After an intensive programs to instrument urban areas during 1991

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After an intensive programs to instrument urban areas during 1991-1996, Taiwan has the highest
concentrations of modern
digital accelerographs of the world (about 5 times closer station spacing than Japan): about 1,000 digital
accelerograhs in free
sites, and an equivalence of over 500 accelerographs in structures (about 50 structures have been
instrumented with an array of
accelerometers and are monitored by a realtime system). The results reported below derived from about 70
continuously
telemetered digital accelerographs, many at the local weather stations in urban areas.
A few simple facts:
(1) Taiwan has an area of about 8% of California or Japan. More than 1/2 of the area are mountainous (up to
4,000 meters).
(2) It is very seismic active, because Philippines plate/Pacific Plate/Eurasia Plate converge there. Seismicity
is about 3-5 times
higher than California.
(3) I am fortunate to have the opportunity to participate in their earthquake program while I was at the
USGS before and after
my retirement.
(4) The Taiwan instrumentation program costed about $40 millions in 6 years (about 90% were spent on
strong-motion). It was
completed on time, under the budget (the program was budgeted at $72 million), and with only a few
additional staff from their
original staff of about 30 people.
(5) Finally, I believe the "KISS" principal works, i.e., keeping it simple.
=====Prepared by about 11 p.m, 9/20/99, Calif. time=====
Taiwan Quake: Results and Performance of Taiwan's Rapid Earthquake Information Release
System
At 1:47 a.m. Taiwan local time, a major earthquake occurred in Taiwan, about 140 km SSW of Taipei, its
capital. Fortunately,
the epicenter was located in the mountainous area, about 50 km southeast and northeast from two major
cities: Taichung and
Chiayi, respectively. Hundreds of people were killed and thousands were injured. The disaster would be
similar to the recent
Turkey quake if the epicenter were 50 km west in the coastal plain, where the population is very dense.
I received the main shock information in an e-mail, several minutes after the earthquake occurred. The
Taiwan's realtime system
is based on about 70 continuously digital-telemetered accelerographs all over the island, and has been in
operation since March
5, 1996. Data were automatically processed 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 Wu et al.
(1997). [see
References after the table].
In the following table, I listed the results received as of 10 p.m., Sept. 20, California time (or 1 p.m., Taiwan
local time), i.e., for
a period of about 11 hours after the main shock.
Several general conclusions are:
(1) The Taiwan system performed as designed and has shown to be capable of handling probably the largest
earthquake of this
century in Taiwan. The first located aftershock occurred just 10 minutes after the main shock. There were
many aftershocks and
some were quite large.
(2) The preliminary result of the main shock is reasonably accurate. The local magnitude was estimated to
be 7.3 in about 100
seconds after the earthquake's origin time and agreed well with the Mw = 7.6 determined by NEIC in about
3 hours after the
earthquake. Focal depth was 10 km vs 5 km given by the moment tensor solution of NEIC.
(3) Hypocenter and magnitude were determined in about 100 seconds after the origin time, or about 90
seconds after sufficient
number of stations recorded the first P-arrivals. Some extra time was spent in making sure that the largest
amplitudes had been
recorded. For some aftershocks, the processing time (Proc. Time in the following table) was less than 1
minute. The Proc. Time is
defined to be the elapsed time from the earthquake's origin time to the time the results sent to the e-mail
server.
(4) E-mail transit time is quick in the beginning (middle of the night), taking only several minutes to get
from Taipei to my
home. However, by 5 a.m. local time, e-mails were backed up and for several hours, no e-mails arrived from
Taiwan. Phone calls
to Taiwan are not possible at this moment (12 hours after the quake and e-mails from Taiwan started to
dribble in.
The following lists the results from the Taiwan realtime system as received in e-mails after the first 11 hours
of the quake.
Results after the first two hours are probably not complete as the e-mails could not get out of Taiwan
rapidly.
------------------------------------------------------------------Date
Origin Time Latitude Longitude Depth(Km) ML Proc. Time
------------------------------------------------------------------9/20/99 17:47:15.89 23.87 N
120.75 E
10.0
7.3
102 sec.
9/20/99 17:57:17.16 23.95 N
121.03 E
6.9
6.1
57 sec.
9/20/99 18:03:42.64 23.80 N
120.85 E
5.0
6.5
75 sec.
9/20/99 18:11:27.71 24.03 N
120.98 E
5.2
5.2
56 sec.
9/20/99 18:16:21.01 23.86 N
121.03 E
13.5
6.9
85 sec.
9/20/99 18:21:31.57 23.99 N
121.07 E
8.9
5.1
50 sec.
9/20/99 18:32:55.60 23.82 N
121.01 E
2.9
5.2
62 sec.
9/20/99 19:28:43.48 23.88 N
120.97 E
2.4
4.9
53 sec.
9/20/99 19:40:33.27 23.57 N
120.88 E
2.5
5.4
55 sec.
9/20/99 19:57:52.19 24.17 N
120.75 E
6.9
5.9
76 sec.
9/20/99 20:02:15.36 24.01 N
120.67 E
2.5
5.7
69 sec.
9/21/99 01:37:09.01 23.73 N
120.75 E
2.5
5.2
55 sec.
9/21/99 02:24:46.48 23.93 N
121.00 E
8.4
4.9
56 sec.
5.1
58 sec.
9/21/99 03:31:49.58 23.99 N 121.02 E
3.1
-------------------------------------------------------------------
Earthquake parameters were determined in real time by the Seismology Center of the Central Weather
Bureau (CWB), Taipei,
Taiwan", and "were compiled and annotated by W. H. K. Lee, an advisor to CWB
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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