Nai-Chi Hsiao

Relationship between Peak Ground Acceleration, Peak Ground Velocity, and Intensity in Taiwan

Based on the strong-motion data set from the 1999 Chi-Chi, Taiwan, earthquake and a shaking damage statistics database, we investigated the correlations between strong ground motions and earthquake damage (fatalities and building collapses) through a regression analysis. As a result, the current earthquake intensity scale I t is placed on a more reliable instrumental basis. This is necessary for the real-time seismic monitoring operation in Taiwan where programs for earthquake rapid reporting (RRS) and earthquake early warning (EWS) are actively pursued. It is found that the earthquake damage statistics give a much closer correlation with the peak ground velocity (PGV) than with the peak ground acceleration (PGA). The empirical relationship between PGV and the intensity I t determined in this study can be expressed as \[I_{\mathrm{t}}=2.14{\times}\mathrm{log}_{10}(\mathrm{PGV})+1.89.\] This PGV-based intensity is particularly useful in real-time applications for damage prediction and assessment, as the damage impact of high PGV is much more important for mid-rise and high-rise buildings that are characteristic of a modern society. For smaller earthquakes ( M M

Development of earthquake early warning system in Taiwan

[1] With the implementation of a real-time strong-motion network by the Central Weather Bureau (CWB), an earthquake early warning (EEW) system has been developed in Taiwan. In order to shorten the earthquake response time, a virtual sub-network method based on the regional early warning approach was utilized at first stage. Since 2001, this EEW system has responded to a total of 225 events with magnitude greater than 4.5 occurred inland or off the coast of Taiwan. The system is capable of issuing an earthquake report within 20 sec of its occurrence with good magnitude estimations for events up to magnitude 6.5. Currently, a P-wave method is adopted by the CWB system. Base on the results from 596 M > 4.0 earthquakes recorded by the real-time strong-motion network, we found that peak displacement amplitudes from initial P waves (P d ) can be used for the identification of M > 6.0 events. Characteristic periods τ c and τ max p of the initial P waves can be used for magnitude determination with an uncertainty less than 0.4. We expect to achieve a 10-second response time by the EEW system in Taiwan in the near future.

State of the Art and Progress in the Earthquake Early Warning System in Taiwan

We report here the recent progress and future development of real-time seismic monitoring in Taiwan, especially on earthquake early warning system (EWS) developed at the Central Weather Bureau (CWB), using the telemetered signals from strong-motion instruments. Utilizing a quick magnitude determination based on the first 10 sec of signals from a virtual and sub-network which is configured automatically, we were able to reduce the earthquake rapid reporting time to about 30 sec or less. This represents a significant step towards a more realistic earthquake early warning capability. This early warning system has been in operation at CWB since 2002. Comprehensive earthquake reports have been issued mostly in less than 30 sec, with an average of about 22 sec from the origin time. At 3 km/sec for a typical crustal shear-wave velocity, the present operation is not useful if an earthquake occurs less than about 70 km from a city, but the lead time will increase to more than 10 sec for cities at distances greater than 100 km from the earthquake source. In the latter case, a lead time of several seconds will allow pre-programmed emergency response to take place prior to the arrival of strong ground shaking. In order to offer earlier warning within an epicentral distance of less than 70 km, a τc and Pd method was experimented. We used the Taiwan Strong-Motion Instrumentation Program (TSMIP) accelerograms recorded within epicentral distances of less than 30 km from Mw > 5.0 crustal earthquakes. This method uses the first 3-sec length records from the onset of P-waves and could issue an on-site early warning within 10 sec after the event origin time, reducing the radius of the blind zone from 70 to 25 km from the epicenter.

On the Establishment of an Automatic Earthquake Information Broadcast System in Taiwan

An efficient earthquake auto-location algorithm has been developed by the Central Weather Bureau (CWB), Taiwan. The CWB can now routinely obtain earthquake information in one minute after the occurrence of an earthquake using this new algorithm. In order to take full advantage of this capability, four automatic information broadcast media, namely, e-mail, World Wide Web, FTP server and pager system, have been configured to receive and transmit automatically the earthquake information from the CWB seismic monitoring system. This new automatic earthquake information broadcast system will enable the CWB to disseminate information about felt earthquakes even more quickly and widely than its current practice through the fax and paper reports.