Journal of the Seismological Society of Japan最新文献

{"title":"Generation Mechanism of the Swarm Activity Following the 2004 Sumatra-Andaman Earthquake","authors":"S. Hiratsuka, Tamao Sato, N. Hurukawa","doi":"10.4294/ZISIN.64.33","DOIUrl":"https://doi.org/10.4294/ZISIN.64.33","url":null,"abstract":"A swarm activity occurred east off Nicobar Islands about a month after the 2004 Sumatra-Andaman earthquake. We discussed three issues related to the swarm activity, i.e., (1) How can the spatial distribution of strike-slip events and normal fault events be explained? (2) Why was the swarm activity triggered east off Nicobar Islands? (3) What is the mechanism of one month delay of the swarm activity? In order to address these issues, we relocated the hypocenters of the swarm activity using the Modifi ed Joint Hypocenter Determination (MJHD) method and investigated the spatial distribution of fault plane solutions. As a result, we found that the spatial distribution of strike-slip events and normal fault events can be explained by Riedel shears in the region between West Andaman Fault (WAF) and Sumatra Fault System (SFS). We calculated the spatial pattern of the change of the Coulomb Failure Function (ΔCFF) which suggests that the swarm activity was promoted by the coseismic slip and the afterslip of the Sumatra-Andaman earthquake. One month delay of the swarm activity may be explained by the upward migration of fl uid due to the change of bulk strain at the lower end of the mainshock fault.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"114 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128121125","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":"Atmospheric Pressure Waves Generated from Large Earthquakes, Tsunamis and Large Volcanic Eruptions","authors":"T. Mikumo","doi":"10.4294/ZISIN.64.47","DOIUrl":"https://doi.org/10.4294/ZISIN.64.47","url":null,"abstract":"This report reviews various studies on atmospheric pressure waves that have been generated from large earthquakes, tsunamis, and large-scale volcanic eruptions. These waves described here include low-frequency acoustic and gravity waves (0.0008∼0.0166 Hz or its period 1∼20 min) and high to medium frequency (› 0.0166 Hz or its period ‹ 1 min) infrasonic air-waves. The low-frequency acoustic-gravity waves came from coseismic vertical ground deformation associated with two megathrust earthquakes, and sometimes from other large earthquakes and volcanic eruptions, which propagated to more than several thousand kilometers through the lower to part of the upper atmosphere. The waves that reached the upper atmosphere could cause traveling ionospheric disturbances and perturbations of total electron content. The higher frequency infrasounds also have often been observed after large earthquakes and volcanic eruptions, which traveled as air-waves propagating directly from the source, and also as air-waves coupled with traveling seismic Rayleigh waves. Small atmospheric perturbations have also been detected during propagation of tsunami waves caused secondarily by large submarine earthquakes. Theoretical waveform modeling has been made in some of the above cases, incorporating a realistic atmospheric temperature structure. It is expected that more detailed information about the source process of large earthquakes and volcanic eruptions could be extracted through the analysis of the waveforms recorded at a number of stations, including their maximum amplitudes, wave frequencies, duration times, directions of wave approach, and phase and group velocities.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129383838","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":"Study on the Nonlinear Site Response Using the Green’s Functions of a Near-Surface Layer Estimated for Weak Motions","authors":"Y. Tanaka, S. Kinoshita","doi":"10.4294/ZISIN.63.197","DOIUrl":"https://doi.org/10.4294/ZISIN.63.197","url":null,"abstract":"Two noteworthy points shown in strong motion seismograms recently recorded in near source regions, are the transient response of tilt motion and the nonlinear response of near-surface layer. In the present study, we investigated the nonlinear response of near-surface layer by means of borehole array recordings. First, we estimated the Green’s function of near-surface layer for SH waves assuming that response of near-surface layer is linear for weak motion. Two Green’s functions are estimated for two different data sets which are constructed from the earthquakes occurred before the 2008 Iwate-Miyagi Inland Earthquake and its aftershocks, respectively. Furthermore, we estimated another Green’s function of near-surface layer using the coda part of the main shock of the 2008 Iwate-Miyagi Inland Earthquake. This Green’s function estimated using the coda part of main shock is signicantly different from the other two Green’s functions, although these two Green’s functions are practically identical. This fact reveals that the rigidity of surface layer reduced during the main shock and recovered after that. The coda part of main shock showed the reduced state of near-surface layer’s rigidity. Next, for explaining the strong motion part of main shock, we constructed a time-series model using the Green’s functions estimated using weak motion data. The nonlinear response of near-surface layer in the strong motion part is represented by the time-dependent pole conguration involving in the time-series model, which is constructed by an exponential auto-regressive model of second order. Hence, our constructed model is applicable to the whole process of main shock. Finally, we validated the practicability of model to the data involving the nonlinear response of near-surface layer by using borehole array recordings obtained at the IWTH25 station.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"34 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115645514","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":"Short-Period Seismic Wave Radiation Area and Magnitude of the 1914 Akita-Senboku Earthquake Inferred from Seismic Intensity Data by Comparison with the 1896 Rikuu Earthquake","authors":"K. Kanda, M. Takemura","doi":"10.4294/ZISIN.63.207","DOIUrl":"https://doi.org/10.4294/ZISIN.63.207","url":null,"abstract":"The 1914 Akita-Senboku earthquake was investigated using seismic intensity data estimated from damage records to clarify their magnitudes and source areas related to short-period seismic waves. We evaluated the most appropriate fault model of the Akita-Senboku earthquake on the basis of grid search analysis and other existing research works such as hypocenter distribution of micro earthquakes and S-wave velocity perturbations [Okada et al. (2010)]. The seismic intensity inversion analysis for the Akita-Senboku earthquake assuming an east-dipping fault model (depth: 6-13 km) indicated that the short-period radiation zone was located in the north and deep part of the fault plane and there was a low S-wave velocity zone in the lower crust beneath it. The magnitude of 6.5.6.6 yielded the least evaluation error. The magnitude was also estimated from the area of seismic intensity .ve-lower or more using empirical relationship [Muramatsu (1969)]. It resulted in M=6.6.∼6.7 and reinforced the accuracy of the intensity inversion result. It is concluded that the magnitude of the Akita-Senboku earthquake should be considerably less than M=7.1 after Utsu (1979) even if considering the estimation error. The 1896 Rikuu earthquake was also analyzed to be compared with the Akita-Senboku’s results and to consider their dieffrences. The fault location of the Rikuu earthquake was already identi.ed from surface faults. We assumed two conjugate faults for the northern fault zone of the eastern margin of the Mahiru mountains and the northern fault zone of the eastern margin of the Yokote basin. The most appropriate magnitude was estimated to be M=7.1, which is equivalent to that after Utsu (1979). Therefore, our results indicate that the Rikuu earthquake was considerably larger than the Akita-Senboku earthquake. The short-period radiation zone of the Rikuu earthquake, which might be less accurate due to the lack of intensity data compared to the Akita-Senboku earthquake, was located in shallow zone at the intersection of two conjugate faults. This location contrasts with that of the Akita-Senboku earthquake without surface faults.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"208 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114577285","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":"The Stone Memorial for Victims of the Ansei Nankai Earthquake Tsunami (1854)","authors":"T. Nagao","doi":"10.4294/ZISIN.63.251","DOIUrl":"https://doi.org/10.4294/ZISIN.63.251","url":null,"abstract":"1854 !\" #$% &' ( ) * +, . \" / /$ 01 ) * 23 4 5 6 . 7 8 9: ;< = > ? <; @A F \" G !H I\" #J= K\" 7LMH > N \" OP H Q \" RS TUVW$ XY !D E< =X=> Z[ B7\" E % 7 L MG CB !\" & (1999)7^_ B 'P$ (`\" )a *bcd e+f -gN;]) > ? ? !\" * 8 hi! %j k ,lm-n op.q/r st uv 0w1/n. N< = > ] GxCB &!\" y2 0 z{\" 3|]! g} G4P]~XNCB -g = 7\" % ! 2010 4 st u56v G€ l B‚\" ? G4P B (photo 1","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"11 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121840954","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":"The Comparison of Source Models of Repeating Subduction-zone Earthquakes Estimated Using Broadband Strong Motion Records","authors":"Masaharu Takiguchi, K. Asano, T. Iwata","doi":"10.4294/ZISIN.63.223","DOIUrl":"https://doi.org/10.4294/ZISIN.63.223","url":null,"abstract":"At the Ibaraki-ken-oki region where the Paci.c plate subducts beneath the North American plate, repeating M7 class subduction-zone earthquakes have occurred with an interval of approximately 21 years. We estimated the source rupture processes of two M7 Ibaraki-ken-oki earthquakes from broadband strong motion records and compared them to investigate the source characteristics of repeating subduction-zone earthquakes. First, the source model of MJ 7.0 earthquake occurring on May 8, 2008 (2008MS) was estimated by the forward modeling through strong motion simulations using the empirical Green’s function method. Strong ground motions were simulated in the broad.band frequency range (0.3-10 Hz). A single rectangular Strong Motion Generation Area (SMGA) was assumed. The synthetic waveforms at stations within 150 km from the hypocenter reproduced the observed ones well. Then, we estimated the source model of another MJ7.0 earthquake occurring on July 23, 1982 (1982MS). We compared the observed waveforms of the 1982MS and the 2008MS at the same stations and identi.ed the initial rupture phase for the 1982MS. We assumed a single rectangular SMGA away from the hypocenter of the 1982MS. The SMGA was located about 33 km westward from the hypocenter and ruptured about 11s after the origin time; this location was just 7 km northward to the 2008MS hypocenter and so inside its SMGA. We analyzed the spectral ratio of the strong motion records of the 1982MS to the 2008MS and estimated the size, stress drop, and slip amount of the SMGA of the 1982MS. The estimated size was the same as that of the 2008MS, but the stress drop and slip amount were approximately 1.5 times larger. Synthetic waveforms reproduced the observed ones well when we assumed the rupture propagation characteristics were the same as that of the 2008MS. This simulation did not have the resolution to several kilometers’change of the location of the SMGA. Our results indicate that the two SMGAs may overlap. They were the same size, but had different stress drops and slip amounts. The hypocentral locations and initial rupture processes were also different. These results show the variety of the repeating earthquakes occurring in this region.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131239064","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":"Relocation of Hypocenter Distribution in the Source Region of the 2008 Iwate-Miyagi Nairiku Earthquake before the Earthquake Occurrence","authors":"Kota Koshika, M. Oikawa, A. Hasemi","doi":"10.4294/ZISIN.63.247","DOIUrl":"https://doi.org/10.4294/ZISIN.63.247","url":null,"abstract":"","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128704201","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":"Nonlinear Soil Response and Its Effects on Strong Ground Motions during the 2003 Miyagi-Oki Intraslab Earthquake","authors":"S. Noguchi, T. Sasatani","doi":"10.4294/ZISIN.63.165","DOIUrl":"https://doi.org/10.4294/ZISIN.63.165","url":null,"abstract":"We investigate nonlinear soil responses based on strong motion records at a large number of observation sites during the 2003 Miyagi-oki intraslab earthquake (Mw 7.0). First, we examine the efficiency of S-H/V (horizontal-to-vertical spectral ratio for the S-wave portion at the ground surface) method to identify the nonlinearity by comparing the results with those by the standard S-wave surface-to-borehole spectral ratio method. In the examination we propose a new quantitative index to measure the degree of the nonlinear soil response, DNL, which evaluates the gap between the spectral ratio for strong ground motion and that for weak ground motion. The DNL values by the S-H/V method as well as those by the surface-to-borehole spectral ratio method increase with observed peak ground acceleration (PGA) values at surface (100∼1000 cm/s2), reflecting the increase of the degree of nonlinearity. However, both DNL values at sites with large S-wave velocity of the surface layer (>300 m/s) do not show any increase even for large PGA values (∼800 cm/s2), indicating linear site response. From these facts we conclude that the S-H/V spectral ratio method is also efficient to identify the nonlinearity. Second, in order to examine the effects of nonlinear soil response on strong ground motions, we make the broadband strong motion simulation for the 2003 Miyagi-oki earth.quake by means of the empirical Green’s function (EGF) method. The synthetic waveforms for the horizontal components at the ground surface significantly overestimate the observed ones at stations with large DNL values; the synthetic PGA values are about two times greater than the observed ones. We confirm that the overestimation is attributed to the ignorance of the nonlinear soil response in the EGF simulation. Finally we briefly discuss the potential of the DNL value for studying the nonlinear soil response.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"72 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129022179","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":"Simple Estimation Method of S-wave Velocity by Using One 3-Component Seismometer with P-wave Reflection Profiling","authors":"T. Ohtaki, N. Kano, T. Yokokura","doi":"10.4294/ZISIN.63.107","DOIUrl":"https://doi.org/10.4294/ZISIN.63.107","url":null,"abstract":"Seismic reflection profiling using P-to-SV converted waves with 3-component seismometers has an advantage for examining deeper S-wave velocity profile compared with other methods such as SH-wave reflection profiling. In spite of this advantage, the reflection profiling with 3-component seismometers has not been popular because it requires three-times more channels than reflection profiling with vertical-component seismometers, which is popular for examining P-wave velocity profile. In our previous paper, we showed a possibility of examining S-wave velocity profile by analyzing P-to-SV reflected waves observed at one 3-component seismometer together with P-wave reflection profiling. Although the method in the previous paper has ambiguity to obtain S-wave velocity, the approach is attractive because one additional 3-component seismometer requires little additional cost. In this paper, we show the validity of the approach using another method. This new method is easy to apply, if P-wave velocity profile was already determined using vertical component reflection profiling. We picked P-to-SV reflected waves on observed radial-component records, and adjusted theoretical travel-time curves to the observed waves at one 3-component seismometer. P-wave velocity profile and depths of discontinuities were fixed to the result of P-wave reflection profiling. When the travel time was calculated, a ratio of P-wave velocity to S-wave velocity was assumed to be the same for all layers. The ratio for well-matched theoretical time was considered as the ratio of vertical travel times of S-wave to P-wave from the surface to the reflected layer. Shear-wave velocity for each layer was calculated from the ratio. Slowness of the P-to-SV reflected wave at large offsets depends on P-wave velocity and a depth of the reflector, but shows little dependence on S-wave velocity at large offsets. This characteristic makes it possible to separate the influence of the reflector depth and of S-wave velocity on travel-time curves of the reflected waves. Tests for simple horizontal layer models and dipping layer models showed that S-wave velocities were obtained within about 10% in error, and that obtained S-wave velocity was stable in errors of P-wave velocity and of an inclination of the layer. We applied this method to a previous seismic reflection survey with 3-component seismometers which was carried out at Fuchu-city, Tokyo. Previous study analyzed P-and S-wave velocity profiles to 2-km depth using P-and converted-wave reflection profiling. Another survey also examined P-and S-wave velocity profiles near the survey line using VSP method. We selected one station near the VSP well among the survey stations, and analyzed the data using the method. S-wave velocity profile that we obtained was consistent with the profiles of the previous studies to 2-km depth. Only one 3-component seismometer was necessary for this method with P-wave reflection profiling. Our results show that this me","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"324 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124585398","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":"Crustal Structure in the Japanese Islands Inferred from Receiver Function Analysis","authors":"T. Igarashi, T. Iidaka, S. Miyabayashi","doi":"10.4294/ZISIN.63.139","DOIUrl":"https://doi.org/10.4294/ZISIN.63.139","url":null,"abstract":"Recently, several researchers have elucidated crustal structures over a large area of the Japanese Islands from travel time inversion analyses. However, very few studies have paid attention to velocity discontinuities due to the limitations of spatial resolution. In this study, we apply a receiver function analysis to estimate seismic velocity structure and seismic velocity discontinuities of the crust in the Japanese Islands. We search for the best-correlated velocity structure model between an observed receiver function at each station and synthetic ones using a grid search method. Synthetic receiver functions are calculated from many assumed simple velocity structures that consist of a sediment layer to compensate for the effects of the low-velocity sediment layer and two velocity discontinuities. As a result, we clarified the spatial distributions of the crustal S-wave velocities and the tops of mantle depths. Several plain and basin areas are covered with thick low-velocity sediment layers. There are low-velocity layers corresponding to volcanoes in the upper crust (5-15 km deep). In the lower crust (15-25 km deep), our results show low-velocity structures in the eastern part of the Niigata-Kobe Tectonic Zone (NKTZ) and the Median Tectonic Line. Around the crust-mantle boundary, we see clear low-velocity zones beneath volcanoes, the western part of the NKTZ, and in the occurrence regions of the non-volcanic low-frequency tremor. High velocities near the southern coastline of the Japanese Islands correspond to the crust-mantle discontinuity of the subducting Philippine Sea plate. The crustal structure beneath the Itoigawa-Shizuoka Tectonic Line (ISTL) shows relatively low velocities in the shallower part and high velocities in the deeper part compared to neighborhood areas. The ISTL is also the boundary of the velocity structure of the upper crust in the Japanese Islands. The northeastern Japan region has heterogeneities of velocity perturbations, whereas the southwestern Japan region has the relatively stable high-velocity zones. The tops of mantle depths tend to increase in mountain regions with some undulations. The discontinuity of the subducting Philippine Sea plate at a depth of more than 40 km is extracted in several areas from the Kanto district to the Kyushu district. This suggests that the velocity discontinuity of the subducting Philippine Sea plate is larger than that of the overriding plate.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2011-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126817832","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}