Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakes
Abstract The Himalayan collision zone experiences many seismic activities with large earthquakes occurring at certain time intervals. The damming of the proto-Bagmati River as a result of rapid mountain-building processes created a lake in the Kathmandu Valley that eventually dried out, leaving thic...
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| Format: | Article |
| Language: | English |
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SpringerOpen
2017-07-01
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| Series: | Earth, Planets and Space |
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| Online Access: | http://link.springer.com/article/10.1186/s40623-017-0685-4 |
| _version_ | 1811322244979228672 |
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| author | Subeg M. Bijukchhen Nobuo Takai Michiko Shigefuji Masayoshi Ichiyanagi Tsutomu Sasatani Yokito Sugimura |
| author_facet | Subeg M. Bijukchhen Nobuo Takai Michiko Shigefuji Masayoshi Ichiyanagi Tsutomu Sasatani Yokito Sugimura |
| author_sort | Subeg M. Bijukchhen |
| collection | DOAJ |
| description | Abstract The Himalayan collision zone experiences many seismic activities with large earthquakes occurring at certain time intervals. The damming of the proto-Bagmati River as a result of rapid mountain-building processes created a lake in the Kathmandu Valley that eventually dried out, leaving thick unconsolidated lacustrine deposits. Previous studies have shown that the sediments are ~600 m thick in the center. A location in a seismically active region, and the possible amplification of seismic waves due to thick sediments, have made Kathmandu Valley seismically vulnerable. It has suffered devastation due to earthquakes several times in the past. The development of the Kathmandu Valley into the largest urban agglomerate in Nepal has exposed a large population to seismic hazards. This vulnerability was apparent during the Gorkha Earthquake (Mw7.8) on April 25, 2015, when the main shock and ensuing aftershocks claimed more than 1700 lives and nearly 13% of buildings inside the valley were completely damaged. Preparing safe and up-to-date building codes to reduce seismic risk requires a thorough study of ground motion amplification. Characterizing subsurface velocity structure is a step toward achieving that goal. We used the records from an array of strong-motion accelerometers installed by Hokkaido University and Tribhuvan University to construct 1-D velocity models of station sites by forward modeling of low-frequency S-waves. Filtered records (0.1–0.5 Hz) from one of the accelerometers installed at a rock site during a moderate-sized (mb4.9) earthquake on August 30, 2013, and three moderate-sized (Mw5.1, Mw5.1, and Mw5.5) aftershocks of the 2015 Gorkha Earthquake were used as input motion for modeling of low-frequency S-waves. We consulted available geological maps, cross-sections, and borehole data as the basis for initial models for the sediment sites. This study shows that the basin has an undulating topography and sediment sites have deposits of varying thicknesses, from 155 to 440 m. These models also show high velocity contrast at the bedrock depth which results in significant wave amplification. Graphical abstract . |
| first_indexed | 2024-04-13T13:32:57Z |
| format | Article |
| id | doaj.art-b54e4937019d481481a3d6cb6246926d |
| institution | Directory Open Access Journal |
| issn | 1880-5981 |
| language | English |
| last_indexed | 2024-04-13T13:32:57Z |
| publishDate | 2017-07-01 |
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| series | Earth, Planets and Space |
| spelling | doaj.art-b54e4937019d481481a3d6cb6246926d2022-12-22T02:44:55ZengSpringerOpenEarth, Planets and Space1880-59812017-07-0169111610.1186/s40623-017-0685-4Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakesSubeg M. Bijukchhen0Nobuo Takai1Michiko Shigefuji2Masayoshi Ichiyanagi3Tsutomu SasataniYokito Sugimura4Graduate School of Engineering, Hokkaido UniversityFaculty of Engineering, Hokkaido UniversityFaculty of Human-Environment Studies, Kyushu UniversityInstitute of Seismology and Volcanology, Hokkaido UniversityJapan Water AgencyAbstract The Himalayan collision zone experiences many seismic activities with large earthquakes occurring at certain time intervals. The damming of the proto-Bagmati River as a result of rapid mountain-building processes created a lake in the Kathmandu Valley that eventually dried out, leaving thick unconsolidated lacustrine deposits. Previous studies have shown that the sediments are ~600 m thick in the center. A location in a seismically active region, and the possible amplification of seismic waves due to thick sediments, have made Kathmandu Valley seismically vulnerable. It has suffered devastation due to earthquakes several times in the past. The development of the Kathmandu Valley into the largest urban agglomerate in Nepal has exposed a large population to seismic hazards. This vulnerability was apparent during the Gorkha Earthquake (Mw7.8) on April 25, 2015, when the main shock and ensuing aftershocks claimed more than 1700 lives and nearly 13% of buildings inside the valley were completely damaged. Preparing safe and up-to-date building codes to reduce seismic risk requires a thorough study of ground motion amplification. Characterizing subsurface velocity structure is a step toward achieving that goal. We used the records from an array of strong-motion accelerometers installed by Hokkaido University and Tribhuvan University to construct 1-D velocity models of station sites by forward modeling of low-frequency S-waves. Filtered records (0.1–0.5 Hz) from one of the accelerometers installed at a rock site during a moderate-sized (mb4.9) earthquake on August 30, 2013, and three moderate-sized (Mw5.1, Mw5.1, and Mw5.5) aftershocks of the 2015 Gorkha Earthquake were used as input motion for modeling of low-frequency S-waves. We consulted available geological maps, cross-sections, and borehole data as the basis for initial models for the sediment sites. This study shows that the basin has an undulating topography and sediment sites have deposits of varying thicknesses, from 155 to 440 m. These models also show high velocity contrast at the bedrock depth which results in significant wave amplification. Graphical abstract .http://link.springer.com/article/10.1186/s40623-017-0685-41-D simulationVelocity modelPropagator matrixDiffused field theoryKathmandu Valley |
| spellingShingle | Subeg M. Bijukchhen Nobuo Takai Michiko Shigefuji Masayoshi Ichiyanagi Tsutomu Sasatani Yokito Sugimura Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakes Earth, Planets and Space 1-D simulation Velocity model Propagator matrix Diffused field theory Kathmandu Valley |
| title | Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakes |
| title_full | Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakes |
| title_fullStr | Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakes |
| title_full_unstemmed | Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakes |
| title_short | Estimation of 1-D velocity models beneath strong-motion observation sites in the Kathmandu Valley using strong-motion records from moderate-sized earthquakes |
| title_sort | estimation of 1 d velocity models beneath strong motion observation sites in the kathmandu valley using strong motion records from moderate sized earthquakes |
| topic | 1-D simulation Velocity model Propagator matrix Diffused field theory Kathmandu Valley |
| url | http://link.springer.com/article/10.1186/s40623-017-0685-4 |
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