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C1-011
14:20
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14:35
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DYNAMIC MODELING ON STRESS MODEL OF THE 1999 CHI-CHI, TAIWAN, EARTHQUAKE
We carried out dynamic modeling (3DEC) of the 1999 Chi-Chi, Taiwan, earthquake with stress model to understand implication of the in-situ stress result of the Taiwan Chelungpu-fault Drilling Project (TCDP) at depth of disturbance fault zone. Stress model is constrained by the studies of TCDP. We tested direction of maximum and minimum horizontal stress according to observation of stress rotations in the vicinity of the shallowest major fault zone. Additional stress on maximum horizontal stress was considered to recover the stress release from the Chi-Chi earthquake. Time?weakening constitutive law was deployed to simulate unspontaneous dynamic rupture, while the stress drop was used as input, from kinematic modeling of waveform inversion. After testing, we obtained a model, which shows small residual on the displacement between GPS records and synthetic results. Comparison of strong motion velocity and displacement records and synthetic seismograms generated by numerical modelling are also acceptable and reasonable. We, thus, suggest the dynamic modelling to understand the stress model before the Chi-Chi earthquake might be applicable through this exercise.
Yuan-Chieh Wu, Chi-Jen Chen, Kuo-Fong Ma
1999 Chi-Chi Earthquake, 3DEC, dynamic modelling, in-situ stress
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C1-013
14:35
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14:50
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SOURCE PARAMETER STUDY AND GROUND MOTION SIMULATION OF 1604 QUANZHOU EARTHQUAKE
The 1604 Quanzhou earthquake (M7.5-8.0) was the largest earthquake in the Taiwan Strait in history. According to the historical literatures, this earthquake caused several deaths and severe damage in the inland China along the southeast coast. Tectonically, Taiwan Strait is a relative stable tectonic environment compared to Taiwan island as the plate boundary of significant tectonic activity. The understanding of its corresponding impact of the ground motions in Taiwan and surrounding islands resulted from the 1604 Quanzhou earthquake are important. In this study, we investigated the historical 1604 Quanzhou earthquake through modern technique in waveform modeling through forward waveform simulation using earthquake scaling in asperity, stress drop, and source time function and hybrid methods. The various possibilities of the source parameter models from three previous determined focal mechanisms following scaling law and hybrid technique were constructed to examine the possible slip distribution on the fault and the associated magnitude. We compare the simulation results to the ground shaking intensities from the historical literatures and provide the synthetic waveforms at the pseudo subsurface sites. To achieve these goals, the subsurface structure and the velocity model in the Taiwan Strait were also constructed, and the techniques and processes for simulation was established to obtain the source parameters for further understanding of the ground shaking in several locations within Taiwan Strait. As the results from hybrid simulation using the “recipe”, the intensity pattern from the model with an oblique right-lateral mechanism with asperity has the most similar to the historical intensities of the 1604 Quanzhou earthquake. Through the results from different stress drop in simulations, our studies suggested that this 1604 earthquake might have high stress drop as the values of about 100 bars.
Yiwun Liao, Ming Hsuan Yen, Kou-Fong Ma
1604 Quanzhou earthquake, Source parameter, Taiwan Strait, Velocity Structure
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C1-014
14:50
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15:05
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Simulation of PGV of 1920 Hualien earthquake with 3DEC: comparison with historical seismic intensity
Since it’s not easy to get data like shear displacement of fault plane below surface or earthquake in the past, simulation technic has been used in various ways to help scientists reveal the phenomenon of earthquake. Also, simulation technic helps scientists and engineering groups evaluate the effects and disasters that might be induced by earthquakes in the future. For scientific purposes and long-term performance assessment requirements, we build models for assessing possible PGV and its relationships with source parameters like location of asperity and average stress drop. We choose 3DEC software, which has been used and confirmed as a useful tool for rock mechanics modeling, as our base and create a fault source model that can be used in earthquake dynamic modeling. The advantage of this model is that we can control the magnitude of earthquake with stress drop and stress environments easily, so do the numbers, locations and areas of asperities. In order to understand the confidence of our model, we create different fault geometry models with various fault dips, fault length, fault width and fault depth according to published studies of the 1920 Hualien earthquake. Each fault geometry model will be tested with 6 different locations of asperities, and the corresponding stress drop is applied to find the best fit with historical seismic intensity record. Our results suggest that the PGV and surface deformation is significantly controlled by the location of asperity. However, more efforts are still needed to improve the reliability and capability of this model.
Yuan-Chieh Wu, Chi-Jen Chen, Chih-Cheng Chung
1920 Hualien Earthquake, earthquake simulation, PGV
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C1-015
15:05
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15:20
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Rupture Dynamics of the 2012 Nicoya Mw 7.6 Earthquake and its Application in Physics-based Ground Velocity Predictions
Frictional properties on faults play a critical role in controlling rupture generation and propagation, thus significantly impact ground shaking intensities and tsunami potential during megathrust earthquakes. However, estimation of in-situ frictional properties remains challenging, mainly hampered by inadequate near-field observations and intrinsic trade-offs between parameters. Here, we determine frictional properties on the megathrust ruptured in the 2012 Nicoya Mw 7.6 earthquake by conducting 3D dynamic simulations with constraints from kinematic source models and records on local GPS network installed on the Nicoya Peninsula. Through dynamic rupture simulations with a wide range of frictional parameters, we compare the final slip distribution with kinematic models and our synthetic ground velocities with near-field observations. Our best-fit model indicates a low fracture energy ~0.45MJ/m^2, with the critical weakening distance ~0.25m and the strength drop ~ 3.6MPa. We further investigate the parameter range in our dynamic simulations by only focusing on the peak ground velocities (PGV), which are critical in seismic hazard assessment. The comparison between model results and high-rate GPS data in PGV determines a suitable range for frictional properties that can be applied in future physics-based ground velocity predictions.
Suli Yao, Hongfeng Yang
frictional properties, physics-based PGV prediction, rupture dynamics, the 2012 Nicoya Mw 7.6 earthquake
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C1-016
15:20
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15:35
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INFLUENCE OF LOW-VELOCITY LAYERS IN THE PHILIPPINE SEA PLATE REGION ON LONG-PERIOD GROUND MOTION IN THE TOKYO METROPOLITAN AREA
Long-period (2–4 s) ground motion was observed in the Tokyo metropolitan area during the mainshock of the 2011 Great East Japan Earthquake seismic sequence, which caused severe damage to super high-rise buildings: large interstory deformation and the moving and/or overturning of furniture. The prediction of long-period ground motion in the Tokyo region has become an important subject, because there are two subduction zones offshore of the eastern Tokyo region: The Suruga and the Sagami troughs. The existence of a low-velocity layer along the Suruga Trough increases the risk of a future Tokai Earthquake, with a focal region in the Suruga Trough. Because of the existence of a low-velocity layer along the Suruga Trough, the risk of the assumed Tokai earthquake with the focal region in Suruga Trough is highly concerned. It is therefore important to clarify the influence of these low-velocity strata on the generation of long-period ground motion in the Tokyo region. Here, the three-dimensional (3D) finite difference method (FDM) was used for wave propagation analysis to investigate the influence of low-velocity layers on long-period ground motion by embedding a low-velocity layer (VS = 1 km/s) in seismic bedrock (VS = 3 km/s). Furthermore, theoretical simulations of the seismic motions were performed based on the reciprocity relations using the 3D-FDM model to investigate different source locations. The source and observation points can be exchanged via the reciprocity relations, such that the designated stations (e.g., K-NET Shinjuku station) can be regarded as sources and the point sources at the plate boundary (e.g., Suruga Trough) can be treated as receivers. It is found that the maximum velocity of the seismic motion in the Tokyo metropolitan area can be suppressed by the existence of low-velocity layers.
Xin Wang, Masayuki Nagano, Tomohiro Oguchi
Finite difference method, Interplate earthquakes, Long-period ground motion, Low-velocity layers, Reciprocity relations, Tokyo metropolitan area
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C3-015
15:35
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15:50
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TECTONIC IMPLICATIONS OF SOIL-GAS MONITORING FOR EARTHQUAKE SURVEILLANCE IN TAIWAN
The island of Taiwan is a product of the collision between the Philippine Sea plate and Eurasian plate which makes it a region of high seismicity. Active subduction zones occur south and east of Taiwan. After the destructive Chi-chi earthquake (MW = 7.6, Sept. 21, 1999) an accelerated phase of geochemical monitoring started in Taiwan. Measurement of soil-gas emissions along active zones is characterized as a geochemical tool to identify and monitor tectonic activity in the region. Geochemical variations of soil-gas composition in the vicinity of geologic fault zone of Northeastern and Southwestern parts of Taiwan have been studied in detail recently. To carry out the investigation, temporal soil-gases variations are measured at continuous earthquake monitoring stations established along different faults. The present investigations aim at developing an effective earthquake precursory system from the long term soil-gas data obtained from a network of soil-gas monitoring stations covering NW, SW and eastern Taiwan. As per the present practice, the data from various stations are examined synoptically to evaluate earthquake precursory studies. The present study is also aimed at the appraisal and filtrations of these environmental/meteorological parameters and to create an automated real-time database for earthquake precursory study. During the observation period of 2015, about 34 earthquakes of magnitude ? 5 were recorded and out of these, 16 earthquakes fell under the defined selection criteria and were tested in the proposed model. From all the monitoring station data it has been found that Jaosi monitoring station has recorded the maximum number of earthquakes whereas Hsincheng monitoring station has highest efficiency. It has also been found that 3 earthquakes lie in the common influence area of all the monitoring stations. Out of these, 2 earthquakes happened to have precursory signals which can be correlated with the occurred earthquake whereas one earthquake has shown precursory signals at HC and HH monitoring stations.
Vivek Vivek Walia, Arvind Kumar, Ching-Chou Fu, Shih-Jung Lin, Cheng-Horng Lin
Earthquake, Precursors, Radon, Geochemical, Taiwan
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