Searching for Silent Earthquakes with Geodetic Data

Takeshi SAGIYA


The Japanese nationwide GPS array has dramatically improved the detectability of silent earthquakes. A method for reducing regular displacement components of GPS daily coordinate data is presented. GPS data has shown anomalous slow deformations from the Boso Peninsula, western Tokai area, and so on. The results of 7 years of observation may not give us complete knowledge about the silent eartuquakes because of the short observation time. Conventional geodetic data provide supplementary information for the discussion of silent earthquakes in a longer term. The results of geodetic data analysis indicate that we will be able to accumulate more and more examples in the future.


1. Introduction
2. Search with GPS data
  2.1 Searching strategy
  2.2 Selection of reference sites
  2.3 Silent earthquakes around Choshi
  2.4 1996 Boso Peninsula silent earthquake
  2.5 2001 Tokai slow earthquake
  2.6 Other slow events
3. Search with conventional survey data
  3.1 Importance of conventional survey data
  3.2 Recurrence of silent thrust events in the Tokai area
  3.3 Anomalous vertical deformation in the southern Kanto district
4. Discussion
5. Conclusion