A dense GPS observation immediately after the 2004 mid-Niigata prefecture earthquake

Abstract

To investigate the postseismic crustal deformation associated with the 2004 mid-Niigata prefecture earthquake (M6.8), we newly started GPS observation to fill a gap of the nationwide continuous GPS network. Our GPS sites were mainly distributed in the focal region without permanent GPS site, and succeeded in obtaining the postseismic deformation. Coseismic displacements of two aftershocks were clearly detected because of immediate observation. Estimated fault parameters of the aftershock (M5.9) on November 8 occurring just beneath our GPS network indicated that geodetic data could be explained by either east-or west-dipping fault model inferred from detailed aftershock data. Moreover, clear postseismic deformation, which could be characterized by a logarithmic decay function, was observed. This signal probably suggests possible aseismic slip. Our results indicated that dense GPS observation could give important and interesting data to clarify the properties of shallow inland middle-size earthquakes.

Coseismic and postseismic deformation related to the 2007 Chuetsu-oki, Niigata Earthquake

“…The estimated decay time constants range from 0.35 to 2.83 days, with the exception of that for the eastward component at 940051. This decay time constant range is almost similar to that estimated for the 2004 Mid-Niigata Prefecture Earthquake (M j 6.8) by Takahashi et al (2005). The 2004 earthquake was an inland shallow earthquake that occurred about 35 km southeast of the 2007 earthquake; if the mechanism and geometry of the afterslip are similar in both earthquakes, the decay time also should be similar.…”

“…to the observed time series, where t is the elapsed time after the mainshock, τ is the decay time constant, and a is the amplitude of the very common logarithmic law for postseismic deformation study (e.g., Takahashi et al, 2005;Nakao et al, 2006). We estimated a and τ by a non-linear least-squares method.…”

Postseismic deformation following the 2016 Kumamoto earthquake detected by ALOS-2/PALSAR-2

“…What about thrust events? Takahashi et al (2005) observed postseismic displacement of 3 cm or larger during about 2 months after the 2004 Niigata Chuetsu earthquake (M JMA 6.8, M w 6.6). For the 2007 Noto Peninsula earthquake of M JMA 6.9 (M w 6.7), only 2 cm displacements were observed by campaign GPS surveys by Hashimoto et al (2008).…”

Geodetic evidence of viscoelastic relaxation after the 2008 Iwate-Miyagi Nairiku earthquake

“…Three possible mechanisms, namely afterslip, viscoelastic relaxation and poroelastic rebound (e.g., Feigl and Thatcher, 2006) may account for the postseismic deformation. Although the postseismic deformations of recent Japanese inland earthquakes observed based on GPS measurements have already been discussed (e.g., Takahashi et al, 2005;Iinuma et al, 2008;Ohta et al, 2008b), they assumed only afterslip rather than viscoelastic relaxation or poroelastic rebound. There may be two reasons why they did not consider viscoelastic relaxation: either the effect was too weak to examine or the observation period (a few months) was too short to detect the viscoelastic relaxation, which has a relatively long decay time (several years to decades).…”