A Refined Vs30 Map for Taiwan Based on Ground Motion Attenuation Relationships

Abstract

Seismic hazard evaluations require an estimate of the expected ground motion at the site of interest usually by using attenuation relationships. The mean shear-wave velocity over the top 30 m (Vs30) is incorporated in the ground motion attenuation relationships in this study. By comparing the standard deviations of the residuals between the observed and predicted values before and after incorporating the site effect term Vs30, the reduction in standard deviation for the peak ground velocity (PGV) is significantly reduced by about 11%. Clearly, the refined attenuation relationships will be more useful for engineering purposes. Analyzing the site effect term using the amplification factor (relative to a site with Vs30 = 760 m s-1), has revealed that the Changhua Plain, Chianan Plain, Pingtung Valley, Ilan Plain, and Taipei Basin have high values, implying large ground motion amplification. Following a disastrous earthquake, quick assessment and timely peak ground acceleration (PGA) and PGV map reporting will be critical for effective emergency response operations. After an earthquake we can combine the simple attenuation relationships, as determined from Model 1, to provide near real-time estimation and reporting of the PGA and PGV values for the Taiwan area. We can also use the relations between the intra-event site residual and the Vs30 to estimate the Vs30 for stations that have recorded strong motions, but do not yet have Vs30 information. Our approach including sites with estimated Vs30 has resulted in a refined Vs30 contour map that can be used for more realistic seismic hazard assessment for Taiwan. This approach is especially applicable to the foothill and mountain areas.

A horizontal ground-motion model for crustal and subduction earthquakes in Taiwan

“…Several ground-motion models have been proposed for Taiwan over the past decade (Chang et al, 2001, 2012; Chen and Tsai, 2002; Chung, 2006; Jean et al, 2006; Kao et al, 2010; Lin et al, 2011a, 2011b; Lin and Lee, 2008; Liu et al, 2013, 2014; Liu and Tsai, 2005, 2015; Loh et al, 1991; Niazi and Bozorgnia, 1991, 1992; Sokolov et al, 2010; Tavakoli and Pezeshk, 2007; Tsai et al, 2006; Wang et al, 2004, 2016; Wu et al, 2001). However, these models have limited engineering applications for PSHA for the following reasons:…”

Estimation of Seismic Ground Motions and Attendant Potential Human Fatalities from Scenario Earthquakes on the Sanchiao Fault in Taipei City, Taiwan

“…In this study the site effects are included in the ground motion prediction model by a site response factor at each grid point. These predictive relationships were obtained by using the Taiwan Strong Motion Instrumentation Program (TSMIP) network data operated by the CWB of Taiwan to estimate peak ground motion at all grid points [6,17,18]. The TSMIP network has been designed to enhance the ability to monitor strong earthquakes and to collect high-quality instrumental recordings of free-field ground shaking [4,5,19].…”

“…Alternatively, the site effect was corrected in this study by a site response factor at each grid point. At first, these predictive relationships are used to estimate peak ground motion for each grid point, and then correct the amplitude at that location using a site response factor determined by Liu and Tsai [6,18]. The site response factor r is defined as the difference between the logarithms of the observed and the predicted ground motion.…”

“…The site response factor r is defined as the difference between the logarithms of the observed and the predicted ground motion. The site amplification values can be calculated from exp (r) [6].…”

“…In addition, some Scenario Earthquakes on the Sanchiao Fault in Taipei City, Taiwan studies estimated potential seismic hazards in southern Taiwan in the form of ShakeMaps. Particularly, the site response factor is incorporated into their ground motion prediction models to obtain more realistic peak ground motion estimates for assessment of potential seismic hazards [3][4][5][6][7].…”