

Tan¹,

Zhu²,

Helmberger³

et al. 2006

J. Geophys. Res.

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[1] We developed a new technique CAPloc to retrieve full source parameters of small seismic events from regional seismograms, which include origin time, epicenter location, depth, focal mechanism, and moment magnitude. Despite rather complicated propagation effects at short periods, a simple localized one-dimensional model can well explain signals of periods 3-10 s if we break the three-component records into different segments and allow differential time shifts among them. These differential time shifts, once established from a calibration process or a well-determined tomographic map, can be used together with P wave travel times to refine an event's location. In this study, we tested whether our new method could produce satisfactory results with as few as two stations, so that we can improve source estimates of poorly monitored events with sparse waveform data. We conducted the test on 28 events in the Tibetan Plateau. The focal mechanisms and locations determined from only two stations agree well with those determined from a whole PASSCAL array. In particular, our new method produces better locations than International Seismological Centre, with the average mislocation error reduced from $16 to $5 km. We also tested whether an event's depth and mechanism can be determined separately from its epicenter relocation in a two-step approach. We find that the two-step approach does not always give the correct solution, but the reliability of a solution can be evaluated using a reduced chi-square value.

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Section: Introductionmentioning

confidence: 99%

Locating and modeling regional earthquakes with two stations

Tan¹,

Zhu²,

Helmberger³

et al. 2006

J. Geophys. Res.

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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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“…For improvement in location accuracy, one or a combination of several approaches is typically chosen, such as a one-dimensional velocity model is replaced with a more complicated and, presumably, more accurate 3-D model (e.g., Darold et al, 2014;Ryaboy et al, 2001), and/or regional or source-specific empirical corrections are applied to travel times from the one-dimensional model (e.g., Myers & Schultz, 2000;Nicholson et al, 2008;Richards-Dinger & Shearer, 2000). If available, ground-truth sources, such as artificial explosions with known locations or natural events with hypocenters highly constrained by a dense local network, are used to calibrate arrival-time corrections (e.g., Bondár et al, 2001Bondár et al, , 2004Bondár & McLaughlin, 2009).…”

Section: Introductionmentioning

confidence: 99%

Improving Absolute Earthquake Location in West Texas Using Probabilistic, Proxy Ground‐Truth Station Corrections

Lomax¹,

Savvaidis

2019

JGR Solid Earth

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An increase in induced seismicity in the central United States since 2009 led to establishment of TexNet seismic-monitoring in Texas. Accurate, absolute seismic-event location is critical to TexNet, allowing quantitative evaluation of possible association of seismicity with human activity. For the Delaware Basin, western Texas, relocation using different velocity models and TexNet station subsets shows absolute location error up to 4-5 km. The preferred method to reduce absolute error, ground-truth calibration, is not available in this area. Alternatively, we used industrial well activity as proxy, ground-truth for developing probabilistic, proxy ground-truth (PPGT) station corrections for relocation. Assuming well activity causes seismicity, we defined a distance-time probability associating events and well activity. We used these associations and other evidence to show some seismicity in the Delaware Basin is more likely due to hydraulic-fracturing than saltwater disposal. We then probabilistically accumulated PPGT station corrections using event hypocenters constrained to associated fracturing-well locations. We applied this procedure within 12 km of TexNet station PB02, optimizing the procedure through comparison of rates of causal and acausal associations. Relative to the initial locations, final PPGT relocations show smaller residuals and shifts in epicenter as much as 3 km, predominantly toward the north and northwest. PPGT residuals are similar to those from relocation with standard station corrections. The initial hypocenters showed an unreasonable deepening with distance from station PB02, whereas PPGT relocations produced an overall flattening of event depths. These results are consistent with PPGT corrections giving real improvement in absolute location accuracy.Plain Language Summary The TexNet seismic-monitoring program in Texas was established in response to an increase in human-induced earthquakes in the central United States since 2009. Accurate determination of the geographic location and depth in the Earth of earthquakes is critical to TexNet monitoring, allowing potential association of earthquakes with human activity. But accurately locating earthquakes is difficult due to lack of geologic knowledge and sparsity of seismic monitoring stations. For a study area in western Texas, errors in TexNet earthquake location and depth may be as much as 4-5 km. Ideally, accuracy would be improved by calibration of the seismic network using ground-truth seismic events, such as quarry blasts, but such information is unavailable in this area. Instead, assuming that some earthquakes could be caused by hydraulic-fracturing in the study area, we statistically associate earthquakes in space and time to fracturing activity. We then use the known locations of this associated activity as proxy ground-truth to calibrate the seismic network. Our results suggest some earthquakes in west Texas are more likely due to hydraulic-fracturing than saltwater disposal. Quality measures and spatial patterns of earthquakes relo...

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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 12 publications

References 34 publications

Locating and modeling regional earthquakes with two stations

Locating and modeling regional earthquakes with two stations

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

Improving Absolute Earthquake Location in West Texas Using Probabilistic, Proxy Ground‐Truth Station Corrections

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