ABSTRACT
Advances in GNSS (GPS) technology as well as the rapid growth of GNSS stations have made it possible to detect pre-signals and pre-slips of a large earthquake and this is an exciting development in the field of earthquake predictions. Analyzing the GNSS data, a pre-signal can be detected before the event. Predictions can be made a few days to few months in advance.
One hundred and sixty two earthquakes (>M6) have occurred in Japan in the eight years from January 2000 and December 2007. These earthquakes were analyzed to determine the presence of pre-signals. Surprisingly, the investigation proved that all earthquakes showed some kind of pre-signals, which means that GNSS data could be useful in predicting earthquakes. Results were validated with analysis of GNSS signals from 1,200 GNSS-based Control Stations, installed all over Japan by Geospatial Information Authority (GSI) since 1996.
Although, it was possible to detect some pre-signals before an earthquake, release of such information to the public was prohibited in Japan. However, such predictions are allowed to be published in the public domain only after the Great East Japan Earthquake (M 9.0 in Richter Scale) that occurred on March 11, 2011 killing nearly 18,000 people, mainly by the Tsunami triggered by the earthquake. An entity called Japan Earthquake Science Exploration Agency (JESEA: http://www.jesea. co.jp) was established in January 2013 for analyzing these signals, predicting earthquakes, and publishing them every week. This information is distributed via an e-mail magazine to registered individuals and organizations. In 2013, pre-signals for eight large earthquakes were picked-up and sent to JESEA members. Subsequently Japan experienced these earthquakes leading to an increased interest in this technology.