The same phase to two different arrivals. Is assigned in a probabilistic manner based on the relevant PDF values, making sure not to assign When PDFs overlap for a particular depth phase, phase identification Probability density functions (PDF) for depth phases,Ĭentered on their theoretical relative travel times for a given hypocenter, are compared to the Using a probabilistic association algorithm. Hence, depth phase arrivals are re-identified after each iteration in the EHB procedure However, a problem with the use ofĭepth phases is that their correct identification often requires knowledge of the event depth andĭistance. Their travel time derivatives are opposite in sign to direct P. Depth to origin time trade-off is avoided by the inclusion of depth phases (pP, pwP, sP) because Phases because their travel-time derivatives differ significantly in magnitude from those of direct Additional constraints are often provided by these S- and P-wave core phases at critical azimuths. For events having a poorĪzimuthal distribution of P-wave arrivals, epicenter constraints are improved by the inclusion of Provide greater constraints on hypocenter parameters, especially focal depth. Many studies have shown that the inclusion of later arriving phases can Until recently, standard teleseismic catalogs (ISC, NEIC) relied almost entirely on first arriving P Symmetric, P- and S-velocity Earth model that provides a good average fit to reported phase arrival times.Ī direct method to improve seismic event locations is by better utilization of the data. Thus, for global earthquake location there has been convergence on a global, radially Most core phase times are quite well matched and aīaseline problem with Jeffreys-Bullen (JB Jeffreys and Bullen, 1940) travel times for PKP phases (Kennett and Engdahl, 1991) has been removed. The mantle S wave bias of the earlier iasp91 (1998) have shown that the model ak135 (Kennett et al., 1995) provides a very goodįit to a wide range of seismic phases. The selection of magnitudes for events prior to 1964 is described in Engdahl and Villasenor (2002).Įngdahl et al. Taken from the ISC bulletin, and the provenance of Mw values is the global CMT catalogue. The EHB algorithm does not recalculate magnitudes the vast majority of the mb and Ms values are
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