A study of Pn anisotropy beneath continent in East Asia

Abstract

Seismic anisotropy is of importance in elucidating the dynamic process in the past and the present of the Earth's interior. If a faster propagation of seismic waves in any azimuth is confirmed, the direction of anisotropy can be estimated beneath the continent. We use Pn waves propagating along the mantle lid to constrain seismic anisotropy in the uppermost part of the upper mantle. We collected Pn arrival times of all events ranging from 1.5° to 15° in epicentral distance in and around East Asia from 1960 to 2011 from the Bulletin of the International Seismological Centre. Pn velocity was estimated using a two-station method to eliminate any unwanted effect of timing error such as misreading of arrival times from analog seismograms recorded in the early instrumental age. Anisotropic regions vary with Pn velocity depending on the azimuth. We create a grid of 1° intervals throughout East Asia. Then seismic anisotropy is identified by the distribution of Pn velocities estimated within a circular spatial window moving on the grid. We then obtain estimates of velocity from each radius caps. The inversion is performed using data of estimates. There are two type of periods which is cos(2φ) and cos(4φ) from the inversion. Results may appear important points related with plate process.