Observations of S410p and S350p phases at seismograph stations in California

Abstract

[1] We analyze a new set of seismic data from seismograph stations in California. This data set consists of nearly 5000 S receiver functions for 47 seismograph stations. As a rule, the stacked SRFs display a distinct S410p seismic phase (S wave converted to P at the 410 km discontinuity). The wave paths of S410p sample the upper mantle beneath California and the neighboring region of the Pacific. In northernmost California the S410p travel times are close to those of the IASP91 global model. Further south, S410p usually arrives about 2 s earlier than predicted by the IASP91 model. This early arrival can be explained either by an anomalously high Vp/Vs velocity ratio (1.9 in a 125 km thick layer of the upper mantle versus 1.8 in IASP91), by a depression of the 410 km discontinuity of 15 km, or by a combination of both effects with smaller amplitudes. We observe systematically S350p phase which is converted from a negative discontinuity (with a lower S velocity at the lower side) near a depth of 350 km. The observations of S350p are indicative of a low S velocity layer a few tens of kilometers thick atop the 410 km discontinuity beneath southern California and the neighboring oceanic region. Some receiver functions also display S480p phase, which is interpreted as evidence of an intermittent low-velocity layer in the transition zone.

Crustal thickness variation across the northeast Iran continental collision zone from teleseismic converted waves

“…However, existence of crustal and inter-crustal multiples on the PRFs with the possible same delay time relative to P arrival makes it difficult and uncertain to present such interpretations. In fact, S-receiver functions are the proper tool for monitoring the deep-velocity contrasts available in the upper mantle (e.g., see Vinnik et al 2010).…”

Deep Earth Structure - Transition Zone and Mantle Discontinuities

“…Bagley and Revenaugh (2008) and Bagley et al (2009) studied the transition zone in the Pacific region using ScS reverberations and saw no low-velocity zone atop the 410, except at the Japan slab (50-75 km thick). Vinnik et al (2009Vinnik et al ( , 2010 identified in P and S receiver functions a lowvelocity zone above the 410 in South Africa and in California. Schaeffer and Bostock (2010) found in P and S receiver functions below northern Canada a low-velocity zone at about 340 km depth.…”

Mantle anomalies beneath southern Africa: evidence from seismicSandPreceiver functions

“…The delay is usually in a range from 1 to 2 s, generally close to those at stations BOSA and LBTB. The residuals of traveltime of S410p are almost independent of the mantle S velocity, but sensitive to the V P /V S ratio and the depth of the 410-km discontinuity (Vinnik et al 2009). The positive delays are explained by a low V P /V S ratio or/and an uplifted 410-km discontinuity.…”

“…The detected signal is always seen at the traces corresponding to several values of differential slowness, and its arrival time can be different in different traces. The dependence of the arrival time on differential slowness means that the average signal amplitude differs between the negative and positive differential distances (Vinnik et al 2009). We select the reference distance (the distance at which the moveout corrections change their sign) by trial and error and require that the dependence of arrival time of S410p (Sp converted phase from the 410-km discontinuity) on the differential slowness is minimal.…”