15 research outputs found
Estimation of SH-Wave Amplification in the Bandung Basin Using Haskell\u27s Method
The Bandung basin is a large basin in Indonesia surrounded by mountains that are associated with faults. There is the possibility of earthquakes generated by these faults shaking populated areas in the basin. The consequences will be worse because the shaking is amplified by the sediment layer of the basin. We have estimated the amplification of SH-waves generated by the Lembang fault using Haskell\u27s method for multilayer models. The pattern of amplification is a decreasing value with increasing distance from the Lembang fault. This pattern is valid for low-frequency incident waves. For higher-frequency incident waves, the pattern looks more complicated. Fortunately, there are many areas with low amplification values. Hopefully, this result will help the local government in making decisions regarding construction planning in this region. Of course, the final objective is to reduce earthquake risks
Estimation of SH-Wave Amplification in the Bandung Basin Using Haskellâs Method
The Bandung basin is a large basin in Indonesia surrounded by mountains that are associated with faults. There is the possibility of earthquakes generated by these faults shaking populated areas in the basin. The consequences will be worse because the shaking is amplified by the sediment layer of the basin. We have estimated the amplification of SH-waves generated by the Lembang fault using Haskell's method for multilayer models. The pattern of amplification is a decreasing value with increasing distance from the Lembang fault. This pattern is valid for low-frequency incident waves. For higher-frequency incident waves, the pattern looks more complicated. Fortunately, there are many areas with low amplification values. Hopefully, this result will help the local government in making decisions regarding construction planning in this region. Of course, the final objective is to reduce earthquake risks
Development of an Inversion Method for Low Velocity Medium
The main problem with the inversion of a low velocity medium is the application of an appropriate ray tracing method after choosing a suitable model parameterization. Block parameterization is not suitable, because it is not capable of representing the velocity model well. A large amount of blocks with a small grid size are needed to express the model well, but in that case, a ray coverage problem will be encountered. A knot-point parameterization model is better suited than a block model, because it can express the velocity model well, while the number of variables is much smaller. Ray calculation using the pseudo-bending method is not appropriate for the velocity model because of an instability problem at high velocity gradients. The crucial problem of this method involves the initial ray-path that is optimized in order to obtain the "true" ray, but does not satisfy the Fermat principle. These problems can be solved by applying the eikonal-solver method, because this can handle high-velocity gradients and does not need an initial ray path. Using a suitable model parameterization and appropriate ray tracing method, the inversion can obtain good results that fit the desired output. Applying a block model and the pseudo-bending method will not produce the desired output
Source Processes of the March 2007 Singkarak Earthquakes Inferred from Teleseismic Data
The rupture processes of two sequentialearthquakes have been inverted from teleseismic data. The first event released a total seismic moment of 7.9Ăâ1018 Nm (Mw 6.5) and the slip distribution shows three asperities, 1.5 m at the shallowside, 0.7 m at the rightsouth-east deep side and 0.5 m atthe north-west deep side. The second event had one asperity with 1.7 m slip and released a seismic moment of 7.5Ăâ1018 Nm (Mw 6.5). In both cases, maximum slip occurred above the hypocenter which was responsible for the surface displacement pattern
Estimation of S-wave Velocity Structures by Using Microtremor Array Measurements for Subsurface Modeling in Jakarta
Jakarta is located on a thick sedimentary layer that potentially has a very high seismic wave amplification. However, the available information concerning the subsurface model and bedrock depth is insufficient for a seismic hazard analysis. In this study, a microtremor array method was applied to estimate the geometry and S-wave velocity of the sedimentary layer. The spatial autocorrelation (SPAC) method was applied to estimate the dispersion curve, while the S-wave velocity was estimated using a genetic algorithm approach. The analysis of the 1D and 2D S-wave velocity profiles shows that along a north-south line, the sedimentary layer is thicker towards the north. It has a positive correlation with a geological cross section derived from a borehole down to a depth of about 300 m. The SPT data from the BMKG site were used to verify the 1D S-wave velocity profile. They show a good agreement. The microtremor analysis reached the engineering bedrock in a range from 359 to 608 m as depicted by a cross section in the north-south direction. The site class was also estimated at each site, based on the average S-wave velocity until 30 m depth. The sites UI to ISTN belong to class D (medium soil), while BMKG and ANCL belong to class E (soft soil)
Estimation of SH-Wave Amplification in the Bandung Basin Using Haskellâs Method
The Bandung basin is a large basin in Indonesia surrounded by mountains that are associated with faults. There is the possibility of earthquakes generated by these faults shaking populated areas in the basin. The consequences will be worse because the shaking is amplified by the sediment layer of the basin. We have estimated the amplification of SH-waves generated by the Lembang fault using Haskell's method for multilayer models. The pattern of amplification is a decreasing value with increasing distance from the Lembang fault. This pattern is valid for low-frequency incident waves. For higher-frequency incident waves, the pattern looks more complicated. Fortunately, there are many areas with low amplification values. Hopefully, this result will help the local government in making decisions regarding construction planning in this region. Of course, the final objective is to reduce earthquake risks
Characteristics of Earthquake-Generated Tsunamis in Indonesia Based on Source Parameter Analysis
We have characterized 27 earthquake-generated tsunamis from 1991 to 2012 in Indonesia, based on source parameter analysis. This includes the focal mechanism derived by W phase inversion analysis, the ratio (ĂË) between the seismic energy (E) and the seismic moment (Mo), the moment magnitude (Mw), the rupture duration (To) and the distance of the hypocenter to the trench. Most of the earthquakes (24 events) were tsunamigenic earthquakes with various fault types, a shallow focal depth (12 km ââ°Â¤ D ââ°Â¤ 77.8 km), a small to large magnitude (6.6 ââ°Â¤ Mw ââ°Â¤ 9.0), a low ratio of seismic energy to seismic moment (-5.8 < ĂË < -4.9), a short to long rupture duration (27 s ââ°Â¤ To ââ°Â¤ 257 s), a small to large tsunami height (0.1 m ââ°Â¤ H ââ°Â¤ 50.9 m) and a short to long distance from the hypocenter to the trench (10 km < HT ââ°Â¤ 230 km). Three tsunami earthquakes were characterized by a thrust fault mechanism, a very shallow depth (D ââ°Â¤ 20 km), a moderate magnitude (7.5 ââ°Â¤ Mw ââ°Â¤ 7.8), a very low ratio of seismic energy to seismic moment (ĂË Ă˘â°Â¤ -5.8), a long rupture duration (99 s ââ°Â¤ To ââ°Â¤ 135 s), a large tsunami height (7.4 m ââ°Â¤ H ââ°Â¤ 14 m) and a short distance from the hypocenter to the trench (HT ââ°Â¤ 20 km)
Characteristics of Earthquake-Generated Tsunamis in Indonesia Based on Source Parameter Analysis
We have characterized 27 earthquake-generated tsunamis from 1991 to 2012 in Indonesia, based on source parameter analysis. This includes the focal mechanism derived by W phase inversion analysis, the ratio (ĂË) between the seismic energy (E) and the seismic moment (Mo), the moment magnitude (Mw), the rupture duration (To) and the distance of the hypocenter to the trench. Most of the earthquakes (24 events) were tsunamigenic earthquakes with various fault types, a shallow focal depth (12 km ââ°Â¤ D ââ°Â¤ 77.8 km), a small to large magnitude (6.6 ââ°Â¤ Mw ââ°Â¤ 9.0), a low ratio of seismic energy to seismic moment (-5.8 < ĂË < -4.9), a short to long rupture duration (27 s ââ°Â¤ To ââ°Â¤ 257 s), a small to large tsunami height (0.1 m ââ°Â¤ H ââ°Â¤ 50.9 m) and a short to long distance from the hypocenter to the trench (10 km < HT ââ°Â¤ 230 km). Three tsunami earthquakes were characterized by a thrust fault mechanism, a very shallow depth (D ââ°Â¤ 20 km), a moderate magnitude (7.5 ââ°Â¤ Mw ââ°Â¤ 7.8), a very low ratio of seismic energy to seismic moment (ĂË Ă˘â°Â¤ -5.8), a long rupture duration (99 s ââ°Â¤ To ââ°Â¤ 135 s), a large tsunami height (7.4 m ââ°Â¤ H ââ°Â¤ 14 m) and a short distance from the hypocenter to the trench (HT ââ°Â¤ 20 km)
Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa-Shizuoka Earthquake
International audienceThe Itoigawa-Shizuoka Tectonic Line (ISTL) is a major oblique left-lateral crustal fault that is expected to host M7+ events in the near future. Its proximity to the Kanto sedimentary basin poses a threat to the population of Metropolitan Tokyo. This study constructs ground motion predictions for scenario earthquakes on the ISTL using virtual earthquakes. We use the ambient seismic field to calculate the cross-correlation function that we assume proportional to the elastodynamic Green tensor between High-Sensitivity Seismograph network stations, which act as sources located above the ISTL, and the stations of the dense Metropolitan Seismic Observation network, which act as receivers in the Kanto Basin. We use the virtual earthquake approach (Denolle et al., 2013, https://doi.org/10.1029/2012JB009603; Denolle, Dunham, et al., 2014, https://doi.org/10.1126/science.1245678) to predict ground motion from a suite of 270 kinematic sources and find that predicted ground motions are strong enough that nonlinear effects, which we do not model, may become important. We find that the shape of the sedimentary basin substantially alters the shaking by amplifying long-period ground motions as seismic waves refract at the basin edge. Additionally, we quantify ground motion variability due to source uncertainty, surmise that ground motions are lognormally distributed with regard to source uncertainties, and suggest that the variability is affected (locally either enhanced or reduced) by the basin shape. Finally, we find a coupling point between source and wave paths for epicentral locations on the ISTL that generates almost twice the shaking as equivalent unilateral ruptures, despite directivity orientation that would favor southward ruptures