Preliminary Study Of Real-time Evolutionary Location Method In 3D Complicated Medium

Earthquake Early Warning (EEW) refers to a practice in which seismic data are collected and analyzed quickly after a significant seismic event, so that the results can be effectively used for postearthquake emergency response and early warning by raising alarm before arrival of the destructive S wave.Routine location algorithms usually start after 4 or 5 triggers, it will not satisfy the EEW demands where the station coverage is not dense enough. In order to locate earthquakes earlier, we try to introduce 3D crust model to construct travel time table with 3D space grids distribution, and design probability density function with arrival times of the triggered stations and the position information of not-triggered stations to locate earthquakes quickly using the Oct-tree searching method based on the "trigger-non-trigger" location method. The major contents of this paper are listed as follows.1 Firstly, we review several methods of earthquake location, rapid report and earthquake early warning systematically, and give a brief account of real-time seismology systems in different countries. The location result from the 3D real-time location method used in this paper not only fast enough for EEW. but also as accurate as routine location methods.2 We take Crust2.0 for example to construct 3D crust model of ShanGanNing area. QingHai area. ShanXi area. SiChuan area. Capital Circle area. West of XinJiang area and YunNan area and compute the 3D space traveltime grids using seismic wavefront-tracing program in software FMTOMO. The grid scale is about 5km×5km×5km. Model computer can sample 20000 times in target area in 1 second (Intel.2.83GHz CPU Clock Speed.16G Memory). This lays the foundation for 3D real-time location.3 We collect and process the wave data of five events from China earthquake network catalog and locate them off-line with a 3D real-time location software. In this paper, we give the location error of each trigger of 3 or 4 triggers and the final variance of arrival time. The location result is compared with the result using IASPE191 model and the result adding disturbance to arrival-time picking. At last we evaluate the location time and radius of EEW dead zone after 2 and 3 triggers. It is shows that the 3D real-time location method can restrict epicenter and depth of source well after 3 triggers:the location result is accurate enough even at the edge of the meshing area:it is more exactly that using 3D crust model (Crust2.0) than horizontal layered model (IASPEI). but because of the minuteness of the change of the vertical wave velocity, there are not much improvement of the accuracy:the arrival-time picking error effect is small.4 We evaluate the capability of the EEW in China mainland simply in case of the completion of the "Rapid Reporting of Seismic Intensity and Earthquake Early Warning Projection". Single-trigger location in EEW intensive monitoring areas where the average distance between stations is less than 40km will make an epicenter voronoi cell radium less than 20km. If we locate earthquakes after 3 triggers, the location time in most areas in China mainland will be in 15 seconds. This will achieve the goal of the projection that sending EEW information in 5-30s after an event (M>5.0) detected at EEW intensive monitoring areas, and M>6.0 at other areas.3D earth structure model have gained after tomography using body wave or surface wave and reflected wave prospect section, so that with the development of computer, location with these models has become a realizable goal. The research in this paper shows that at a proper network density, this 3D real-time location method can give epicenter position in seconds after an earthquake happen, and this is enough for EEW.