DSpace Collection: 2009-03-15
http://hdl.handle.net/2115/38140
2009-03-152024-03-29T01:18:41Z中千島で発生した巨大地震
http://hdl.handle.net/2115/38170
Title: 中千島で発生した巨大地震
Authors: 高橋, 浩晃; 前田, 宜浩; 笠原, 稔
Abstract: We investigate the characteristics of great earthquakes occurring in the central Kuril Islands on 1915, 1918, 2006 and 2007. Comparisons of seismic intensity distributions, tsunami data and waveforms of above four events were made. Though magnitudes of these earthquakes were almost the same, only the 1915 event did not generate observable tsunami. This fact may be due to deep focal depth of this earthquake. Similarities of seismic intensity distributions between the 1915, 1971 and 2008 deep-focus earthquakes also imply that the 1915 event was the deep-focus event in the northeastern Okhotsk Sea. Waveform properties of the 1915 and 2008 events supports above hypothesis. We conclude, therefore, that the 1915 earthquake was not the event in the central Kuril Island but in the Okhotsk Sea with deep depth. Large tsunami and widespread felt area of the 1918 earthquake show that this event was a typical shallow-dipping thrust event on plate boundary as indicated by previous studies.2009-03-14T15:00:00Z高橋, 浩晃前田, 宜浩笠原, 稔We investigate the characteristics of great earthquakes occurring in the central Kuril Islands on 1915, 1918, 2006 and 2007. Comparisons of seismic intensity distributions, tsunami data and waveforms of above four events were made. Though magnitudes of these earthquakes were almost the same, only the 1915 event did not generate observable tsunami. This fact may be due to deep focal depth of this earthquake. Similarities of seismic intensity distributions between the 1915, 1971 and 2008 deep-focus earthquakes also imply that the 1915 event was the deep-focus event in the northeastern Okhotsk Sea. Waveform properties of the 1915 and 2008 events supports above hypothesis. We conclude, therefore, that the 1915 earthquake was not the event in the central Kuril Island but in the Okhotsk Sea with deep depth. Large tsunami and widespread felt area of the 1918 earthquake show that this event was a typical shallow-dipping thrust event on plate boundary as indicated by previous studies.MT法による黒松内地域の地下構造
http://hdl.handle.net/2115/38169
Title: MT法による黒松内地域の地下構造
Authors: 平田, 貴一; 茂木, 透; 山谷, 祐介; 長谷, 英彰; 市原, 寛
Abstract: A magnetotelluric (MT) survey was conducted in the Kuromatsunai area to identify resistivity structures and their features. A basin that formed in the Kuromatsunai lowland area during the Miocene contains a thick Miocene to Plio-Pleistocene sediments. On the west side of the lowland is an active fault zone that is experiencing ongoing, east-down displacement. Three magnetic field components and two horizontal electrical field components were observed over 20-40 hours at eleven sites, and magnetotelluric impedances were calculated for a frequency range of 320-0.00034 Hz. The strike direction of dominant resistivity structures was determined using a phase tensor estimation (Caldwell et al., 2004). A two-dimensional resistivity structure was obtained through a two-dimensional inversion with smoothness constraints and static shift corrections (Ogawa and Uchida, 1996). The results show that relatively resistive Plio-Pleistocene to upper Miocene strata occupy the shallow subsurface of the lowland. Conductive lower to middle Miocene strata underlie the Plio-Pleistocene units. Resistive granitic rocks present at greater depth below the lowland differ from the material present at similar depth outside of the lowland area. Granitic rocks are also exposed at the eastern end of the lowland. Induction vectors observed in the MT survey at Komagatake Volcano (Yamaya et al., 2004) suggest that telluric current flows toward the Japan Sea from the Pacific side of Funka Bay through a conductive layer at the back of the bay. It is likely that this conductive unit corresponds to the thick Miocene strata of the Kuromatsunai area.2009-03-14T15:00:00Z平田, 貴一茂木, 透山谷, 祐介長谷, 英彰市原, 寛A magnetotelluric (MT) survey was conducted in the Kuromatsunai area to identify resistivity structures and their features. A basin that formed in the Kuromatsunai lowland area during the Miocene contains a thick Miocene to Plio-Pleistocene sediments. On the west side of the lowland is an active fault zone that is experiencing ongoing, east-down displacement. Three magnetic field components and two horizontal electrical field components were observed over 20-40 hours at eleven sites, and magnetotelluric impedances were calculated for a frequency range of 320-0.00034 Hz. The strike direction of dominant resistivity structures was determined using a phase tensor estimation (Caldwell et al., 2004). A two-dimensional resistivity structure was obtained through a two-dimensional inversion with smoothness constraints and static shift corrections (Ogawa and Uchida, 1996). The results show that relatively resistive Plio-Pleistocene to upper Miocene strata occupy the shallow subsurface of the lowland. Conductive lower to middle Miocene strata underlie the Plio-Pleistocene units. Resistive granitic rocks present at greater depth below the lowland differ from the material present at similar depth outside of the lowland area. Granitic rocks are also exposed at the eastern end of the lowland. Induction vectors observed in the MT survey at Komagatake Volcano (Yamaya et al., 2004) suggest that telluric current flows toward the Japan Sea from the Pacific side of Funka Bay through a conductive layer at the back of the bay. It is likely that this conductive unit corresponds to the thick Miocene strata of the Kuromatsunai area.文禄五年 (1596) 閏七月豊後・伊予地震による伊予国板島城 (現宇和島城) の被害 : 藤堂虎高の遺帖
http://hdl.handle.net/2115/38168
Title: 文禄五年 (1596) 閏七月豊後・伊予地震による伊予国板島城 (現宇和島城) の被害 : 藤堂虎高の遺帖
Authors: 中西, 一郎
Abstract: A record is found in the historical document of the Toudou family in relation to the 1596 Bungo-Iyo earthquake. The document was written about 180 years after the occurrence of the earthquake. The record shows that the castle Uwajima was damaged by the 1596 earthquake and provides us with an important constraint on the location of the earthquake.2009-03-14T15:00:00Z中西, 一郎A record is found in the historical document of the Toudou family in relation to the 1596 Bungo-Iyo earthquake. The document was written about 180 years after the occurrence of the earthquake. The record shows that the castle Uwajima was damaged by the 1596 earthquake and provides us with an important constraint on the location of the earthquake.巨大遠地地震による長周期歪地震波形の解析 : 2004年Sumatra-Andaman地震 (Mw9.0) 及び2005年Nias地震 (Mw8.6)
http://hdl.handle.net/2115/38167
Title: 巨大遠地地震による長周期歪地震波形の解析 : 2004年Sumatra-Andaman地震 (Mw9.0) 及び2005年Nias地震 (Mw8.6)
Authors: 上垣, 拓郎; 池上, 裕; 中西, 一郎; 小久保, 一哉; 露木, 貴裕; 中村, 浩二; 原田, 智史
Abstract: The long-period strain seismograms from the Sumatra-Andaman earthquake of December 26, 2004 and the Nias earthquake of March 28, 2005 are analyzed by comparing the observed seismograms with synthetic seismograms calculated by normal mode theory. The multiple CMT source (Tsai et al., 2005) and Harvard CMT solution explain the seismograms recorded by both extensometers and volumetric strainmeters from the 2004 and 2005 earthquakes, respectively. The long-period strain seismograms observed in Japan are consistent with about 9 min source duration and 1200 km fault length proposed by Tsai et al. (2005) and Velasco et al. (2006).2009-03-14T15:00:00Z上垣, 拓郎池上, 裕中西, 一郎小久保, 一哉露木, 貴裕中村, 浩二原田, 智史The long-period strain seismograms from the Sumatra-Andaman earthquake of December 26, 2004 and the Nias earthquake of March 28, 2005 are analyzed by comparing the observed seismograms with synthetic seismograms calculated by normal mode theory. The multiple CMT source (Tsai et al., 2005) and Harvard CMT solution explain the seismograms recorded by both extensometers and volumetric strainmeters from the 2004 and 2005 earthquakes, respectively. The long-period strain seismograms observed in Japan are consistent with about 9 min source duration and 1200 km fault length proposed by Tsai et al. (2005) and Velasco et al. (2006).巨大近地地震による長周期体積歪波形の解析 : 2006年及び2007年千島列島地震 (Mw8.3及び8.1) と津波
http://hdl.handle.net/2115/38166
Title: 巨大近地地震による長周期体積歪波形の解析 : 2006年及び2007年千島列島地震 (Mw8.3及び8.1) と津波
Authors: 上垣, 拓郎; 中西, 一郎; 露木, 貴裕; 原田, 智史
Abstract: The Kurile Islands earthquakes of November 15, 2006 and January 13, 2007 are studied by using the volumetric strainmeter array in Tokai-Kanto area, Japan. The first-motion of long-period P waves recorded by the array shows good correlation with the first-arrival of tsunami waves observed on the Pacific side of Japan. The amplitude ratio of the long-period P waves (T > 50 s) between the two earthquakes explains the difference in moment magnitudes. The inconsistency between moment magnitudes and JMA magnitudes of the two earthquakes may have been caused by the difference of phases and period ranges used in the determination of the two magnitudes.2009-03-14T15:00:00Z上垣, 拓郎中西, 一郎露木, 貴裕原田, 智史The Kurile Islands earthquakes of November 15, 2006 and January 13, 2007 are studied by using the volumetric strainmeter array in Tokai-Kanto area, Japan. The first-motion of long-period P waves recorded by the array shows good correlation with the first-arrival of tsunami waves observed on the Pacific side of Japan. The amplitude ratio of the long-period P waves (T > 50 s) between the two earthquakes explains the difference in moment magnitudes. The inconsistency between moment magnitudes and JMA magnitudes of the two earthquakes may have been caused by the difference of phases and period ranges used in the determination of the two magnitudes.雲仙火山周辺域における相対応力場と1990-1995年噴火活動
http://hdl.handle.net/2115/38165
Title: 雲仙火山周辺域における相対応力場と1990-1995年噴火活動
Authors: 河野, 裕希; 松本, 聡; 松島, 健; 植平, 賢司; 清水, 洋; 馬越, 孝道
Abstract: We investigated a stress field around the magma chamber beneath Unzen Volcano, Kyushu, Japan, which erupted from 1990 until 1995, by using a stress-tensor inversion method. We used P wave polarity data of seismograms by earthquakes occurred during 1985-1999 for analysis. Our result clearly indicated that there were no changes in stress field during the period except for during 1986-1988. This suggested that the magma intrusion into shallower depths did not affect the stress field in this region. Clear change in stress field was observed during 1986-1988. This might be explained by applying the meshtexture crack model proposed by Hill (1977).2009-03-14T15:00:00Z河野, 裕希松本, 聡松島, 健植平, 賢司清水, 洋馬越, 孝道We investigated a stress field around the magma chamber beneath Unzen Volcano, Kyushu, Japan, which erupted from 1990 until 1995, by using a stress-tensor inversion method. We used P wave polarity data of seismograms by earthquakes occurred during 1985-1999 for analysis. Our result clearly indicated that there were no changes in stress field during the period except for during 1986-1988. This suggested that the magma intrusion into shallower depths did not affect the stress field in this region. Clear change in stress field was observed during 1986-1988. This might be explained by applying the meshtexture crack model proposed by Hill (1977).ALOS/PALSARによって観測された,アリューシャン列島・Okmok火山における2008年噴火
http://hdl.handle.net/2115/38164
Title: ALOS/PALSARによって観測された,アリューシャン列島・Okmok火山における2008年噴火
Authors: 宮城, 洋介
Abstract: On July 12 (UTC), 2008, Okmok volcano in the Aleutian Islands began to erupt after a lapse of 11 years. Okmok volcano is located on Umnak Island in the Aleutian volcanic chain, and has erupted from an active vent located in the southwest part of the caldera floor more than 10 times since 19th century. Although there are few habitants around Okmok volcano, ash from the eruption could lead to catastrophic airplane accidents because of the heavy air traffic over the Aleutian Islands. In the 2008 event, ash plumes were emitted up to 15,000m above sea level from the new vent located close to the caldera center, not the active vent. JAXA carried out several observations using ALOS/PALSR before and after the eruption. PALSAR can observe the volcano surface even if it is emitting a great deal of smoke. Comparing images acquired before and after the eruption, we detected surface changes on and around the Okmok caldera and could locate new vents in the area close to the caldera center. Using DInSAR technique of PALSAR data acquired after the eruption, we detected a deflation of the volcanic edifice for the period at least one and a half months after the beginning of the eruption.2009-03-14T15:00:00Z宮城, 洋介On July 12 (UTC), 2008, Okmok volcano in the Aleutian Islands began to erupt after a lapse of 11 years. Okmok volcano is located on Umnak Island in the Aleutian volcanic chain, and has erupted from an active vent located in the southwest part of the caldera floor more than 10 times since 19th century. Although there are few habitants around Okmok volcano, ash from the eruption could lead to catastrophic airplane accidents because of the heavy air traffic over the Aleutian Islands. In the 2008 event, ash plumes were emitted up to 15,000m above sea level from the new vent located close to the caldera center, not the active vent. JAXA carried out several observations using ALOS/PALSR before and after the eruption. PALSAR can observe the volcano surface even if it is emitting a great deal of smoke. Comparing images acquired before and after the eruption, we detected surface changes on and around the Okmok caldera and could locate new vents in the area close to the caldera center. Using DInSAR technique of PALSAR data acquired after the eruption, we detected a deflation of the volcanic edifice for the period at least one and a half months after the beginning of the eruption.1988年雌阿寒岳の噴火活動に伴う地震活動の特性
http://hdl.handle.net/2115/38163
Title: 1988年雌阿寒岳の噴火活動に伴う地震活動の特性
Authors: 高木, 朗充
Abstract: Meakandake volcano is located southwest on the Akan caldera rim, the eastern part of Hokkaido. Four small eruptions occurred at Meakandake from January to February, 1988. Seismic activity was higher for one year including this eruption stage. Research Center for Earthquake Prediction of Hokkaido University (RCEP) installed temporal seismic array on the northwest flank of the volcanic edifice twenty days before the first eruption in order to clarify characteristics of seismicity associated with volcanic activity. Daily number of earthquakes became suddenly decreased, three days before the first eruption. And hypocenters were estimated to be very shallow by seismic amplitude ratios. After March 1988, deep low frequency events occurred frequently. During the observation, so various types of waveforms were recorded that we classified seismograms broadly in two groups. One is "simple event" and the other is "complex event". Mechanism of "complex event" is not so simpler than that of "simple event". "Simple event" is subclassified into three; HF, LF and PT. "Complex event" is subclassified into four; TD, TS, LD, and T. Dominant frequency of waveforms of "simple event" splits to 6 - 8 Hz and 10 - 13Hz, which correspond to LF and HF, respectively. There were four seismic swarms after eruptions. Waveforms in every swarm were so similar one another. Although they were, namely, earthquake family, they were able to be classified to LF and HF. And their first motions of seismograms were the same direction. In order to explain these characteristics, we proposed the tensile crack model with Doppler effect.2009-03-14T15:00:00Z高木, 朗充Meakandake volcano is located southwest on the Akan caldera rim, the eastern part of Hokkaido. Four small eruptions occurred at Meakandake from January to February, 1988. Seismic activity was higher for one year including this eruption stage. Research Center for Earthquake Prediction of Hokkaido University (RCEP) installed temporal seismic array on the northwest flank of the volcanic edifice twenty days before the first eruption in order to clarify characteristics of seismicity associated with volcanic activity. Daily number of earthquakes became suddenly decreased, three days before the first eruption. And hypocenters were estimated to be very shallow by seismic amplitude ratios. After March 1988, deep low frequency events occurred frequently. During the observation, so various types of waveforms were recorded that we classified seismograms broadly in two groups. One is "simple event" and the other is "complex event". Mechanism of "complex event" is not so simpler than that of "simple event". "Simple event" is subclassified into three; HF, LF and PT. "Complex event" is subclassified into four; TD, TS, LD, and T. Dominant frequency of waveforms of "simple event" splits to 6 - 8 Hz and 10 - 13Hz, which correspond to LF and HF, respectively. There were four seismic swarms after eruptions. Waveforms in every swarm were so similar one another. Although they were, namely, earthquake family, they were able to be classified to LF and HF. And their first motions of seismograms were the same direction. In order to explain these characteristics, we proposed the tensile crack model with Doppler effect.ボアホール地震観測網により観測された札幌周辺の微小地震
http://hdl.handle.net/2115/38162
Title: ボアホール地震観測網により観測された札幌周辺の微小地震
Authors: 吉田, 邦一; 笠原, 稔; 笹谷, 努
Abstract: On May, 1997, Sapporo municipality installed three borehole seismometers in Sapporo city to observe microearthquakes in and in its vicinity of Sapporo. Ueyama company has also installed strong-motion and high-gain seismometers at three borehole stations in and around Sapporo since 1999. We have collected seismic record from these borehole stations as well as other highgain seismic stations operated by various organizations and have determined hypocenters of 128 microearthquakes (M=0.2-2.8) occurring beneath Sapporo urban area from May, 1997 to January, 2004. Hypocentral distribution shows clusters of earthquakes near the central part and the eastern--southeastern part of Sapporo. A focal mechanism for one earthquake estimated from P-wave first motion polarities has nearly east--west pressure axis.2009-03-14T15:00:00Z吉田, 邦一笠原, 稔笹谷, 努On May, 1997, Sapporo municipality installed three borehole seismometers in Sapporo city to observe microearthquakes in and in its vicinity of Sapporo. Ueyama company has also installed strong-motion and high-gain seismometers at three borehole stations in and around Sapporo since 1999. We have collected seismic record from these borehole stations as well as other highgain seismic stations operated by various organizations and have determined hypocenters of 128 microearthquakes (M=0.2-2.8) occurring beneath Sapporo urban area from May, 1997 to January, 2004. Hypocentral distribution shows clusters of earthquakes near the central part and the eastern--southeastern part of Sapporo. A focal mechanism for one earthquake estimated from P-wave first motion polarities has nearly east--west pressure axis.高密度臨時地震観測による2004年斜里岳群発地震活動
http://hdl.handle.net/2115/38161
Title: 高密度臨時地震観測による2004年斜里岳群発地震活動
Authors: 一柳, 昌義; 高橋, 浩晃; 山口, 照寛; 高田, 真秀; 岡山, 宗夫; 笠原, 稔; 岡崎, 紀俊
Abstract: From April 27, 2004, Mt. Syari-dake earthquake swarm occurred in the eastern part of Hokkaido, Japan. The activity began at 4:19 on April 27, 2004. We installed nine temporary seismic stations around the seismic active area immediately after its occurrence and had continued the observation for about seven months. We determined 2228 hypocenters of earthquakes. It is found that the seismic active area is clearly distributed on the plane having southwest-northeast strike with dip angle of about 80 degrees. This plane well agrees with one of the nodal planes of the focal mechanisms of several earthquakes determined by P-wave first motions. Hypocenters migrate northeastward at a rate of 96 m/day and westward at a rate of 51 m/day. We also investigated hypocenter distribution before the installing of the temporary seismic stations. To improve accuracy of hypocenter determination we applied travel time correction for every permanent seismic stations. Relocated precise hypocenters demonstrate that the main seismic activity started to expand eastward just after the begining of the swarm.2009-03-14T15:00:00Z一柳, 昌義高橋, 浩晃山口, 照寛高田, 真秀岡山, 宗夫笠原, 稔岡崎, 紀俊From April 27, 2004, Mt. Syari-dake earthquake swarm occurred in the eastern part of Hokkaido, Japan. The activity began at 4:19 on April 27, 2004. We installed nine temporary seismic stations around the seismic active area immediately after its occurrence and had continued the observation for about seven months. We determined 2228 hypocenters of earthquakes. It is found that the seismic active area is clearly distributed on the plane having southwest-northeast strike with dip angle of about 80 degrees. This plane well agrees with one of the nodal planes of the focal mechanisms of several earthquakes determined by P-wave first motions. Hypocenters migrate northeastward at a rate of 96 m/day and westward at a rate of 51 m/day. We also investigated hypocenter distribution before the installing of the temporary seismic stations. To improve accuracy of hypocenter determination we applied travel time correction for every permanent seismic stations. Relocated precise hypocenters demonstrate that the main seismic activity started to expand eastward just after the begining of the swarm.