Quick aftershock relocation of the 1994 Shikotan Earthquake and its fault planes

Self Cite

We relocated the mainshock and immediate aftershocks of the 1964 Niigata earthquake (M s 7.5) using both the modified joint hypocenter determination (MJHD), and the grid search (GS), methods to obtain their hypocenters and identify the fault plane of the mainshock. We used P-wave arrival times at 13 Japanese stations reported by the Japan Meteorological Agency (JMA). Firstly, we performed the MJHD method to select readings with high accuracies and to obtain station corrections that related to the lateral heterogeneity of the Earth's structure. Secondly, we performed the GS method by using only selected readings and assuming the station corrections. Based on the relocated hypocenters, we found that the mainshock and immediate aftershocks occurred along a plane striking N15• E and dipping 11• eastward. This result strongly suggests that one of the nodal planes of the mainshock, for which the strike and dip are N9• E and 34• , respectively, is preferable as the fault plane. When global stations are also used for relocations, the results confirm that the fault plane of the 1964 Niigata earthquake dips gently eastward. Therefore, we concluded that the fault plane of the 1964 Niigata earthquake is gently eastward-dipping.

Section: Results Of the Grid Search Methodsmentioning

confidence: 99%

Section: Methods and Datamentioning

confidence: 99%

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Fault plane of the 1964 Niigata earthquake, Japan, derived from relocation of the mainshock and aftershocks by using the modified joint hypocenter determination and grid search methods

Hurukawa

Harada

2013

Self Cite

“…For this reason, Imoto (1990, 1992) developed the MJHD method for locating local earthquakes, in which station correction is independent of both the distance and azimuth from the center of the studied region to the given station, thereby improving the stability of the method. Subsequently, Hurukawa (1995) extended the MJHD method for locating teleseismic earthquakes; we use this extended version in this study, and we used the iasp91 model for the estimation of travel times. …”

Section: Methodsmentioning

confidence: 99%

Relocation of the 2011 off the Pacific coast of Tohoku earthquake sequence and fault planes of M ≥ 7 earthquakes

Hurukawa

2011

Self Cite

We relocated foreshocks, mainshock, and aftershocks of the 2011 off the Pacific coast of Tohoku Earthquake (M w 9.1) using the modified joint hypocenter determination (MJHD) method in order to obtain their precise hypocenters and to identify fault planes of larger earthquakes. We used P-wave arrival times at stations worldwide reported by the U.S. Geological Survey (USGS). We confirmed by relocated hypocenters that the mainshock and aftershocks had occurred along the plate boundary between the North American and Pacific plates. We also confirmed that the M w 7.5 foreshock, which occurred two days before the mainshock, and the largest aftershock (M w 7.9), which occurred half an hour after the mainshock, were thrust earthquakes along the plate boundary. The second largest aftershock (M w 7.6), which was a normal-faulting earthquake and was a bending-stress intraplate event caused by the strain reduction on the subduction thrust, occurred at the outer rise of the Japan Trench and was well relocated with its aftershocks. We found that its fault plane dipped westward and it bounded the aftershock distribution on the seaward side. This implies that the western side of the fault plane had subsided, corresponding with the westward plate subduction.

“…However, we think that the relocated hypocenter locations might have been affected by local velocity structure heterogeneity and by the poor network distribution which was located on one side of the aftershock area. In order to overcome this difÀculty, we conduct a simultaneous relocation of the 1994 and 2000 main shocks and aftershocks using Hurukawa's (1995) ModiÀed Joint Hypocenter Determination (MJHD) method.…”

Section: Introductionmentioning

confidence: 99%

Two parallel trench-normal fault planes within the Pacific slab associated with the 1994 and 2000 Kurile earthquakes as revealed by simultaneous relocation of their main shocks and aftershocks

Harada

Ishibashi

2007

The 1994 Hokkaido-Toho-Oki (M w 8.3) and the 2000 Nemuro-Hanto-Oki (M w 6.8) earthquakes have been regarded as great/large intraslab events within the subducted PaciÀc plate along the southern Kurile trench. Determining which nodal planes of their mechanism solutions are actual fault planes and whether or not the 2000 event occurred on the southwestern extension of the 1994 fault plane have been problematic. In order to clarify these points, we examine the relative location of their main-shock and aftershock distributions accurately by simultaneous relocation of their hypocenters using the ModiÀed Joint Hypocenter Determination (MJHD) method. The result clearly shows that the two earthquakes occurred on trench-normal shallow-dipping fault planes within the PaciÀc slab, apart from and parallel to each other. Therefore, the 2000 earthquake was not a rupture on the deeper extension of the 1994 fault plane, but one on another fault plane. A large intraslab earthquake (M w 7.8; depth, about 100 km) occurred to the northwest of the 1994 event in 1978, and two trenchnormal fracture zones exist outside the trench to the southeast of the 1994 and 2000 events. Therefore, these three intraslab great/large earthquakes are considered to have been ruptures along pre-existing trench-normal weak zones within the subducted PaciÀc plate.