Improved Regional and TeleseismicP‐Wave Travel‐Time Prediction and Event Location Using a Global 3D Velocity Model

Abstract

A global validation dataset of 116 seismic events and 20,977 associated Pn and P arrivals is used to assess travel-time prediction and event location accuracy for the global-scale, 3D, P-wave velocity model called LLNL-G3Dv3 (Simmons et al., 2012). Strong regional trends that are observed for ak135 travel-time residuals are largely removed when LLNL-G3Dv3 is used for prediction. The 25th-75th quantile spread of travel-time residuals is reduced by 30%-40% at teleseismic distances, and the spread is reduced by ∼60% at regional distances (< 16°). Epicenter error decreases when more data are used to constrain event locations until more than ∼40 arrivals times are used. At which point, epicenter error reduction tends to plateau. Median epicenter errors for the ak135 and LLNL-G3Dv3 models plateau at ∼8:0 and ∼5:5 km, respectively, for teleseismic P datasets. Median epicenter errors for the ak135 and LLNL-G3Dv3 models plateau at ∼12:0 and ∼4:0 km, respectively, for regional Pn datasets. We demonstrate that spatially correlated travel-time residual errors for the ak135 model lead to increasing epicenter error when ∼40 to ∼100 Pn arrivals are used to constrain the location. The effect of correlated error is mitigated by LLNL-G3Dv3, for which epicenter error steadily decreases to ∼4 km when 100 Pn arrivals are used. The median area of 0.95 epicenter probability bounds for ak135 and LLNL-G3Dv3 are 1811 and 758 km 2 , respectively. The ak135 ellipses are inflated to achieve the desired rate of true events occurring inside the probability region, whereas LLNLG3Dv3 error ellipses based on empirical residual distributions cover the true location at the expected rate because location bias is minimal.

Upper Crustal Weak Zone in Central Tibet: An Implication From Three‐Dimensional Seismic Velocity and Attenuation Tomography Results

“…The azimuthal gaps of shots 2–12 range from 150° to 220°, whereas shot 1 has a larger azimuthal gap of 320°. Myers et al () showed that epicenter errors increase nearly linearly with azimuthal gap between 0° and 220°, and nonlinearly when the azimuthal gap is larger than 220°. The local earthquakes were recorded by 2‐D seismic arrays and have better azimuthal coverage than the shots.…”

Assessing waveform predictions of recent three‐dimensional velocity models of the Tibetan Plateau

“…The starting model in the inversion for G3Dv3 included information in RSTT. A recent study investigated the accuracy of G3Dv3 by applying a 3‐D ray tracing to the prediction of P wave arrival time [ Myers et al , ]. This model consists of 57 layers from the surface to the core‐mantle boundary.…”

Revision of earthquake hypocentre locations in global bulletin data sets using source-specific station terms

“…One approach is to use tomographic velocity models to predict the travel times of seismic phases more accurately. Several studies have demonstrated improved travel-time prediction accuracy using a global 3-D model (Smith & Ekström 1996;Antolik et al 2001;Chen & Willemann 2001;Myers et al 2015). However, although the obtained velocity information provides enhanced absolute hypocentre locations by reducing the biasing effects of large-scale velocity structure, usually only a smooth model can be obtained, which cannot effectively account for small-scale velocity heterogeneities, particularly when applied to global earthquake location.…”