Journal of the Seismological Society of Japan最新文献

{"title":"Change of Static Stress Fields from Earthquake Rupture in Heterogeneous Crustal Structure","authors":"S. Tone, T. Miyatake, K. Hikima, A. Kato","doi":"10.4294/ZISIN.62.97","DOIUrl":"https://doi.org/10.4294/ZISIN.62.97","url":null,"abstract":"To understand earthquake triggering, computation of Coulomb stress change (ΔCFF) associated with earthquake slip is a powerful tool. However, uniform half space is usually assumed in the computation, though highly heterogeneous crustal structures have been estimated in source regions. The purpose of this study is to evaluate the effect of heterogeneity on the calculation of static stress field. In order to calculate stress field from fault slip in a heterogeneous half space, we solve the equation of motion using 3D finite difference method in which the Lame's constants vary with position. Since fault slip is represented by double couple force system, we apply equivalent body forces in our finite difference grids. First, we calculated stress and ΔCFF field for several simple 2D models to easily understand the effect of heterogeneous medium on ΔCFF field. For two-layered medium, stress is amplified on the region with larger elastic constants. The ratio of the stress amplification is less than the ratio of elastic constants between two layers, which is explained by interaction between two layers. For simplified basin structure and shallow thrust fault below, ΔCFF is larger near the basin and smaller in it than that of uniform structure. We also discuss the effect of heterogeneity near subducting plate on ΔCFF. We found that the subducting plate structure expands the area of positive ΔCFF in the region where outer rise earthquakes occur. Second, we apply the 3D calculation to the 2004 Chuetsu (mid-Niigata prefecture) earthquake (Mw 6.6) and four large aftershocks (MJMA >6). Hikima and Koketsu (2005) and Miyazawa et al. (2005) calculated distribution of ΔCFF for the homogeneous crustal structure and concluded that ΔCFF values just before each aftershock was positive at the hypocenters of the major aftershocks. However, since the structure is complex in the source region, it is important to consider the effect of heterogeneity. We used the fault models estimated by Hikima and Koketsu (2005) and the 3D structure model by Kato et al. (2006) in computation of ΔCFF. The results show that the large aftershocks occurred in the area with positive values of ΔCFF.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126506795","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Source Modeling of the 2007 Niigataken Chuetsu-oki Earthquake Using the Empirical Green's Function Method","authors":"Yosuke Yamamoto, H. Takenaka","doi":"10.4294/ZISIN.62.137","DOIUrl":"https://doi.org/10.4294/ZISIN.62.137","url":null,"abstract":"The 2007 Niigataken Chuetsu-oki earthquake (MJMA6.8) occurred on July 16th, 2007. In this study, we estimate a source model of this earthquake through forward modeling of local strong motion records using the empirical Green's function method. The target frequency range of this modeling is broadband (0.3 Hz to 10 Hz). As the result, the first asperity was estimated that it was located on the NW-dipping fault plane including the hypocenter, and the rupture then transferred to the conjugated fault plane (SE-dipping plane). On the SE-dipping plane, two asperities are identified: one is located just near the first asperity (the second asperity); the other is off the coast of Kashiwazaki city (the third asperity). The estimated three asperities are located in the gaps of the aftershock distribution. Our source model can successfully reproduce strong motion in a wider area than the modeling area selected for source estimation. The estimated stress drop from our source model is almost 15 to 20 MPa, and it is similar to the stress drop empirically expected from the seismic moment and area of asperities.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"264 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123317363","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Source Fault of the Iwate-Miyagi Nairiku Earthquake in 2008 Estimated by Distribution of Heights of Fluvial Terraces","authors":"Masayoshi Tajikara, Y. Ikeda, T. Nohara","doi":"10.4294/ZISIN.62.1","DOIUrl":"https://doi.org/10.4294/ZISIN.62.1","url":null,"abstract":"The Iwate-Miyagi Nairiku Earthquake in 2008 occurred at June 14, 2008 in the area where active faults have not been mapped. We mapped fluvial terraces and measured the relative height between L1 and M1 surfaces around the source region of the Iwate-Miyagi Nairiku Earthquake, for the purpose of estimating location and nature of the source fault. Relative height between L1 and M1 surfaces is equivalent to amount of incision in the period between ages of L1 and M1 surfaces. We showed that amount of incision varies markedly around the focal region and that the variation of amount of incision is related to the activity of the Iwate-Miyagi Nairiku Earthquake in 2008. Difference of amount of incision between both sides of the source faults is about 60-65 meters. Assuming that incision and uplift are in balance, difference of incision is approximate to vertical displacement of the source fault. Supposing that L1 and M1 surfaces were formed in Marine Oxygen Isotope Stage 2 and 6, respectively, we can estimate the vertical displacement rate of the source fault at about 0.5 mm/yr. This value is similar to that of the Kitakami Lowland Western Margin Faults. We concluded that the location and nature of (blind) active fault can be estimated roughly even in areas with no clear fault scarp, by clarifying the distribution of amount of incision using heights of fluvial terraces.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"63 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128750081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Is the Assignment of JMA Seismic Intensity 5 at Sakura in Omaezaki City (Former Hamaoka) Due to the 1854 Ansei-Tokai Earthquake Appropriate from the Viewpoint of Historiographical Seismology?","authors":"K. Ishibashi","doi":"10.4294/ZISIN.62.13","DOIUrl":"https://doi.org/10.4294/ZISIN.62.13","url":null,"abstract":"","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125918096","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparison of Strong and Weak Ground Motion Characteristics Using Vertical Seismic Array Data —In the Case of Records during the 2007 Niigata-ken Chuetsu-oki Earthquake and Earthquakes before and after It at the Kashiwazaki-Kariwa Nuclear Power Plant Site—","authors":"Miho Kimura, K. Asano, T. Iwata","doi":"10.4294/ZISIN.62.61","DOIUrl":"https://doi.org/10.4294/ZISIN.62.61","url":null,"abstract":"","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"234 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133690948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Seismicity in the Seaward Slope of the Japan Trench, off Ibaraki, Using Ocean Bottom Seismometers for Long-term Observation","authors":"M. Mizuno, Toshinori Sato, M. Shinohara, K. Mochizuki, Tomoaki Yamada, T. Kanazawa","doi":"10.4294/ZISIN.62.19","DOIUrl":"https://doi.org/10.4294/ZISIN.62.19","url":null,"abstract":"","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123556854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stress Field in the Source Area of the 2004 Mid-Niigata Prefecture (Niigata-Chuetsu) Earthquake Inferred from Dense Aftershock Observation","authors":"M. Kosuga, Satoshi Iwabuchi, K. Murata","doi":"10.4294/ZISIN.62.27","DOIUrl":"https://doi.org/10.4294/ZISIN.62.27","url":null,"abstract":"We have investigated a stress field in the source region of the 2004 Mid-Niigata Prefecture (Niigata-Chuetsu) earthquake (M=6.8) by using P-wave polarity data obtained by a dense temporal seismic observation. The earthquake took place in central Japan near the eastern border of the Niigata-Kobe Tectonic Zone characterized by E-W contraction. The purpose of this study is to get insight into the stress heterogeneities in the source area including quite complex fault system with two parallel, westerly dipping fault planes and one conjugate plane. About two-thirds of well-constrained 514 focal mechanisms are reverse-fault type with WNW-ESE trending P-axes, which is consistent with the regional stress field in the area. Minor strike-slip events are distributed in the northern and central part of aftershock zone. Ten normal-fault events that are rare in the northeastern Japan are scattered mostly outside the major earthquake faults and occurred in a short period, suggesting that they reflect local stress field. Stress tensors derived from the focal mechanisms exhibit the compressional stress field characterized by nearly horizontal maximum principal stress that is consistent with the average direction of P-axes in the whole aftershock zone. Horizontal rotation of maximum principal stress axis is evident from WNW-ESE in the northeastern part of aftershock zone to E-W in the southwestern part. The direction of intermediate principle stress axis also changes from NE-SW in the northeastern part to NNE-SSW in the southwestern part. The fold axes in the area show similar strike variation. An interesting feature of stress distribution found in this study is the change in dip angle of the maximum principle stress axes. The axes through the aftershock zone dip gently to WNW, but those for earthquake clusters of mainshock fault dip steeply in a similar direction. Judging from the stress ratio, the horizontal compression is dominant near the mainshock hypocenter while the state in the surrounding areas is relatively close to isotropic stress. Though the difference in dip angle may not significant by considering the estimation error of stress axes, the combined anomalies with the stress ratio suggest that the mainshock occurred in an area of local stress inhomogeneity. We further examined the spatial distribution of earthquakes that have inconsistent focal mechanisms with the estimated stress tensors. Such earthquakes are distributed in the northeastern edge of the aftershock zone, in the southern edge of easterly dipping fault plane, and in a shallow earthquake cluster that is located between the faults of mainshock and the largest aftershock. The location of these events indicates small-scale stress heterogeneities in the source area superposed on the larger-scale stress variation mentioned above.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128718758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tomographic Evidence of Slab Subduction and Arc Magmatism in the Japan Subduction Zone","authors":"J. Nakajima, A. Hasegawa","doi":"10.4294/ZISIN.61.177","DOIUrl":"https://doi.org/10.4294/ZISIN.61.177","url":null,"abstract":"a dense nationwide seismograph network has been constructed in the Japanese Islands with an average station separation of ~ 20 km, which has produced the highest quality data in the world and contributed to enhance the understanding of seismotectonics and volcanotectonics there. Travel-time tomography using such high-quality data has provided two important constraints on water-transportation paths in subduction zones. One is the evidence for hydrous minerals in and immediately above the slab. The hydrated oceanic crust is imaged as a low-velocity layer to a depth of 40 km for the Philippine Sea slab and 70-130 km for the Pacific slab. Another low-velocity layer is revealed immediately above the Pacific slab down to a depth of ~110 km, which might correspond to a hydrous layer through which water is carried to deeper depths. The other is seismological imaging of mantle upwelling. Mantle return flows induced by the subduction of the Pacific and Philippine Sea slabs are imaged in Tohoku and Kyushu, respectively, whereas that probably generated by the subduction of both the Pacific and Philippine Sea slabs is apparent in central Japan. A large upwelling in the upper mantle revealed in the Chugoku district might be the origin of �uaternary volcanism there.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128331696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Intraslab Seismicity and its Generation Mechanisms","authors":"T. Seno","doi":"10.4294/ZISIN.61.357","DOIUrl":"https://doi.org/10.4294/ZISIN.61.357","url":null,"abstract":"History of studies of intraslab seismicity and its generation mechanisms, since the work by Wadati, is reviewed. Through the initial stage of studies of morphology of the intraslab seismicity, there followed the stage of discussion of focal mechanisms and terminal depths by mechanics and temperature of the slab. In 1970s, double seismic zones were discovered and their generation mechanisms were discussed in terms of bending or thermal stresses. In recent years, to overcome a difficulty that very high pressure prevents intraslab seismicity, dehydration embrittlement and phase transformation have been invoked for the mechanisms of intermediate and deep earthquakes, respectively. If the intermediate seismicity represents dehydration, it may give us a key to understand the distribution of fluids to the upper plate and to the seismogenic interplate thrusts, and finally to understand tectonics and volcanism in subduction zones.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129441867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Researches on Earthquake Source Processes and Tsunami Generation Using Tsunami Data","authors":"Y. Tanioka","doi":"10.4294/ZISIN.61.489","DOIUrl":"https://doi.org/10.4294/ZISIN.61.489","url":null,"abstract":"Studies in Japan on earthquake source processes and tsunami generation using tsunami data during recent 15 yeas are reviewed. The new tsunami observation systems including ocean bottom tsunami meters, GPS tsunami meters, and ultrasonic wave meters, have been developed recently. The methods using the tsunami waveform data observed by those advanced systems have also been developed and the detail source processes of the recent large earthquakes are studied using those methods and data. Studies on 2004 Sumatra-Andaman great earthquake, which caused the worst tsunami disaster and affected the countries around the Indian Ocean, are reviewed. Next, studies on source models of historical large earthquakes using tsunami data are reviewed. Researches on the mechanism of tsunami earthquakes are also reviewed. Finally, tsunami studies on submarine landslides triggered by earthquakes are reviewed.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129679830","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}