| PaperNO | Paper / Abstract |
|
D3-012
13:30
|
13:45
|
JOINT MODELING OF RECEIVER FUNCTION AND HORIZONTAL-TO-VERTICAL SPECTRAL RATIO FOR SHALLOW SHEAR-WAVE VELOCITY STRUCTURE
The shallow structure dominates the site amplification and waveform duration of strong ground motion and increases the seismic hazard. In Taiwan, the depth of the shallow part we care is between hundreds of meters and two kilometers to include the soft sediments and the basement. After the 1999 Chi-Chi Earthquake, several methods have been applied to study the shallow velocity structure in Taiwan. One of them is the Receiver Function (RF) of strong-motion records which has been proved that this method is effective to estimate shallow subsurface structures, especially for bedrocks and basin structures, in our previous study. The shallow shear velocity profiles of over 700 strong-motion stations were estimated by modeling of receiver functions. Moreover, a dense microtremor survey has been conducted in Taiwan to study the site characteristics using the Horizontal-to-vertical Spectral Ratio (HVSR) method. Also, the shallow velocity structures controlling the site effect were estimated by HVSR inversions. After these studies, the theoretical transfer functions of RF velocity structures for all stations are calculated and compared with their empirical HVSRs of historical records to evaluate the site amplification of our results. However, some stations show notable differences between the theoretical and empirical transfer functions. Therefore, we design an approach to model RF and HVSR jointly for estimating shallow velocity profiles beneath strong-motion stations. Because RFs are primarily sensitive to velocity contrasts based on the time-domain converted phases, and HVSRs are also sensitive to velocity contrasts but based on the frequency-domain site amplification. The joint modeling of their combination provides the reliable estimation of velocity structures which conforms to the real site effect in time-domain and frequency-domain at the same time. The velocity contrasts, generating the converted phases and controlling the site amplification, can be reconstructed in the estimated velocity structure. The differences between the results estimated from the RF, HVSR, and joint methods are also compared and discussed in this study.
Che-Min Lin, Chun-Hsiang Kuo, Chun-Te Chen, Jyun-Yan Huang, Kuo-Liang Wen
H/V spectral ratio, Microtremor, Receiver function, Shear-wave velocity model, Site response
|
|
D3-013
13:45
|
14:00
|
SHALLOW SHEAR WAVE VELOCITY STRUCTURE IN TAIWAN INFERRED FROM MICROTREMOR ANALYSIS
The high-resolution shallow velocity structure could provide site parameters like Vs30 or Z1.0 for engineering propose and it is an essential component for improving the ground motion prediction. To this end, we investigate and create the shallow velocity structures in Taiwan derived from the dense microtremor survey. Based on diffuse field theory one station microtremor measurement can be used for inversion of the microtremor Horizontal-to-vertical spectra ratio (MHVSR) to obtain the 1D velocity profile. The computer code HV-Inv is applied for calculation of the MHVSR and inversion of the Vs profiles for diffuse wave fields in Taiwan. The resolution in the spatial can up to 1km in urban areas like Taipei, Kaohsiung city and Ilan plain, the other area is about 2km. The velocity profiles obtain by the microtremor array are design to a suitable initial search range for each site to mitigate non-uniqueness. The velocity profiles of this study and well logging data have a good agreement. The results can use to update a detail Vs30 map in Taiwan, the depth contour of engineer bedrock and Z1.0 also can be mapped. Moreover, the relations of Vs30–Z1.0 was also developed. The shallow structures can be applied to strong motion predictions or numerical simulations, which can also be helpful for earthquake disaster prevention work.
Che-Min Lin, Chun-Hsiang Kuo, Jyun-Yan Huang, Chun-Te Chen, Kuo-Liang Wen
diffuse field theory, HVSR, Microtremor, shallow velocity, Vs30, Z1.0
|
|
D3-014
14:00
|
14:15
|
BUILDING 3-D SHALLOW S-WAVE VELOCITY MODEL BY SPATIAL INTERPOLATION IN THE TAIPEI BASIN
Chi-Chi earthquake occurred on 21, September 1999 is the most important earthquake event in modern Taiwan. More than 2000 people died and billions of economic damage caused in this event.Due to the thick and soft sediment beneath the Taipei basin, the basin effect made wave amplify and duration extend. This is one of the key reasons why the epicenter of the Chi-Chi earthquake was located on Nantou County in central Taiwan, but the impact to Taipei basin was still huge. In order to reduce earthquake disaster, many academic centers and government agencies started to explore the geological structure under the Taipei basin in decades. Hence, the purposes of this study is to model the three dimentional S-wave velocity structure by the ordinary kriging. The data obtained by the suspension P-S logging, the microtremor array, the horizontal-to-vertical spectral ratio (H/V) and the receiver function approaches were used. Moreover, according to the spatial distribution of these data, three depth scales were divided and two type of the semivariogram scenario were tested. The result showed that the ordinary kriging only consider horizontal smivariogram obtained the less error by cross-validation.
Xue-Min Lu, Che-Min Lin, Chun-Hsiang Kuo, Jyun-Yan Huang
ordinary kriging, S-wave velocity, Taipei basin
|
|
D3-011
14:15
|
14:30
|
SHALLOW CRUSTAL VELOCITY STRUCTURES BENEATH WESTERN FOOTHILLS OF TAIWAN REVEALED BY AMBIENT SEISMIC NOISE
The Western Foothills geologic province is located along the deformation front of the Taiwan Orogen. This area includes highly active faults and a complex seismogenic structure that have historically caused serious damage. A temporary seismic network with around 40 broadband seismometers had been set up to monitor the seismicity surrounding the three Science Parks between Hsinchu and Tainan County by the National Center for Research on Earthquake Engineering (NCREE) between 2006 and 2010. Previous studies were rather focused on locating seismic events and travel time tomography to understand the tectonic and velocity structures. Meanwhile, the characteristics of ground motion and fault activity could be further studied.The time domain empirical Green’s function (TDEGFs) can be obtained from the cross-correlation of station pairs with simultaneous and continuous ambient seismic noise signals. This method uses diffuse wave fields with passive structural signals contained in ambient seismic noise. Since the basic theorem of ambient seismic noise has been verified, the investigations of subsurface velocity structures have provided important constrains in various parts of the world with routine data processing over the past decade. Data quality of daily vertical components was preliminarily assessed to calculate the cross-correlation function (CCF) with a 200-s lag time for each station pair in the 1–15-s period band. The daily CCFs were stacked monthly and the monthly CCFs were then stacked to retain coherent signals for acquiring TDEGFs and Rayleigh-wave phase-velocity dispersion curves. Tomography was applied to preliminarily construct 1–10-s Rayleigh-wave phase-velocity maps with 0.1° grid spacing and lateral velocity variations showed dramatic patterns among different geologic provinces. Shallow crustal S-wave velocity (Vs) structures will be further obtained and the results will try to be demonstrated with two-dimensional and three-dimensional models. The obtained shallow crustal velocity structures of this research could help to construct strong ground motion, which are particularly important for mitigating seismic hazards of the densely populated metropolitan area in western Taiwan.
Yu-Chih Huang, Hung-Hao Hsieh, Chau-Huei Chen, Che-Min Lin, Kuo-Liang Wen
ambient seismic noise, crustal velocity structures, Western Foothills of Taiwan
|
|
E0-011
14:30
|
14:45
|
SCALING RELATIONSHIP OF THE PULSE-LIKE VELOCITY GROUND MOTIONS OF THE DISASTROUS EARTHQUAKES
The pulse-like velocity ground motions which observed firstly in 1994 Northridge and 1995 Kobe earthquake had shown to give significant impact to earthquake hazards. The moderate earthquakes in Taiwan, M W 6.6 Meinong in 2016 and M W 6.4 Hualien earthquake in 2018, also observed the pulse-like velocity ground motions that brought serious damage to nearby buildings. Some seismological engineers and seismologists advocated that the pulse-like velocity ground motions were caused by the rupture directivity effect from the epicenter. In this study, we analyzed the seismic records from the stations of Taiwan Strong Motion Implementation Program (TSMIP) and recognized the pulse-like velocity ground motions were more associated with near-by asperity in the rupture direction. Here we define the area with slips larger than 1.5 of the average slip as the area of asperity on fault plane. We examined the stations with pulse-like velocity motions to the distance of the asperity to reveal the possible scaling relationship. The amplitudes of these velocity pulses close to the asperity were higher than those of stations with similar distance to the fault. A rupture directivity effect from the associated asperity was observed rather than from epicenter. The observed period of the pulse-like velocity motion varied from 2-5 sec. We further analyze the seismic records to understand the possible association of the periods of the velocity pulses to the dimension of the asperity or the basin effect, and hopefully to understand the control factors of these period of the velocity pulses. Our preliminary observations show that the pulse-like velocity ground motions are caused by the strong directivity effect from the largest asperity and the periods of the pulse-like velocity ground motions are associated with the area of the largest asperity. In addition, we further perform the simulations by simple FK method to clarify the causes and the scaling relationship of the periods of the velocity pulses observed from the records. Through using the observation and simulation, we aim to reveal the scaling relationship of the period of the velocity pulses and the asperity and the importance of the velocity pulses bringing the damage to buildings in moderate earthquake hazards. The complete understanding the effects of the velocity pulses from the seismic source to sites is important for seismic hazard assessment of moderate earthquakes like this kind.
Kuo-Fong Ma, Ya-Ting Lee, Yen-Yu Lin, Ming-Hsuan Yen
directivity effects, pulse-like velocity ground motions, scaling relationship
|
|
E1-011
14:45
|
15:00
|
Near-field velocity pulse-like ground motions on February 6, 2018 MW6.4 Hualien, Taiwan Earthquake and structure damage implications
The February 6, 2018 Hualien Taiwan Earthquake (Mw6.4) had caused serious fatalities and severe building damages in Hualien city. Substantial near-field velocity pulse-like ground motions were probably one of the important factors. We used the continuous wavelet transforms method to identify the velocity pulse-like ground motions from orthogonal components of all the recorded ground motions. The identification results were in agreement with the contour map of pulse-like occurrence probability according to two prediction models for non strike-slip faults. 16 near-field recordings were recognized as the pulse-like ones, and the pulse period (Tp) was then determined individually. The multiple degrees of freedom (MDOF) systems were implemented in the computation of inelastic demand and story ductility demand. The results indicated that the maximum ductility demand exists at the bottom story of the 7-story，9-story and 11-story MDOF structure subject to the pulse-like records. For the case of reduced shear strength and stiffness at the bottom story due to removed infill walls, the bottom ductility demand reach more than 10.0 under pulse-like records. These findings support the supposition that large ductility demand and the bottom soft-story mechanism under near-field velocity pulse-like ground motions were the main reasons for severe structural damage of the four near-field mid-rise RC buildings during the Hualien earthquake.
Ji Kun, Ren Yefei, Wen Ruizhi, Kuo Chun-Hsiang
ductility demand;, Hualien earthquake, pulse period, velocity pulse-like records
|