Ground-Motion Attenuation Relationships for Subduction- Zone Earthquakes in Northern Taiwan

Transcription

1 Ground-Motion Attenuation Relationships for Subduction- Zone Earthquakes in Northern Taiwan Lin, P.S., Lee, C.T. Bulletin of the Seismology Society of America (2008) Presenter: Yang Pei-Xin Adviser: Lee Chyi-Tyi Date: Dec. 14, 2017

2 01 Introduction and Motivation 目录 Outline CONTENTS Data Acquisition and Analysis Attenuation Model and Regression Method 04 Results 05 Discussion 06 Conclusions and Recommendations

3 01 Introduction and Motivation

4 01-1 Introduction and Motivation What is Ground Motion Attenuation Equations? They are used to estimate the ground-motion value for earthquakes. Magnitude Distance Site condition Ground Motion Attenuation Equations Ground Motion Value

5 01-2 Introduction and Motivation Response Spectrum Analysis The response spectrum is the maximum response of a single degree of freedom oscillator with a given damping value for a given period. To find an earthquake s response spectrum, we calculate the 5% critical-damping ratio response spectrum, with periods ranging from 0.01 to 5 sec, at sampling intervals of 0.01 sec. underdamping over damping (acceleration) (velocity) (displacement) maximum response value nature period critical-damping ratio = actual damping critical damping critical damping

6 01-3 Introduction and Motivation 1. To understand the ground-motion attenuation characteristics of subduction zone earthquakes that occur in northern Taiwan 2. To establish a set of appropriate attenuation equations for subduction zone earthquakes for probabilistic seismic hazard analysis(psha) studies peak ground attenuation (PGA) equations response spectral acceleration (SA) attenuation equations

7 01-4 Introduction Study Area

8 02 Data Acquisition and Analysis

9 02-1 Data Acquisition and Analysis 54 earthquakes : 17 interface, 37 intraslab subduction zone tectonic study mechanism classification choose study area earthquake catalog 1991/03~2000 strong motion data earthquake parameters calculate 5% criticaldamping ratio response spectrum attenuation model regression analysis site classification (rock sites ; soil sites) earthquake data : CWB (Central Weather Bureau) foreign ground-motion data for large magnitude subduction zone earthquake moment magnitude : HVD (Harvard Centroid Moment Tensor database) (Huang et al., 2000) BATS (Broadband Array in Taiwan for Seismology ) strong motion data : TSMIP (Taiwan strong-motion instrumentation program) SMART1 array (1983~1986) site classification : Lee et al. (2001)

10 02-2 Data Acquisition and Analysis attenuation model regression analysis PGA attenuation equations and SA attenuation equations interface earthquake intraslab earthquake rock soil rock soil

11 02-4 Subduction Zone Earthquake Classification Subduction zone earthquake Byrne et al.(1988) interface earthquake: shallow angle thrust event intraslab earthquake: mainly high- angle normal- faulting

12 02-4 Subduction Zone Earthquake Classification earthquakes (1991/03 ~ 2000 ) depth<=35km 35<depth<=50km depth>50km manual judgement not in the subduction zone no shallow angle thrust event mainly highangle normalfaulting yes yes no no yes shallow crustal earthquake interface earthquake other earthquake intraslab earthquake

13 02-4 Conversion Equation of ML and Mw

14 02-5 Strong Motion Data baseline correction After screening, there were 4,383 sets of data available Site Classification Site classification of TSMIP strong-motion stations proposed by Lee et al. was used, and sites were simplified as rock sites (B,C) or soil sites (D,E). Borcherdt(1994a,b)

15 03 Attenuation Model and Regression Method

16 03-1 Attenuation Model (Joyner and Boore, 1981) (3-1) y : ground-motion parameter B 1 : constant f 1 (M) : function relevant to the magnitude f 2 (R) : function related to distance ε random effect f 3 (M, R) : function related to magnitude and distance f 4 (Pi) : parameter related to site effects or the effect of structure or (3-1)

17 03-2 Regression Method PGA attenuation form i : ith earthquake j : jth station PGA ij : geometric mean of two horizontal PGA values M : moment magnitude R : hypocentral distance (km) H : focal depth (km) Z t : earthquake type (inter : Zt=0 ; intra : Zt=1) ln ε : random effect Response spectral attenuation form SA : amplitude of the response spectrum for each period

18 03-3 Least-squares Regression Method The least-squares basis for nonlinear regression model is are the mean responses for the ith earthquake and jth station following the nonlinear function. Block hill-climbing Search Method (Russel and Norvig, 2003) Hill-climbing Method

19 04 Results

20 04 Results and Evaluations : :

21 (a) rock site and (b) soil site for interface earthquake

22 (a) rock site and (b) soil site for intraslab earthquake

23 (a) rock site and (b) soil site for intraslab earthquake PGA attenuation The coefficient of depth term (H) is positive.

24 PGA and SA attenuation curves for intraslab earthquakes, rock site depth : 50 km

25 PGA and SA attenuation curves for intraslab earthquakes, soil site depth : 50 km

26 Histograms of lny residual fitted to a normal distribution curve example : SA equations for rock site

27 05 Discussion

28 05 Discussion

29 05 Discussion R=50 km Depth=50 km rock site soil site

30 05 Discussion Mw=6 Depth=50 km rock site soil site

31 06 Conclusions and Recommendations

32 06 Conclusions and Recommendations 1. The study confirm that subduction zone earthquakes have lower attenuation than crustal earthquakes. 2. The ground-motion values predicted by these equations are higher than those obtained with the crustal earthquake attenuation equations previously used. 3. Compared with the subduction zone earthquake attenuation results obtained using worldwide data by Youngs et al. (1997), the estimated ground-motion level obtained in this study is lower for all magnitudes and all periods. 4. The use of large magnitude foreign earthquake data is a temporary expedient. As more data from northeastern Taiwan become available, we need to redo this analysis. 5. Instead of a least-square method, it s necessary to use a maximum likelihood method to resolve the problem of data distribution and the mixed effect model to treat the variance reasonably.

33 Thank you for your attention.