Source Processes of 15 September 1998 M 5.0 Sendai, Northeastern Japan, Earthquake and Its M 3.8 Foreshock by Waveform Inversion

Okada, Tomomi; Umino, Norihito; Ito, Yoshihiro; Matsuzawa, Toru; Hasegawa, Akira; Kamiyama, Makoto

doi:10.1785/0120000240

Cited by 22 publications

(12 citation statements)

References 28 publications

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“…Aftershocks were distributed on the fault plane in a 3×3-km region as shown in Fig. 1(d) and (e), and these were comparable with the spatial extent of the M=5.0 event rupture area estimated by waveform inversions (Okada et al, 2001). Umino et al (2002a) suggested that this earthquake slipped at the deepest portion of the NRF, based on the geometrical relationship between the fault plane of the M=5.0 event and the surface trace of the NRF.…”

Section: Seismotectonic Settingsupporting

confidence: 76%

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

et al. 2006

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An M=5 earthquake occurred on September 15, 1998, in the Nagamachi-Rifu fault (NRF), northeastern Japan. In the aftermath of this event, many seismograph stations were constructed temporarily around the fault, forming a dense network of stations with a spatial separation of 5 km. We report here our estimation of the threedimensional velocity structures of the P and S waves using arrival-time data recorded at these stations with the aim of understanding the heterogeneous structure around the NRF. Low-Velocity and high Poisson's ratio anomalies are imaged in the lower crust beneath the volcanic area, which are probably associated with the partially molten materials conveyed through the upwelling flow in the mantle wedge. A distinct low-velocity anomaly, which is explainable by the existence of H 2 O-filled pores, is observed in the mid crust at the deeper extension of the NRF. Two low-velocity anomalies that are probably associated with the remnants of magmatic activity that formed the Shirasawa caldera and with the existence of thick late-Cenozoic sedimentary layers are observed at depths shallower than 10 km in the hanging wall of the NRF. Our results successfully characterize the major features of the complex velocity structure around the NRF, with implications for the existence of fluid-rich regions in the mid to lower crust.

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Section: Seismotectonic Settingsupporting

confidence: 76%

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

et al. 2006

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“…Mori (1996) studied the source processes of the 1992 Joshua Tree Earthquake (M6.1) and its foreshock (M4.3), which occurred two hours before the mainshock, and concluded that the rupture of the mainshock was initiated near the edge of the ruptured region by the foreshock. Okada et al (2001) studied the source processes of the M5.0 earthquake and its M3.8 foreshock, which occurred near the bottom of the Nagamachi-Rifu fault in 1998. They showed that the rupture area of foreshock does not strongly overlap with the asperities of the mainshock.…”

Section: Discussionmentioning

confidence: 99%

“…However, a waveform inversion with 1-D Green's functions has only limited resolution. We have to introduce empirical Green's functions (e.g., Ide, 1999;Okada et al, 2001) or theoretical 3-D Green's functions . Such a study will be carried out in the future.…”

Section: Discussionmentioning

confidence: 99%

Source processes of the foreshock, mainshock and largest aftershock in the 2003 Miyagi-ken Hokubu, Japan, earthquake sequence

Hikima

Koketsu

2014

Earth Planet Sp

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The waveform inversions for the 2003 Miyagi-ken Hokubu earthquake sequence were performed using strongmotion records to determine the source processes. We carried out the inversions for the foreshock (M5.6), the mainshock (M6.4) and the largest aftershock (M5.5), respectively. The strong-motion waveforms observed at 10 stations from KiK-net and K-NET within about 70 km epicentral distance were used. The mainshock is composed of two subplanes dipping toward west. The strike direction of the south subplane is NE-SW and that of the north subplane is almost N-S. The fault plane of the foreshock is almost the same as that of the south subplane of the mainshock, but the strike direction of the largest aftershock is NW-SE. The asperities of the three earthquakes are not overlapped strongly each other and it is considered that this earthquake sequence is a result of seismic activity on a reverse fault, which is curved along strike, with time lags. The shallow asperity of the mainshock may result in specific distributions of damage and high accelerations.

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“…6), there are some west-dipping reflectors near the hypocenter area of 1998 Mj 5.0 Sendai earthquake. The fault plane determined by the focal mechanisms and hypocentral distribution shows dip to the northwest at an angle of 30 degrees (Umino et al, 1999;Okada et al, 2001). The gently west-dipping reflectors at the depth of 12-13 km on the western half of seismic line A is interpreted as the probable deeper extension of the Nagamachi-Rifu fault (Fig.…”

Section: The Deep Geometry Of the Nagamachi-rifu Faultmentioning

confidence: 97%

Tectonic evolution and deep to shallow geometry of Nagamachi-Rifu Active Fault System, NE Japan

et al. 2014

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The Nagamachi-Rifu fault is an active reverse fault which trends NE-SW across the central part of Sendai City for over 21 km distance. The fault does not emerge at the surface and, accompanied with the Dainenji-yama fault, shows wedge thrusting in the Tertiary sediments. The amount of net slip of the master part of the Nagamachi-Rifu fault is estimated to be one mm/year. Seismic reflection profiles across the fault plus a gravity anomaly reveal the thicker Neogene sediments on the hanging wall rather than on the footwall. The Neogene sedimentary basin was formed by normal faulting in early Miocene under an extensional stress regime associated with the formation of the northern Honshu rift system. Due to shortening deformation since the Pliocene, this Miocene normal fault reactivated as a reverse fault. Judging from the CMP deep seismic reflection profile and location of the 1998 M5.0 Sendai earthquake, the deep geometry of the Nagamachi-Rifu fault is listric.

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Source Processes of 15 September 1998 M 5.0 Sendai, Northeastern Japan, Earthquake and Its M 3.8 Foreshock by Waveform Inversion

Cited by 22 publications

References 28 publications

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography

Source processes of the foreshock, mainshock and largest aftershock in the 2003 Miyagi-ken Hokubu, Japan, earthquake sequence

Tectonic evolution and deep to shallow geometry of Nagamachi-Rifu Active Fault System, NE Japan

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