Regional Seismic Traveltime Tomography Of Java Island

At present,seismic tomography method has been used to study the heterogeneous structure of the earth's interior,among which traveltime tomography is a method to invert the velocity model of underground media by using the traveltime of seismic waves and the ray path of their propagation.It is one of the most widely used tomography method.This paper introduces some basic theoretical knowledge of seismic tomography and fast marching method,describes the ray tracing process of fast marching method in detail,introduces the improved fast marching method,derives the relevant formula of three-dimensional fast marching method when irregular nodes exist,and verifies the rationality of the improved method.In this study,the regional seismic data that occurred on Java Island from January 2009 to March 2019 recorded by 52 stations distributed on Java Island were selected The boundary of study area is-3—-12·N,104·—118·E.In order to ensure the accuracy and reliability of the tomography results,the selected magnitudes were all greater than 2.5.The list of earthquakes is first obtained from the International Earthquake Center's event catalog,and then the seismic records of these earthquakes are downloaded from the Seismic Network of the Indonesian Meteorological,Climate and Geophysical Bureau.After preprocessing the waveform by removing the average value and trend,and the seismic instrument resopnds.and then the waveform is band-pass filtered in the frequency range of 0.5-1.5 Hz.The cross-correlation traveltime was obtained by solving the eikonal equation.In this paper,a total of 10229 reliable P-wave relative travel time residual data from 965 regional earthquakes were picked up using an adaptive iterative technique based on the Multi-channel Cross-correlation method.Then the Fast Marching Teleseismic Tomography method was used to obtain the P-wave velocity structure at a depth of 300KM in Java Island.The results showed that the low-velocity bodies mainly existed in the depth range of 40-60KM.The position of the trench and the corresponding plate subduction continuously moved northeastward.