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Date: Wed, 22 Sep 1999 11:27:44 -0500 (CDT)
X-Sender: whklee@..................
Mime-Version: 1.0
To: wehz@........................
From: William Lee 
Subject: Re: Report #1 on Taiwan EQ by Willie Lee

Dear WEHZ team members:

Attached below is my first report on the Taiwan earthquake based
on waveform data I received last night (i.e., the main shock 
waveform data from the RTD telemetered system, and from the 
building array at the CWB HQ). 

You are free to distribute this Report #1.  More with tables,
waveforms, graphs, and maps will be ready later today.

The strong-motion records from near ground zero look great -- 
up to about 1g PGA.

Willie

=============================================================

REPORT #1 on the Chi-Chi (Taiwan) Earthquake as of 6 a.m., Sept. 22

  Prepared by W. H. K. Lee with seismic data kindly provided by
Dr. K. W. Kuo, Director of the Seismology Center, Central Weather
Bureau (CWB), Taipei, Taiwan and his staff.  A preliminary note
was written by Lee on the night of Sept. 20, based on the
information received in e-mails from the CWB AutoLocation system.
This is the first report based on some seismic waveform data and
preliminary results that Lee had received from CWB.  More specific 
reports containing tables, graphs, and maps will be prepared later today.


INTRODUCTION

  A major earthquake occurred near Chi Chi in the Nantou county,
Taiwan, on 1:47 a.m., Sept. 21, local time, about 90 miles south
of Taipei.  The dead toll exceeded 1800 and is mounting, thousands
of houses collapsed making more than 100,000 people homeless.
It is a major disaster.  This big quake generated a wealth of modern
digital data for seismology and earthquake engineering, because an
extensive six-year, strong-motion instrumentation program for Taiwan
was successfully implemented 3 years ago.

  Reliable hypocenter and magnitude were determined automatically 
in about 100 seconds (after the earthquake's origin time), and I 
received this information in an e-mail, several minutes later.  
Thousands of aftershcoks have been recorded.


PGA VALUES NEAR THE EPICENTER

  Strong-motion records had been retrieved at two stations in the
epicentral area (epicentral distance of 8 and 10 km) with the
following PGA values.  Strong ground motion lasted over 30 seconds.

  Station TCU078: 0.17 g (vertical), 0.30 g (NS), and 0.44 g (EW).
  Station TCU129: 0.34 g (vertical), 0.61 g (NS), and 0.98 g (EW).


INSTRUMENTATION IN OPERATION

  In 1990, Professor Ta-Liang Teng of the University of Southern
California and Professor Yi-Ben Tsai (now at the National Central
University of Taiwan) persuaded the local government to fund
an extensive seismic instrumentation program for the urban areas
of Taiwan with mostly strong-motion instruments.  After 6 years
and about $40 million US dollars later, the Seismology Center
of the Central Weather Bureau completed the installation in 1996
of:

  (1) About 700 modern digital accelerograhs in free-field sites,
  (2) About 50 realtime seismic arrays (up to 60 accelerometers)
      in representative buildings and bridges,
  (3) A rapid earthquake information release system based on 60+
      telemetered digital accelerographs, and
  (4) A prototype earthquake early warning system in Hualien.

  This program was executed by the CWB's Seismology Center under
the direction of Dr. T. C. Shin (now Deputy Director-General of
CWB).  An advisory committee consists of about 10 seismologists
and earthquake engineers assisted CWB in the planning of the
program and the design of the instrumentation.  Cooperative
projects with the U. S. Geological Survey (1991-1995), and with
the Southern California Earthquake Center (1991-present) greatly
accelerated the implementation and the successful operation.

  Taiwan is a small island, about 8% of the area of California
or Japan.  With the above instrumentation, Taiwan operates the
densest digital strong-motion instruments of the world.  For
comparison, station spacing of the free-field accelerographs in
Taiwan is about 3 km in the metropolitan area (vs a 25-km
uniform spacing of K-Net in Japan).  The basic design of the
realtime strong-motion array system for structures has since been
implemented by PG&E for the headquarter building in San Francisco,
and is now being implemented in the Millikan Library building
of Caltech and in a building at UCLA.

  CWB's Rapid Earthquake Information Release System (AutoLocation)
began operation in March 5, 1996.  Continuously telemetered data
from 60+ digital accelerographs were automatically processed in
a dual PC-based system (for redundancy) in Taipei, using hardware and
software designed and implemented in the early 1990's (Lee et al.,
1996; Shin et al., 1996).  Early results had been published by
Teng et al. (1997), and by Wu et al. (1997).


REFERENCES

Lee WHK, Shin TC and Teng TL (1996). Design and implementation of
  earthquake early warning systems in Taiwan. Proc. 11th World Conf.
  Earthq. Eng., Paper No. 2133.

Shin TC, Tsai YB, and Wu YM (1996). Rapid response of large earthquake
  in Taiwan using a realtime telemetered network of digital
  accelerographs. Proc. 11th World Conf. Earthq. Eng., Paper No. 2137.

Teng TL, Wu L, Shin TC, Tsai YB, and Lee WHK (1997).  One minute after:
  strong motion map, effective epicenter, and effective magnitude.
  Bull. Seism. Soc. Am., vol 87, p 1209-1219.

Wu YM, Shin TC, Chen CC, Tsai YB, Lee WHK, and Teng TL (1997).
  Taiwan rapid earthquake information release system. Seism. Res.
  Letters, vol 68, p 931-943.









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