Re-examination of GNSS Data Before the 2004 Chuetsu and the 2007 Chuetsu-oki Earthquakes

Abstract

We analyze GNSS data from GEONET data in the vicinity of the 2004 M6.6 Chuetsu and the 2007 M6.6 Chuetsu-oki earthquakes to assess the existence of crustal deformation anomalies before the events as reported by previous studies. Baseline estimation from different analysis strategies did not reveal systematic differences between the solutions. However, clear deformation patterns were not found from this analysis. On the other hand, evaluation of horizontal displacement rate distributions prior to the occurrence of each event, shows localized patterns: localized contraction is observed in the source region of the 2004 Chuetsu and the 2007 Chuetsu-oki earthquakes after the first event. Additionally, observations to the west suggest that the nucleation of the 2007 Chuetsu earthquake might have started before the 2004 event. Aseismic fault slip might play an important role of the deformation of this region.