|dc.description.abstract||Inversion of the earthquake source information by using seismic data becomes effective and performs well in the last decades. Such information, including source location, earthquake magnitude and focal mechanism, are important for earthquake and tsunami early warning studies.
When earthquakes occur, a preliminarily calculation for earthquake magnitude is based on the amplitude of short period seismic waves in the near-field. However, for larger earthquakes, the energy need more time to release, which constrain the amplitude of high-frequency energy to a constant. Such a phenomenon is called magnitude saturation, which leads us underestimating the true magnitude of large and also devastating earthquakes. In order to calculate the magnitude closer to the real magnitude, immediately after an earthquake, the near-field and low-frequency information from the source are important and necessary.
Global Positioning System (GPS) takes advantage on the resolving power of low-frequency rupture behavior and overcomes the records clipping in the near-field, which is an ideal instrument for large earthquake. In order to calculate the focal mechanism, source location, and magnitude in a few seconds following an earthquake, this research builds a GPS-based focal mechanism inversion method for Taiwan. To test whether the model works properly, I test three local magnitudes ML >6 earthquakes occurred in 2013, Taiwan. Two earthquakes are of ML 6.2 and 6.5 occurred in Nantou County, in the central Taiwan with close epicentral locations within a distance about 8.5 km, namely the 0327 and 0602 earthquakes, respectively. Another earthquake occurred near Ruisui town, in the eastern Taiwan with ML 6.4, called the Ruisui earthquake. I also test two additional events for a larger occurred in 2002 of ML 6.8, called 331 earthquake; and the other occurred in 2003 of ML 6.4, called Chengkung earthquake. All the results showed good agreements with the results from GCMT and BATS, which evaluate the source parameters from dynamic wave information. Such success shows that GPS measurements alone can provide important information for inverting earthquake source model parameters.