P‐SV conversions of teleseismic waves beneath the Chyulu Hills Volcanic Field, Kenya

Abstract

Observations of P‐SV converted waves provide new insights on the structure of the lithosphere beneath the Chyulu Hills, a Quaternary volcanic field on the SE shoulder of the Kenya rift (East Africa). A 3D teleseismic delay‐time tomography and a seismic refraction model revealed a zone of reduced P‐wave velocity (−3.5%) extending from the lower crust into the uppermost mantle (limited to about 70 km depth). In this paper, waveform and particle‐motion analyses are used to identify P‐SV conversions in teleseismic recordings and to search for lateral variations of seismic discontinuities. Data from 9 teleseisms contain clear SV‐phases within the first 8 seconds of the P‐coda. The depth of the generating interfaces is determined with a local velocity‐depth function based on the seismic refraction model. Our results show that there are no lateral depth variations of the Conrad (19–21 km) and Moho (43–45 km) discontinuities, indicating no large‐scale modification of the crustal structure through the magmatic processes. In the time window between the SV‐arrivals from the Conrad and Moho discontinuities additional SV‐energy is observed at some stations, but its origin cannot be located.