{"title":"Short History of the Rebeur-Paschwitz Tiltmeter Used in Kamigamo Observatory, Kyoto","authors":"S. Takemoto, J. Mori, L. Rivera, J. Fréchet","doi":"10.4294/ZISIN.63.45","DOIUrl":"https://doi.org/10.4294/ZISIN.63.45","url":null,"abstract":"","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121377919","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}
Y. Umeda, Kunihiro Shigetomi, Kensuke Onoue, Teruyuki Asada, Y. Hoso, K. Kondo, M. Hashimoto, Shozo Kimura, Kazuo Kawatani, M. Omura
The water level in wells along the Paci.c coast from the Kii peninsula to Shikoku showed remarkable decreases a few days before the 1946 Nankai earthquake. If pre-slip occurred on a deep portion of the earthquake fault, an uplift .eld would cover the area of the decreased well water. However, the expected uplift is only a few centimeters. Can the drastic changes of well water be explained by the slight uplift? By our field surveys, we confirmed that the wells were located in a small delta. The seawater permeates under the delta which faced the sea, and the fresh water .oats on the seawater due to the different density. The Ghyben-Herzberg’ law shows that the depth between the horizon and the sea-and fresh water boundary is balanced to 40 times of the height between the horizon and fresh water head which is called groundwater table. This law implies that a slight uplift of the fresh water in a delta induces a 40 times drop of the sea-and fresh water boundary. In this case, much fresh water will be required to suspend the slight uplift of fresh water. If the new fresh water does not be supplied from the outside of delta, the much fresh water flows from the upper level of delta to take the new balance. Then, the well water on the upper level of the delta must decrease or dry up. The decrease of well water before the great earthquake was also con.rmed at the time before the 1854 Nankai earthquake (M 8.4). The reproducibility of the decrease of well water level caused by the pre-slip of Nankai earthquakes is fairly high. These understandings are effective for the prediction of the next great Nankai earthquake.
{"title":"On the Well Water Decreases Preceded the Nankai Earthquake","authors":"Y. Umeda, Kunihiro Shigetomi, Kensuke Onoue, Teruyuki Asada, Y. Hoso, K. Kondo, M. Hashimoto, Shozo Kimura, Kazuo Kawatani, M. Omura","doi":"10.4294/ZISIN.63.1","DOIUrl":"https://doi.org/10.4294/ZISIN.63.1","url":null,"abstract":"The water level in wells along the Paci.c coast from the Kii peninsula to Shikoku showed remarkable decreases a few days before the 1946 Nankai earthquake. If pre-slip occurred on a deep portion of the earthquake fault, an uplift .eld would cover the area of the decreased well water. However, the expected uplift is only a few centimeters. Can the drastic changes of well water be explained by the slight uplift? By our field surveys, we confirmed that the wells were located in a small delta. The seawater permeates under the delta which faced the sea, and the fresh water .oats on the seawater due to the different density. The Ghyben-Herzberg’ law shows that the depth between the horizon and the sea-and fresh water boundary is balanced to 40 times of the height between the horizon and fresh water head which is called groundwater table. This law implies that a slight uplift of the fresh water in a delta induces a 40 times drop of the sea-and fresh water boundary. In this case, much fresh water will be required to suspend the slight uplift of fresh water. If the new fresh water does not be supplied from the outside of delta, the much fresh water flows from the upper level of delta to take the new balance. Then, the well water on the upper level of the delta must decrease or dry up. The decrease of well water before the great earthquake was also con.rmed at the time before the 1854 Nankai earthquake (M 8.4). The reproducibility of the decrease of well water level caused by the pre-slip of Nankai earthquakes is fairly high. These understandings are effective for the prediction of the next great Nankai earthquake.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"160 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115461555","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}
We studied the effect of body waves on short period vertical ground motion based on both a numerical simulation and field array observations. The vertical components generated by the vertical point force within a close distance are targeted throughout the study. Firstly, we carried out a numerical simulation and confirmed that the effect of body waves on the full-wave field was generally limited to a close distance from the source with frequency dependence. In a frequency range lower than 5 Hz and at around the 1st predominant frequency (5.8 Hz), the effect appears beyond a far distance; in a range of about 6 to 10 Hz, it still remains up to 10 m or more; in a range higher than 10 Hz, it almost vanishes. Secondly, we analyzed the observed array data excited by a 30-kg sandbag falling 10, 20, and 40 m from the array center. The array configuration was a circle, 1 m in radius, consisting of seven sensors placed in the center and around the circumference at equal intervals. To obtain a better understanding of the results of the array analyses, simulated array data, based on the Green's functions for the full-wave field and for the Rayleigh wave, was produced and analyzed in the same manner as the observed field array data. The phase velocity results were calculated with three different methods, namely, the spatial autocorrelation (SPAC) method, a method based on the spatial 1st Fourier coeffcients in the azimuthal direction with respect to the cross spectral amplitude between the center and one of circumferential stations, and a technique which combined these two methods. In the case of an offset of 10 m (Case 1), the detected phase velocities from the observed data and the simulated data on the full-wave field were much lower than the theoretical phase velocity or that from the Rayleigh wave array data in a frequency range of 5 to 10 Hz, suggesting the strong effect of body waves. In the case of an offset of 20 m (Case 2), the estimated phase velocities from the observed data and the two other simulated array data coincided with the theoretical phase velocity, suggesting the weak effect of body waves. We conclude that in order to properly estimate an underground structure from the array measurement data at a close distance from the source, the analytical technique based on the full-wave Green's function should be applied. Taking a look at the choice of analytical methods for the array data, it can be pointed out that for our interest the two methods which use the spatial 1st Fourier coeffcients produce higher accuracy compared with the SPAC method in a relatively low frequency range. In addition, the phase velocity results were estimated from the CCA (centerless circular array) method by Cho et al. (2004). The CCA method provided similar accuracy compared with the above two methods based on the spatial 1st Fourier coeffcients. The CCA method seems to be applicable to highly directional wave fields located nearby the source.
在数值模拟和场阵观测的基础上，研究了体波对短周期垂直地面运动的影响。在近距离范围内，垂直点力产生的垂直分量是整个研究的目标。首先，我们进行了数值模拟，证实了体波对全波场的影响一般限制在离震源较近的距离内，且具有频率依赖性。在低于5赫兹的频率范围内，在第一主频率(5.8赫兹)附近，这种效应出现在很远的距离之外;在约6至10赫兹的范围内，它仍然保持高达10米或更高;在高于10赫兹的范围内，它几乎消失。其次，我们分析了在距离阵列中心10、20和40 m处放置30 kg沙袋激发下的观测阵列数据。阵列配置是一个半径为1米的圆，由7个传感器组成，以相等的间隔放置在圆周的中心和周围。为了更好地理解阵列分析的结果，基于Green的全波场函数和瑞利波函数，以与观测到的场阵列数据相同的方式生成和分析了模拟阵列数据。采用空间自相关(SPAC)法、基于空间傅里叶系数在方位方向上相对于中心与周向站之间的交叉频谱幅值的方法以及两种方法相结合的方法计算相速度结果。在偏移10 m的情况下(案例1)，在5 ~ 10 Hz的频率范围内，观测数据和模拟数据在全波场上检测到的相速度远低于理论相速度或瑞利波阵列数据的相速度，表明体波的影响较强。在偏移20 m (case 2)的情况下，观测数据和另外两个模拟阵列数据的估计相速度与理论相速度一致，表明体波的影响较弱。我们认为，为了从近距离的阵列测量数据中正确估计地下结构，应采用基于全波格林函数的分析技术。看一下阵列数据分析方法的选择，可以指出，对于我们的兴趣，使用空间第一傅里叶系数的两种方法在相对较低的频率范围内比SPAC方法产生更高的精度。此外，Cho et al.(2004)利用CCA (centerless circular array)方法估算了相速度结果。与上述两种基于空间一阶傅里叶系数的方法相比，CCA方法具有相似的精度。CCA方法似乎适用于位于震源附近的高方向性波场。
{"title":"Analyses of Short-period Array Data Using a Full-wave Green's Function","authors":"M. Ohori, H. Morikawa, A. Nobata","doi":"10.4294/ZISIN.62.179","DOIUrl":"https://doi.org/10.4294/ZISIN.62.179","url":null,"abstract":"We studied the effect of body waves on short period vertical ground motion based on both a numerical simulation and field array observations. The vertical components generated by the vertical point force within a close distance are targeted throughout the study. Firstly, we carried out a numerical simulation and confirmed that the effect of body waves on the full-wave field was generally limited to a close distance from the source with frequency dependence. In a frequency range lower than 5 Hz and at around the 1st predominant frequency (5.8 Hz), the effect appears beyond a far distance; in a range of about 6 to 10 Hz, it still remains up to 10 m or more; in a range higher than 10 Hz, it almost vanishes. Secondly, we analyzed the observed array data excited by a 30-kg sandbag falling 10, 20, and 40 m from the array center. The array configuration was a circle, 1 m in radius, consisting of seven sensors placed in the center and around the circumference at equal intervals. To obtain a better understanding of the results of the array analyses, simulated array data, based on the Green's functions for the full-wave field and for the Rayleigh wave, was produced and analyzed in the same manner as the observed field array data. The phase velocity results were calculated with three different methods, namely, the spatial autocorrelation (SPAC) method, a method based on the spatial 1st Fourier coeffcients in the azimuthal direction with respect to the cross spectral amplitude between the center and one of circumferential stations, and a technique which combined these two methods. In the case of an offset of 10 m (Case 1), the detected phase velocities from the observed data and the simulated data on the full-wave field were much lower than the theoretical phase velocity or that from the Rayleigh wave array data in a frequency range of 5 to 10 Hz, suggesting the strong effect of body waves. In the case of an offset of 20 m (Case 2), the estimated phase velocities from the observed data and the two other simulated array data coincided with the theoretical phase velocity, suggesting the weak effect of body waves. We conclude that in order to properly estimate an underground structure from the array measurement data at a close distance from the source, the analytical technique based on the full-wave Green's function should be applied. Taking a look at the choice of analytical methods for the array data, it can be pointed out that for our interest the two methods which use the spatial 1st Fourier coeffcients produce higher accuracy compared with the SPAC method in a relatively low frequency range. In addition, the phase velocity results were estimated from the CCA (centerless circular array) method by Cho et al. (2004). The CCA method provided similar accuracy compared with the above two methods based on the spatial 1st Fourier coeffcients. The CCA method seems to be applicable to highly directional wave fields located nearby the source.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129109226","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}
K. Tamaribuchi, Yasuyuki Yamada, Y. Ishigaki, Yasunobu Takagi, Masaki Nakamura, K. Maeda, M. Okada
We found eight M 5.1 characteristic earthquakes regularly occurring since 1966 on the plate boundary between the Eurasian plate and the Philippine Sea plate near Miyakojima Island, the Ryukyu Arc, Japan. The quake recurrence interval was 5.89 years in average, and the standard deviation was only 0.73 years. The accumulating stress presumably ruptured the same asperity enclosed by the creeping zone repeatedly. Also, we found three other groups of small repeating earthquakes of M 4, which occurred close to the hypocenters of the M 5 events. Those groups also occurred regularly and we can consider them to be ‘characteristic’ earthquake sequences. Now, we called those groups A, B, and C. It is not clear whether groups A and B had an intrinsic recurrence interval or if they influenced each other. However, two events of group C occurred within one week after the M 5 quakes, indicating that the M 5 events triggered the group C events whose asperity had suffcient strain energy. No earthquake exceeding M 7, which could change the recurrence intervals, has been observed on the subduction zone around the Ryukyu Islands. Therefore, there should be numerous characteristic earthquake sequences in other areas of the Ryukyu district. We expect that the next M 5 earthquake at 50 km depth on the plate boundary near Miyakojima Island will occur between September 2012 and July 2014 with 70% probability, using the small-sample theory with a log-normal distribution model. Moreover, the M 5 event may be accompanied by an M 4 quake that could rupture the asperity of group C within one week.
{"title":"Characteristic Earthquake Sequences near Miyakojima Island, Ryukyu Arc, Japan","authors":"K. Tamaribuchi, Yasuyuki Yamada, Y. Ishigaki, Yasunobu Takagi, Masaki Nakamura, K. Maeda, M. Okada","doi":"10.4294/ZISIN.62.193","DOIUrl":"https://doi.org/10.4294/ZISIN.62.193","url":null,"abstract":"We found eight M 5.1 characteristic earthquakes regularly occurring since 1966 on the plate boundary between the Eurasian plate and the Philippine Sea plate near Miyakojima Island, the Ryukyu Arc, Japan. The quake recurrence interval was 5.89 years in average, and the standard deviation was only 0.73 years. The accumulating stress presumably ruptured the same asperity enclosed by the creeping zone repeatedly. Also, we found three other groups of small repeating earthquakes of M 4, which occurred close to the hypocenters of the M 5 events. Those groups also occurred regularly and we can consider them to be ‘characteristic’ earthquake sequences. Now, we called those groups A, B, and C. It is not clear whether groups A and B had an intrinsic recurrence interval or if they influenced each other. However, two events of group C occurred within one week after the M 5 quakes, indicating that the M 5 events triggered the group C events whose asperity had suffcient strain energy. No earthquake exceeding M 7, which could change the recurrence intervals, has been observed on the subduction zone around the Ryukyu Islands. Therefore, there should be numerous characteristic earthquake sequences in other areas of the Ryukyu district. We expect that the next M 5 earthquake at 50 km depth on the plate boundary near Miyakojima Island will occur between September 2012 and July 2014 with 70% probability, using the small-sample theory with a log-normal distribution model. Moreover, the M 5 event may be accompanied by an M 4 quake that could rupture the asperity of group C within one week.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128366099","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}
S. Toda, T. Maruyama, M. Yoshimi, H. Kaneda, Y. Awata, Toshikazu Yoshida, R. Ando
The Mjma 7.2 (Mw 6.9) Iwate-Miyagi Nairiku earthquake struck mountainous regions east of volcanic front in northern Honshu. To understand the relation between coseismic surface deformation and the seismogenic faulting and to have lessons in the long-term earthquake forecasting, we have performed urgent field investigations immediately after the main shock, while fragile structure and surface geomorphic features were fresh. More than 13 fault-rupture observations suggest that the estimated total length of the tectonic ground breakages reaches ∼20 km even though their locations are spotty rather than continuous along the entire trend. Contractional features such as thrust fault exposures, flexure, tilting, and buckling deformations predominate on the rupture zone, which is consistent with the reverse faulting under the WNW-ESE compressional stress field in northern Honshu. Such shortening features as well as vertical displacements were visible on cultural features such as concrete, asphalt paved roads, sidewalks, guardrails, drainage ditches, and rice paddies. Amounts of vertical offset and horizontal shortening measured using such cultural piercing points are mostly smaller than 50 cm (∼1 m of net slip). Fractures with such small slip, in turn, would not have been noticeable and may reflect the spotty distribution of the ruptures. Meanwhile, near the southern end of the rupture zone, fault structure and slip sense become complex and measured offsets are exceptionally large. We found a E-W-striking ∼1-km-long continuous rupture involved with 4-to-8-m dextral and 2-to-4-m vertical offsets of a paved road, trails, and rills near a massive giant landslide at the northern rim of the Aratozawa dam reservoir. Terrestrial LiDAR (Light Detection and Ranging) measurements together with our field observations reveal typical features of strike-slip faulting such as mole tracks, fissures, pressure ridges, bulges, and shutter ridges as well as the offset rills and ridges. Detail mapping of the ruptures suggests that this strike-slip dominant fault is a lateral ramp or tear fault that connects two distinct NNE-trending thrust faults, although we cannot rule out the possibility of a large mass movement due to gravitational force to induce such large displacements without suffcient geodetic and geologic data. The mapped zone of the ruptures approximately locates along the central part of the surface projection of a ∼40-km-long west-dipping source fault and associated aftershock zone. It also well corresponds to an asperity estimated from seismic and geodetic inversions, particularly southern end of the ground breakage zone. However, from the viewpoint of the long-term predictability, the surface fracturing occurred where none of active faults was previously mapped. Although several active geomorphic strands are likely to have reoccupied with the 2008 event, they are more spotty than the 2008 ruptures. Thus it would not have allowed us to properly evaluate size of
{"title":"Surface Rupture Associated with the 2008 Iwate-Miyagi Nairiku, Japan, Earthquake and its Implications to the Rupture Process and Evaluation of Active Faults","authors":"S. Toda, T. Maruyama, M. Yoshimi, H. Kaneda, Y. Awata, Toshikazu Yoshida, R. Ando","doi":"10.4294/ZISIN.62.153","DOIUrl":"https://doi.org/10.4294/ZISIN.62.153","url":null,"abstract":"The Mjma 7.2 (Mw 6.9) Iwate-Miyagi Nairiku earthquake struck mountainous regions east of volcanic front in northern Honshu. To understand the relation between coseismic surface deformation and the seismogenic faulting and to have lessons in the long-term earthquake forecasting, we have performed urgent field investigations immediately after the main shock, while fragile structure and surface geomorphic features were fresh. More than 13 fault-rupture observations suggest that the estimated total length of the tectonic ground breakages reaches ∼20 km even though their locations are spotty rather than continuous along the entire trend. Contractional features such as thrust fault exposures, flexure, tilting, and buckling deformations predominate on the rupture zone, which is consistent with the reverse faulting under the WNW-ESE compressional stress field in northern Honshu. Such shortening features as well as vertical displacements were visible on cultural features such as concrete, asphalt paved roads, sidewalks, guardrails, drainage ditches, and rice paddies. Amounts of vertical offset and horizontal shortening measured using such cultural piercing points are mostly smaller than 50 cm (∼1 m of net slip). Fractures with such small slip, in turn, would not have been noticeable and may reflect the spotty distribution of the ruptures. Meanwhile, near the southern end of the rupture zone, fault structure and slip sense become complex and measured offsets are exceptionally large. We found a E-W-striking ∼1-km-long continuous rupture involved with 4-to-8-m dextral and 2-to-4-m vertical offsets of a paved road, trails, and rills near a massive giant landslide at the northern rim of the Aratozawa dam reservoir. Terrestrial LiDAR (Light Detection and Ranging) measurements together with our field observations reveal typical features of strike-slip faulting such as mole tracks, fissures, pressure ridges, bulges, and shutter ridges as well as the offset rills and ridges. Detail mapping of the ruptures suggests that this strike-slip dominant fault is a lateral ramp or tear fault that connects two distinct NNE-trending thrust faults, although we cannot rule out the possibility of a large mass movement due to gravitational force to induce such large displacements without suffcient geodetic and geologic data. The mapped zone of the ruptures approximately locates along the central part of the surface projection of a ∼40-km-long west-dipping source fault and associated aftershock zone. It also well corresponds to an asperity estimated from seismic and geodetic inversions, particularly southern end of the ground breakage zone. However, from the viewpoint of the long-term predictability, the surface fracturing occurred where none of active faults was previously mapped. Although several active geomorphic strands are likely to have reoccupied with the 2008 event, they are more spotty than the 2008 ruptures. Thus it would not have allowed us to properly evaluate size of ","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128077663","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}
一柳 昌義, 高橋 浩晃, 前田 宜浩, 笠原 稔, 宮町 宏樹, 平野 舟一郎, Sen Rak Se, M. Valentin, Kim Chun Ung
On August 2, 2007, an MJMA 6.4 moderate earthquake occurred off the southwest coast of Sakhalin Island, far eastern Russia. In the city of Nevelsk, situated just in the aftershock region, two people were killed and more than 240 buildings were damaged (we call this event as the 2007 Nevelsk earthquake). We have operated a temporal seismological network in southern Sakhalin consisted in ten stations with short-period sensors and 16-bit recorders since 2003. This dense network well recorded this earthquake and the following aftershock sequence. Initial aftershock hypocenters were calculated using a 1-D P-wave velocity structure that was estimated from 746 P-wave arrival times, including data from the aftershocks. To obtain a more precise aftershock distribution, we applied a double-difference hypocenter determination method. The well-determined aftershock hypocenters shows the following features; (1) in the northern and central parts of aftershock region, epicenters were distributed in the sea along the coast with NE-SW direction, (2) while in the southern part of aftershock region trend of epicenters changed toward land with NNW-SSE direction. This southern most part intersects the city of Nevelsk where severe damage occurred. On August 17, 2006, the 2006 Gomozavodskoe earthquake (MJMA 5.9) occurred near the southeastward aftershock region of the 2007 Nevelsk earthquake. The 2006 earthquake sequence was occurred deeper area as compared to the 2007 event. We examine the change in Coulomb failure function produced by the 2006 event and conclude that the 2006 event has less influence on occurrence of the 2007 event.
{"title":"日露共同地震観測による2007年8月2日に発生したサハリン南西沖の地震(M_ 6.4)の余震活動","authors":"一柳 昌義, 高橋 浩晃, 前田 宜浩, 笠原 稔, 宮町 宏樹, 平野 舟一郎, Sen Rak Se, M. Valentin, Kim Chun Ung","doi":"10.4294/ZISIN.62.139","DOIUrl":"https://doi.org/10.4294/ZISIN.62.139","url":null,"abstract":"On August 2, 2007, an MJMA 6.4 moderate earthquake occurred off the southwest coast of Sakhalin Island, far eastern Russia. In the city of Nevelsk, situated just in the aftershock region, two people were killed and more than 240 buildings were damaged (we call this event as the 2007 Nevelsk earthquake). We have operated a temporal seismological network in southern Sakhalin consisted in ten stations with short-period sensors and 16-bit recorders since 2003. This dense network well recorded this earthquake and the following aftershock sequence. Initial aftershock hypocenters were calculated using a 1-D P-wave velocity structure that was estimated from 746 P-wave arrival times, including data from the aftershocks. To obtain a more precise aftershock distribution, we applied a double-difference hypocenter determination method. The well-determined aftershock hypocenters shows the following features; (1) in the northern and central parts of aftershock region, epicenters were distributed in the sea along the coast with NE-SW direction, (2) while in the southern part of aftershock region trend of epicenters changed toward land with NNW-SSE direction. This southern most part intersects the city of Nevelsk where severe damage occurred. On August 17, 2006, the 2006 Gomozavodskoe earthquake (MJMA 5.9) occurred near the southeastward aftershock region of the 2007 Nevelsk earthquake. The 2006 earthquake sequence was occurred deeper area as compared to the 2007 event. We examine the change in Coulomb failure function produced by the 2006 event and conclude that the 2006 event has less influence on occurrence of the 2007 event.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2010-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124300569","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}
K. Asano, T. Iwata, A. Iwaki, M. Kuriyama, W. Suzuki
During the 2007 Noto Hanto earthquake, a K-NET station ISK005, which is located in Anamizu town and approximately 19 km far from the epicenter, recorded the ground velocity larger than 100 cm/s. A set of observational study is carried out to investigate spatial variation of ground motion amplification characteristics in Anamizu town. Firstly, the spatial variation of the amplification was observed by aftershock observations along a temporary linear seismic array across Anamizu town. In the center of the town, the spectral amplification factor is 10 to 20 between 1 Hz and 2 Hz with respect to the rock site. Then, dense single-station microtremor observations were carried out at 147 sites with average spacing of 100 m in Anamizu town to see the spatial variation in thickness of low-velocity layers. The peak frequency of the microtremor H/V spectral ratio varies from 0.8 to 2.0 Hz in the town. The velocity structure model of shallow portion in Anamizu town is estimated from the mircrotremor H/V spectral ratios. The thickness of low-velocity layers (VS =70 to 100 m/s) changes along the Omata and the Manai rivers. Finally, a three-dimensional ground motion simulation is conducted using the obtained velocity structure model in order to see relationship between shallow sedimentary layers and ground motion amplification in Anamizu town. The peak velocity in the frequency range below 2.5 Hz is three or four times larger in the area around ISK005, where the thickness of low-velocity layers is approximately 10 to 25 m, than that in the rock side. It could be concluded that the ground motion amplification characteristics in the frequency range between 1 Hz and 2 Hz is mainly controlled by the existence of such low-velocity sedimentary layers.
{"title":"Ground Motion Characteristics in Anamizu Town Obtained from Earthquake and Microtremor Observations","authors":"K. Asano, T. Iwata, A. Iwaki, M. Kuriyama, W. Suzuki","doi":"10.4294/ZISIN.62.121","DOIUrl":"https://doi.org/10.4294/ZISIN.62.121","url":null,"abstract":"During the 2007 Noto Hanto earthquake, a K-NET station ISK005, which is located in Anamizu town and approximately 19 km far from the epicenter, recorded the ground velocity larger than 100 cm/s. A set of observational study is carried out to investigate spatial variation of ground motion amplification characteristics in Anamizu town. Firstly, the spatial variation of the amplification was observed by aftershock observations along a temporary linear seismic array across Anamizu town. In the center of the town, the spectral amplification factor is 10 to 20 between 1 Hz and 2 Hz with respect to the rock site. Then, dense single-station microtremor observations were carried out at 147 sites with average spacing of 100 m in Anamizu town to see the spatial variation in thickness of low-velocity layers. The peak frequency of the microtremor H/V spectral ratio varies from 0.8 to 2.0 Hz in the town. The velocity structure model of shallow portion in Anamizu town is estimated from the mircrotremor H/V spectral ratios. The thickness of low-velocity layers (VS =70 to 100 m/s) changes along the Omata and the Manai rivers. Finally, a three-dimensional ground motion simulation is conducted using the obtained velocity structure model in order to see relationship between shallow sedimentary layers and ground motion amplification in Anamizu town. The peak velocity in the frequency range below 2.5 Hz is three or four times larger in the area around ISK005, where the thickness of low-velocity layers is approximately 10 to 25 m, than that in the rock side. It could be concluded that the ground motion amplification characteristics in the frequency range between 1 Hz and 2 Hz is mainly controlled by the existence of such low-velocity sedimentary layers.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124180000","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}
Long-term slow slip events with the recurrence period of about 10-30 years have been observed beneath Lake Hamana in the Tokai district where historically great interplate earthquakes occurred repeatedly. We intend to simulate the recurrent slow slip events before the occurrence of cyclic great earthquakes using a three-dimensional earthquake cycle model based on the rate- and state-dependent friction law with heterogeneous friction parameters on the plate interface. In our model we can simulate recurring slow slip events with the period of about 30-40 years near beneath Lake Hamana, by applying small negative values to frictional parameter (a-b)and small values to characteristic distance L for the western region of the Tokai district, and large values to L for the regions off Tokai district where seismic structure surveys reveal the existence of a subducting ridge.
{"title":"An Attempt at Simulation of Long Term Slow Slip Events and Seismic Cycle in the Tokai Region","authors":"F. Hirose, K. Maeda, H. Takayama","doi":"10.4294/ZISIN.62.67","DOIUrl":"https://doi.org/10.4294/ZISIN.62.67","url":null,"abstract":"Long-term slow slip events with the recurrence period of about 10-30 years have been observed beneath Lake Hamana in the Tokai district where historically great interplate earthquakes occurred repeatedly. We intend to simulate the recurrent slow slip events before the occurrence of cyclic great earthquakes using a three-dimensional earthquake cycle model based on the rate- and state-dependent friction law with heterogeneous friction parameters on the plate interface. In our model we can simulate recurring slow slip events with the period of about 30-40 years near beneath Lake Hamana, by applying small negative values to frictional parameter (a-b)and small values to characteristic distance L for the western region of the Tokai district, and large values to L for the regions off Tokai district where seismic structure surveys reveal the existence of a subducting ridge.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"91 9 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131231787","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}
We investigate the shallow subsurface S-wave velocity structure across the Kego fault at the area of Tenjin in Chuo Ward, Fukuoka, Japan. We observed microtremors for several minutes by small arrays consisting of 7 sensors at 8 sites using wireless LAN data loggers. These sites were situated at the same locations of observation sites by Yamanaka et al. (2005) for aftershocks of the 2005 north-west off Fukuoka prefecture MJ 7.0 earthquake and with K-NET station FKO006. The micro-tremor array data were processed to obtain Rayleigh wave phase velocities in the period range of 0.04-0.4 s by SPAC analysis. Then the 1D S-wave velocity structures having three layers with a Vs of about 130-170 m/s, 220-260 m/s and 800 m/s are estimated from hybrid inversions at each site. The depth to the top of the layer of Vs 800 m/s is only 5 m at the site west of the Kego fault, while the depth is 25-40 m at the sites east of the fault. The layer with a Vs of 800 m/s has a steep slope with a thickness difference of about 20 m at the fault. These 1D velocity structure models show amplifica-tions characterized by dominant peaks in period range of longer than 0.2 s. However, the distribution of the AVS30s for the profiles shows no correlation to those of the ratios of PGA and PGV and the difference of seismic intensity. This indicates the limit of understanding only by 1D structure model and necessity of the consideration of 2D or 3D subsurface structure. The profile for FKO006 at site 08 is different from previous study, which has a deeper depth of the top of the engineering bedrock in our model. These results must be included to explain the observed strong ground motion records of the 2005 earthquake around the central Fukuoka area in short period range.
{"title":"Subsurface S-Wave Velocity Structure at Tenjin Area in Chuo Ward, Fukuoka City","authors":"N. Yamada, H. Yamanaka, K. Motoki","doi":"10.4294/ZISIN.62.109","DOIUrl":"https://doi.org/10.4294/ZISIN.62.109","url":null,"abstract":"We investigate the shallow subsurface S-wave velocity structure across the Kego fault at the area of Tenjin in Chuo Ward, Fukuoka, Japan. We observed microtremors for several minutes by small arrays consisting of 7 sensors at 8 sites using wireless LAN data loggers. These sites were situated at the same locations of observation sites by Yamanaka et al. (2005) for aftershocks of the 2005 north-west off Fukuoka prefecture MJ 7.0 earthquake and with K-NET station FKO006. The micro-tremor array data were processed to obtain Rayleigh wave phase velocities in the period range of 0.04-0.4 s by SPAC analysis. Then the 1D S-wave velocity structures having three layers with a Vs of about 130-170 m/s, 220-260 m/s and 800 m/s are estimated from hybrid inversions at each site. The depth to the top of the layer of Vs 800 m/s is only 5 m at the site west of the Kego fault, while the depth is 25-40 m at the sites east of the fault. The layer with a Vs of 800 m/s has a steep slope with a thickness difference of about 20 m at the fault. These 1D velocity structure models show amplifica-tions characterized by dominant peaks in period range of longer than 0.2 s. However, the distribution of the AVS30s for the profiles shows no correlation to those of the ratios of PGA and PGV and the difference of seismic intensity. This indicates the limit of understanding only by 1D structure model and necessity of the consideration of 2D or 3D subsurface structure. The profile for FKO006 at site 08 is different from previous study, which has a deeper depth of the top of the engineering bedrock in our model. These results must be included to explain the observed strong ground motion records of the 2005 earthquake around the central Fukuoka area in short period range.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"52 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132767557","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}
This study reexamines the ground deformation and fault slip model of the 1945 Mikawa earthquake (M =6.8), central Japan. We reevaluate two geodetic data sets from the years 1886/1887 and 1955/56 that were obtained from the Geographical Survey Institute; these data sets consist of displacements calculated from the net adjustment of triangulation surveys carried out before and after the Mikawa earthquake. We remove the interseismic deformation and coseismic deformation of the 1944 Tonankai earthquake from the two unique data sets used in our analysis. Maximum coseismic horizontal displacements of over 1.4 m were detected to the west of the Fukozu fault. We estimated the coseismic slip by analyzing our data set. The geometry of the fault planes was adopted from a recent seismicity study and from the surface earthquake fault of this area. The best fit to the data is obtained from two faults along the sections running north and south of the Fukozu and Yokosuka faults. The estimated uniform-slip elastic dislocation model consists of two adjacent planes. The fault also appeared to connect the sections running north and south of the Fukozu and Yokosuka faults. Because it can suitably explain the coseismic deformation due to two earthquake source faults, the earthquake source fault is not admitted under the section for the run. The mechanism is considered to be two reverse faults with right-lateral components. The estimated slips for the two source faults are 2.5 m and 1.4 m, respectively. The pressure axis is directed along NE-SW or E-W. The total seismic moment determined from this model is 1.6 × 1019 Nm, corresponding to Mw=6.7.
{"title":"Re-examination of Ground Deformation and Fault Models of the 1945 Mikawa Earthquake (M =6.8)","authors":"K. Takano, F. Kimata","doi":"10.4294/ZISIN.62.85","DOIUrl":"https://doi.org/10.4294/ZISIN.62.85","url":null,"abstract":"This study reexamines the ground deformation and fault slip model of the 1945 Mikawa earthquake (M =6.8), central Japan. We reevaluate two geodetic data sets from the years 1886/1887 and 1955/56 that were obtained from the Geographical Survey Institute; these data sets consist of displacements calculated from the net adjustment of triangulation surveys carried out before and after the Mikawa earthquake. We remove the interseismic deformation and coseismic deformation of the 1944 Tonankai earthquake from the two unique data sets used in our analysis. Maximum coseismic horizontal displacements of over 1.4 m were detected to the west of the Fukozu fault. We estimated the coseismic slip by analyzing our data set. The geometry of the fault planes was adopted from a recent seismicity study and from the surface earthquake fault of this area. The best fit to the data is obtained from two faults along the sections running north and south of the Fukozu and Yokosuka faults. The estimated uniform-slip elastic dislocation model consists of two adjacent planes. The fault also appeared to connect the sections running north and south of the Fukozu and Yokosuka faults. Because it can suitably explain the coseismic deformation due to two earthquake source faults, the earthquake source fault is not admitted under the section for the run. The mechanism is considered to be two reverse faults with right-lateral components. The estimated slips for the two source faults are 2.5 m and 1.4 m, respectively. The pressure axis is directed along NE-SW or E-W. The total seismic moment determined from this model is 1.6 × 1019 Nm, corresponding to Mw=6.7.","PeriodicalId":332254,"journal":{"name":"Journal of the Seismological Society of Japan","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134502202","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}
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