The Beginning To The Compression Wave Direct Imaging Of Earthquake Rupture

The crust rupture process induced by a big earthquake is a complex process. It has been put forward here that an earthquake is the result from the sudden release of stored energy in the Earth's crust,and the rupture in the crust occur as slip along a fault. We can afford the information of the earthquake rupture process by monitoring of seismic waves which reflect the characteristic of rupture duration, direction and intensity. Nowadays broadband, high dynamic range and digital seismic instruments are deployed all over the world, providing us a high level of seismic data both on quantity and quality. And the computer, theory and inverse method of seismic source develop rapidly; we have a strong faith that all these factors accelerate the study on the earthquake rupture process.We employed a back-projection method to image the progression of the transient rupture front by only using of first arriving compressional waves. Our method requires no input on fault geometry which is usually estimated from aftershock distribution. Thus it provides a rapid determination of duration, direction and rupture length of large earthquakes. These observations are key parameters for rapid assessment of immediate seismic hazard.Here we applied a direct imaging technique to the P waves recorded at the China National Digital Seismic Network (CNDSN) and Global Seismic Network (GSN) stations generated by the 2004 great Sumatra-Andaman earthquake and 2001 Kunlunshan earthquake.The 26 December 2004 Sumatra-Andaman earthquake was the largest seismic event on Earth in more than 40 years, and it produced the most devastating tsunami in recorded history that caused more than 300,000 deaths which overage the total death of historical earthquake. So it is urgent to determine the rupture process. Here we present detailed images of the rupture process using the first-arriving compressional waves recorded by the China National Digital Seismic Network (CNDSN). An improved imaging condition was employed to account for the sparse distribution of the CNDSN stations. The resulting images are consistent with the major rupture features reported by previous seismic and geodetic studies. We found that the earthquake rupture initiated at offshore of northwestern Sumatra and propagated in the north northwest direction at a speed of 2.7±0.2 kilometers per second. The rupture continued for at least 420 s and extended about 1200~1300 km along the Andaman trough with two bursts of seismic energy. These conclusions exhibited our CNDSN importance in analyzing and warning of earthquake rupture process.As 2004 Sumatra-Andaman earthquake happened undersea, we can only compared seismic recording to geodetic data while lacking of visualized surface rupture. So we have a further study on the rupture process of 2001 Kunlunshan earthquake which created spectacular and complete surface rupture. By combined the seismic to geodetic and radar recordings, we discussed the details about the earthquake rupture, coseismic and postseismic deformations.Regarding to Kunlunshan earthquake, there is a great inconsistency between the results based on Seismic Network of Capital Area, Seismic Network of Capital Area and CNDSN, and GSN. We determined that rupture propagated on the 400 km long fault at supershear velocity. And we believe that the complex of seismic source, waveform triplications associated with the upper mantle discontinuities, and the different coverage of seismic network lead to various seismic ray paths, which have important role in determining the rupture length and velocity. So it is necessary to have a further study on Kunlunshan earthquake rupture process.In conclusion, the global fluctuation which induced by earthquake rupture provide us precious materials to understand the structure of the Earth. Here we demonstrate that it is feasible and effective to use a weighed stacking algorithm for imaging the rupture process. Also it is necessary to improve the method which can afford three-dimensional images of earthquake process by using a back-projection to P-waves.