Information message About the earthquake on September 20, 1999 in Taiwan

     On September 20, 1999 at 21:47 Moscow time (17:47 pm GMT) the destructive earthquake has happened in central part of Taiwan island, 160 km South-West from Taipei city.
     Parameters of the earthquake have been determined in the Alert Service (AS) of Information Processing Center (IPC) of Geophysical Survey of RAS in Obninsk with station data obtained from digital and analog seismic stations of Russia, countries of CIS and from abroad. Alert message on this earthquake has been delivered in 58 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 13 stations, accurate processing - with data 29 stations.
     IPC GS RAS also has obtained information with parameters of this event from some seismological centers, these data are given in table 1:
Table 1
NN Time in origin h-min-s (GMT) Lat degr. Lon degr. Depth km N s/st Ms/ N mb/ N I0 calc GAP Center
1 17-47-17.00 23 121  33  13  7.8/3 9-9.5 IPC GS RAS (Preliminary)
2 17-47-17.80 23 121  33  29  7.7/57.4/59-10 IPC GS RAS (Improved)
  • IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences
    • Epicenter
         Most full information on this earthquake, it's consequences and aftershocks is kept on special WEB site IRIS Consortium – “Special Event page – TAIWAN” . Here one can find references to other servers of world information centers, which issued information about this earthquake. Hypocenter location is shown on a map obtained from the WEB site of National Information Center of Geological Service of USA (USGS). The earthquake has happened in Pacific Ocean seismic belt and was caused by strike of Eurasian and Filipino plates.

    Figure 1
    Macroseismic manifestations
         Macroseismic manifestation of the earthquake on September 20, 1999 was published on Web site of Taiwan information Agency (Chine Times Interactive): on September 21: -More than 1500 people were lost and 3800 injured. Puli town located in central Taiwan and being the most close to the hypocenter has 98 percent of broken buildings. More than 1000 strikes have been registered in 18 hours right after the underground blow.
    Historical records
         Historic records on seismicity of Taiwan island are presented in details in special IRIS Consortium report – “Seismo-Watch Special Earthquake Report No. 99-022”. After the data from this report Taiwan island is classified as a zone with high level of seismicity. Nearly thousand of earthquakes happen here annually. The strongest of them before September 20, 1999 are: -Earthquake in 1935 with M=7.4, which led to numerous victims among the population (3250 people lost); -Earthquake on November 14, 1986 with M=7.8 with 15 people lost and 44 injured. This report also gives a list of events around Taiwan with M>6.5 since the year 1900.
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism and moment of seismicity, has been determined from tensor moment of centroid techniques in Harvard Geophysical laboratory (HRV solution) and National Information Center of Geological Service of USA (USGS solution); they are presented in Table 2 and in figures 1 and 2.
    HRV solutionUSGS solution
    September 20, TAIWAN, Mw=7.7
    Natasha Maternovskaya
    Erik Larson: eq@seismology.harvard.edu

    CENTROID, MOMENT TENSOR SOLUTION
    HARVARD EVENT-FILE NAME C092099A
    DATA USED: GSN
    L.P. BODY WAVES: 4S, 12C, T= 45
    MANTLE WAVES: 4S, 7C, T=135
    CENTROID LOCATION:
    ORIGIN TIME 17:47:38.2 0.3
    LAT 23.94N 0.02;LON 120.71E 0.06
    DEP 20.7 1.3;HALF-DURATION 18.8
    MOMENT TENSOR; SCALE 10**27 D-CM
    MRR= 3.37 0.08; MTT=-0.93 0.07
    MFF=-2.44 0.12; MRT=-1.54 0.18
    MRF=-1.98 0.20; MTF=-1.33 0.05
    PRINCIPAL AXES:
    1. (T) VAL= 4.22;PLG=71;AZM=133
    2. (N) -0.17; 3; 33
    3. (P) -4.05; 19; 302
    BEST DOUBLE COUPLE:M0=4.1*10**27 NP1:STRIKE= 26;DIP=27;SLIP=82
    NP2: 215; 64; 94



    Рисунок 1
    		 99/09/20 17:47:19.01
    Stuart Sipkin: sipkin@usgs.gov

    TAIWAN
    Epicenter: 23.781 121.090
    mb 6.3 MS 7.6
    MOMENT TENSOR SOLUTION
    Depth 5 No. of sta: 23
    Moment Tensor; Scale 10**20 Nm
    Mrr= 1.93 Mtt= 0.01
    Mff=-1.94 Mrt=-0.76
    Mrf=-1.20 Mtf=-0.33
    Principal axes:
    T Val= 2.44 Plg=69 Azm=138
    N 0.04 11 17
    P -2.40 17 283
    Best Double Couple:Mo=2.4*10**20
    Mw=7.6
    NP1:Strike=357 Dip=29 Slip= 67
    NP2: 202 63 102







    Рисунок 2
    Average value of seismic moment Мо for this earthquake, which has been determined in IPC GS RAS by spectra of Р-waves at three stations: Talaya (delta=30.9o), Arti (delta=55.4o), Obninsk (delta=67.8o), made 1.5*10**20 n*m (1.5* 10**27 D-CM). The value of moment magnitude made Mw =7.4.
    Table 2
    Axes of main strengths Nodal planes Center
    T P N NP1 NP2
    Pl Azm Pl Azm Pl Azm Stk Dp Slip Stk Dp Slip
    6913817283 11173572967202 63102NEIC
    7113319302 333262782215 6494HARVARD
  • NEIC - National Earthquakes Information Center of US Geological Service
  • HARVARD - Harvard Geophysical Center (USA)


    • News | Catalogs | Wave Forms | Alert Service | Software | Links | Srtucture | Publications | Conferences | Announce | About
    © FRC GS RAS 1993-2018