Seismic constraints on subduction of the fossil ridge beneath Luzon Island, Philippines

Abstract:

The subduction of a preexisting facture zone appears to control many aspects of the subducting process, including the stress field, mantle melting and geochemical signature on the overriding plate. The fossil ridge in South China Sea (SCS), along with the overriding seamounts, is now subducting along Manila trench below the Luzon Island, Philippines, providing a unique setting to study such a complex process. Here we present an upper mantle P-wave velocity structure derived from a finite frequency teleseismic tomography using primarily OBS data in SCS. The OBS data was collected from two passive source experiments carried out along the fossil ridge close to Manila trench. Both the deployments were over six months, and they retrieved valid data at 10 and 6 OBSs, respectively. To constrain the upper mantle structure beneath Luzon, we will employ the Source Side Seismic tomography (3STomo) method, in which the roles of station and earthquake are interchanged compared to the conventional teleseismic tomography. We will combine the 3STomo with the conventional tomography using OBSs and a few land stations to construct an upper mantle structure model for the whole region. We expect our seismic images would be helpful to explain the seismicity pattern and the geochemical signature observed on Luzon Island.