| In recent years, GPS has been widely used to survey short period ground deformation with the appearance of high-rate GPS, and it has become an auxiliary tool of seismic instruments. Compared to seismic instruments, high-rate GPS has its own characteristics and advantages in seismology:dynamic deformation displacement can be directly obtained; The greater the surface deformation displacement, the higher the measurement accuracy; There is no amplitude saturation phenomenon, especially when strong earthquake occurs, high-rate GPS can accurately record surface deformation characteristics.At present, most countries have set up their own high-rate GPS continuous observation network, it is mainly used for surface deformation monitoring. And high-rate GPS single epoch dynamic position approaches and processing software have matured and can reach the precision of millimeter in earthquake measurement, the displacement time-series from high-rate GPS are consistent well with seismic instruments, completely can be used as useful as seismic instruments for earthquake studies.Due to the conditions of seismic network, surface wave magnitude is still adopted as a main measure of earthquake strength by our country. After an earthquake, the rapid report system based on seismic network can calculate the epicenter location and surface wave magnitude in a few minutes, but when a very strong earthquake occurs, strong motion often underestimate the surface wave magnitude that is caused by amplitude saturation. In this case, if the high-rate GPS can provide information for the rapid surface wave magnitude inversion, then earthquake magnitude are expected to accurate assessment in strong earthquake quick report and early warning, so we will be able to further reduce the loss caused by the disaster.Given the huge capacity and development status of high-rate GPS, firstly 10Hz GPS data of Lushan earthquake are resolved by R.TKLIB to get the ground moving characteristics, extract the peak horizontal displacement of 20 observations, research the relationship between peak horizontal displacement and epicentral distance, estimate magnitude by the empirical equation that Gutenberg deduced in 1945, explore the high-rate GPS abilities of surface wave magnitude rapid estimates in Sichuan terrain conditions. Then,1 Hz GPS data of El Mayor-Cucapah Earthquake are used to analyze ground motion characteristics, estimate surface wave magnitude by empirical equation that Gutenberg deduced in 1945 and research high-rate GPS observations application scope in surface wave magnitude estimates.The results are as follows:1. For the Lushan earthquake, all sites had different levels of ground moving with centimeter-level, the attenuation relationship between peak horizontal displacement and epicentral distance of GPS observations is approximately exponential scale. Magnitude estimates by the empirical equation that Gutenberg deduced in 1945 of Lushan earthquake is 6.78, and the shortest time to get the robust magnitude is 142s. The results show that high-rate GPS can be applied for the fast estimation of surface wave magnitude in the Sichuan terrain conditions, so fast early warning and emergency response are feasible.2. High-rate GPS that is used for surface wave magnitude estimates by the empirical equation that Gutenberg deduced in 1945 should be considered observations distance to the epicenter. For the 2010 El Mayor-Cucapah 7.2 earthquake, when the stations to the epicenter distance are in 50-350km range, high-rate GPS can provide reliable surface wave magnitude, when using the sites of epicentral distance greater than 350km, the surface wave magnitude are within 7.6 to 8.0. So we suggest when establishing an empirical model of estimating surface wave magnitude with high-rate GPS, its application scope should be considered. |
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