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On September 21, 1999, an earthquake in Taiwan killed more than 2,400 people, destroyed or damaged thousands of buildings and left an estimated 100,000 people homeless. It was the worst earthquake to hit Taiwan–where quakes are common due to its location in a seismically active zone of the Pacific basin—since a 1935 tremor that killed more than 3,200 people.
At 1:47 a.m. on September 21, 1999, the island of Taiwan, located off the southeastern coast of mainland China, was shaken by a 7.6-magnitude earthquake. Its epicenter was located in Nantou County in central Taiwan, but serious damage occurred across the island. More than 2,400 people were killed, while more than 11,000 others were injured and thousands of buildings were destroyed or damaged. Roads buckled, bridges collapsed and landslides diverted rivers, causing the impromptu formation of lakes. There was not enough freezer capacity in the country’s morgues to hold all the bodies.
Buildings all over the island proved to be vulnerable. Several tall buildings in Taiwan’s capital city, Taipei, located 90 miles north of the quake’s epicenter, were toppled. The quake exposed the fact that shoddy construction had occurred during Taiwan’s building boom in the 1990s. Tent cities popped up in fields and parks because many people were afraid of being in buildings while aftershocks continued. Overall, the disaster (which became known locally as the 921 earthquake, because it occurred on September 21) caused billions of dollars in economic losses.
In 2001, the 921 Earthquake Museum of Taiwan opened in the city of Taichung, an area affected by the 1999 earthquake.
Suicide trends following the Taiwan earthquake of 1999: empirical evidence and policy implications
Objective: Mental health impact of severe earthquakes on survivors has attracted considerable attention. Suicide represents a terminal outcome of the spectrum of potential major mental health issues spawned by severe earthquakes. This study used time-series analysis to examine the time trends of increased suicide rates after the Chi-Chi earthquake of 1999 in Taiwan in the affected counties.
Method: Adult cause of death data were used to study monthly suicide rates per 100,000 adult population in the study and control counties, during January 1995 to December 2001. Box and Tiao's event intervention analysis was used to examine changes in monthly suicide rates before and after the Chi-Chi earthquake.
Results: During the post-quake period, October 1999 to December 2001, the mean monthly suicide rate in the affected counties was 1.567 per 100,000, compared with the control counties' rate of 1.297 per 100,000. Mean monthly suicide rate among the high-exposure group was 42% higher during the 26 months following the earthquake than the average for the entire observation period. Examined by time trends, the increased suicide rate registered in the first month following the quake began a monthly gradual decline by 0.7/100,000 thereafter, accounting for a total reduction of 98% in quake-related suicides by the end of 10 months. Suicide rates fell to the baseline level after 10 months.
Conclusion: We found that the mean monthly suicide rate for earthquake victims was higher while the low-exposure group remained stable and consistent throughout the observation period, indicating that the impact on the high-exposure group was attributable to the earthquake. This indicates the need for providing strengthened psychiatric services during the first year following major disasters.
1999 Taiwan earthquake - HISTORY
The Earthquake of 20 September 1999 in Taiwan
George Pararas Carayannis
A large earthquake struck the island of Taiwan at approximately 1:45 a.m. (local time) on September 20, 1999. The quake killed or injured thousands of people, left thousands more homeless and caused extensive destruction to buildings, roads and utilities. Most of the casualties and damage occurred in the central Nantou, Taichung and Yunlin Counties. The quake triggered a series of landslides.
Date and Time of Origin: A complex, earthquake struck Taiwan on 20 September 1999. Origin time was 17:47 (09 20 UTA)
Epicenter: The epicenter was at 18.6 23.804N 120.958E. 90 miles south of Taipei, near the central city of Taichung,
Focal Depth: Shallow.
Afteshocks: Major aftershocks measuring as much as 6.8 and 6.3 on the Richter scale occurred the day after the major quake. More than 2,000 aftershocks were recorded in the days following the main shock.
Damage to government building
Seismotectonic Setting - Tectonic Dynamics and Plate Interaction in the Taiwan Region
The plate tectonic systems in the region near Taiwan where this earthquake occurred are extremely complex and have changed considerably throughout geologic time. The tectonic setting and the dynamics of interaction have been extensively discussed in the literature (see references below).
The island of Taiwan is located on the convergent boundary between the Eurasian and the Philippine Sea tectonic plates. Presently, and during the Plio-Pleistocene period, principal tectonic plate interaction in the vicinity of Taiwan, has been closely related to the Ryukyu and Luzon arc-trench systems, characterized by subduction, convergence and rotation, but marked primarily by the collision of the Luzon volcanic arc with the Asian continental margin.
Also, there has been apparent northward subduction of the Philippine Sea plate beneath the Ryukyu arc on the Eurasian plate along the Ryukyu Trench. The Ryukyu arc is to the east and northeast of Taiwan while the Luzon Arc System is south of Taiwan (see figure). Both volcanic arcs extend onto the island of Taiwan.
The tectonic interactions are extremely complex. In the vicinity of Taiwan, They both subduction and plate convergence take place but not along a simple plate boundary or subduction zone as it would be commonly conceived, and this is due to the difficulty of subducting a portion of the continental crust which is markedly buoyant. Apparently, a wide distributed shear system developed during different stages of the arc-continent collision.
Earlier tectonic plate convergence in the vicinity of Taiwan was marked by an apparent eastward subduction of the Eurasian plate underneath the Luzon arc on the Philippine Sea plate. However, this shear motion moved westward with time, forming a broader zone of deformation involving subduction, collision, and plate consumption, rather than a discrete well-defined plate boundary. On Taiwan, this wide belt of deformation extends for about 100 km from the western to the eastern offshore region of the island.
(U.S.G.S map of the earthquake's epicenter, other earthquake epicenters, and tectonic plate boundaries)
This active, complex and ever changing tectonic interaction and collisions along a wide deformation belt, have affected the entire island of Taiwan and have created in the past the Central Mountain Range, known as the Penglai orogeny and the Longitudinal Valley of eastern Taiwan, both areas of high seismicity.
The Central Range is characterized by fast uplift at a rate of 2-3 cm/yr or more and fast tilting at both lambs of the mountains, the west end tilting westward of about 1.0µ radian/yr while the east of about 3.0 µ radian/yr. Both regions are characterized by the widespread distribution of shallow-focus earthquakes. The earthquake of September 1999, had its epicenter in this zone of Central Taiwan - thus no tsunami was generated.
Assessment of Tsunami Generation from Earthquakes in the Taiwan and the Southern Ryukyu Islands Region
As already described, Taiwan is located on the convergent boundary between the Eurasian and the Philippine Sea tectonic plates, a region characterized by subduction, convergence, rotation, and collision of the Luzon volcanic arc with the Asian continental margin. BothThe Ryukyu arc is to the northeast, and the Luzon Arc System to the south, converge onto Taiwan.
Northward subduction of the Philippine Sea plate beneath the Ryukyu arc on the Eurasian plate along the Ryukyu Trench can generate, large potentially tsunamigenic earthquakes. According to old Japanese records, on April 24, 1771, a large earthquake (with an estimated Richter magnitude of 7.4) occurred near the southermost Ryuku Islands, just south of Ishigaki Island, an area controlled then by the Japanese Satsuma samurais.
A tremendous tsunami was generated according to old records. Claims of maximum runup of 50m to 85m have veen made. Tsunami devastated the islands of this group and the more distant islands of the Miyako group. Huge blocks of coral were carried by wave action. A large coral block was found 2.5 km inland. Claims were made that the block was not a remnant of erosion but that it was deposited by a tsunami wave. Records of the Satsuma samurais indicate that about 11,000 people were killed in the southern Ryukyu islands. The tsunami effects in Taiwan, Hong Kong and elsewhere in the region are not known.
Ishigaki, Ryukyu Islands.
Assessment of Tsunami Generation from Earthquakes in the Taiwan Strait
None of the earthquakes with epicenter on the island of Taiwan are not known to have generated tsunamis. However, earthquakes with epicenters near or in the sea can generate tsunamis along the coast of Taiwan and of mainland China. The most recent large earthquake (mb=6.5), in the Taiwan Strait occurred on 16 September 1994 in the western part of the Tainan basin, at a very shallow depth of 13 km. It was named Peng-Hu Earthquakesk. The quake's focal mechanism indicated a sea floor movement consistent with normal faulting, with its axis along a N-S direction.
The occurrence of this earthquake indicates that the Taiwan Strait is seismically active and capable of generating earthquakes with Richter magnitudes greater than 6.0. Although it is not believed that this particular earthquake generated a tsunami, earthquakes with magnitude greater than 6 on the Richter scale have the ability to trigger tsunamis, while earthquakes with magnitude greater than 7 and with a large vertical component, have the ability to generate destructive tsunamis.
The orientation of the crustal strain beneath the Taiwan Strait appears to be dominated by North-South extension rather than the East-West compression that is observed along eastern Taiwan. Given the complex tectonic interactions of the region, tsunami generation is possible. The tsunami risk for the Taiwan Strait requires careful evaluation and study.
REFERENCES AND FURTHER READING
Angelier J., Bergerat F., Chu H.-T., Juang W.-S. and Lee T.-Q. (1990). Tectonic-paleomagnetic analyses and the evolution of a curved collision belt : the Hsueshan Range, northern Taiwan. Tectonophysics, 183, 77-96.
Angelier, J., H.T. Chu and J.C. Lee (1997). Shear concentration in a collision zone: kinematics of the active Chihshang Fault, Longitudinal Valley, eastern Taiwan: Tectonophysics, 274, 117-144.
Chen, W.-P. and H. Kao (1996). Seismotectonics of Asia: some recent progress: in The Rubey Volume IX: Tectonic Evolution of Asia, edited by A.Yin and M. Haarrison, 37-62, Cambridge Univ Press.
Chen, K.J., Y.H. Yeh, H.Y. Yen and C.H. Lin (1995). Seismological studies in the Chinshan fault area: J. Geol. Soc. China, 38(4), 335-354.
Davis, D., J. Suppe, and F.A. Dahlen (1983). Mechanics of Fold-and-Thrust Belts and Accretionary Wedges, J. Geophys. Res., 88, 1153-172.
Delcaillau, B., J. Deramond, P. Souquet, J. Angelier, H.T. Chu, J.C. Lee, T.Q. Lee, T.F. Lee, P.M. Liew and T.S, Lin (1994). Enregistrement tectono-sedimentaire de deux collisions dans l'avant pays nord-occidental de la chaine de Taiwan. C.R. Sci. Acad. Paris, t318, series II, 985-991.
Deramond, J., Delcaillau, B., P. Souquet, J. Angelier, H.T. Chu, J.F. Lee, T.Q. Lee, P.M. Liu, T.S, Lin and L. Teng (1996). Signatures de la surrection et de la subsidence dans les bassins d'avant chaine actifs: les Foothills de Taiwan (de 8 Ma a l'Actuel): Bull. Soc. Geol. France, 167(1), 111-123.
Hu, J.C., J. Angelier, J.C. Lee, H.T. Chu and D. Byrne (1996). Kinematics of convergence, deformation and stress distribution in the Taiwan collision area: 2-D finite-elememt numerical modelling: Tectonophysics, 255, 243-268.
Kao, H. (1998). Can great earthquakes occur in the southernmost Ryukyu arcúTaiwan region?: TAO, 9(3),487-508.
Kao, H., S. J. Shen and K.F. Ma (1998) .Transition from oblique subduction to collision: Earthquakes in the southernmost Ryukyu arcúTaiwan region: J. Geophys. Res., 103(B4), 7211-7229.
Kao, Honn and Francis T. Wu (1996). The 16 September 1994 earthquake (mb=6.5) in the Taiwan Strait and its tectonic implication: TAO, 7(1), 13-29.
Lee, J.C., J. Angelier and H.T. Chu (1997). Polyphase history and kinematics of a complex major fault zone in the northern Taiwan mountain belt: the Lishan Fault: Tectonophysics, 274, 97-116.
Lee T.-Q., Angelier J., Chu H.-T. and Bergerat F. (1991). Rotations in the northeastern collision belt of Taiwan: preliminary results from paleomagnetism. Tectonophysics, 199, 109-120.
Lu C.-Y., Angelier J., Chu. H.-T. and Lee, J.-C. (1995). Contractional, transcurrent, rotational and extensional tectonics: examples from Northern Taiwan: Tectonphysics, 246, 129-146
Lu, C.Y., S.B. Yu and H.T. Chu (1998). Neotectonics of the Taiwan mountain belt: AGU Monograph, Geodynamics, 27, 301-315.
Lu, C.Y., H.T. Chu and J.C. Lee (1997). Structural evolution in the Hsuehshan Range, Taiwan: J. Geol. Soc. China, 40(1), 261-279.
Lue, Y.T., T.Q. Lee and Y. Wang (1995). Paleomagnetic study on the collision-related bending of the fold-thrust belt, northern Taiwan: J. Geol. Soc. China, 38(3), 215-227.
Yeh Y.-H., Barrier E., Lin C.-H. and Angelier J. (1991). Stress tensor analysis in the Taiwan area from focal mechanisms of earthquakes. Tectonophysics, 200, 267-280.
Yen, H.Y., W.T. Liang, B.Y. Kuo, Y.H. Yeh, C.S. Liu, D. Reed, N. Lundberg, F. C. Su and H.S. Chung (1995) . A regional gravity map for the subduction-collision zone near Taiwan: TAO, 6(2), 233-250.
Yu, S.B. and H.Y. Chen (1994). Global Positioning System measurements of crustal deformation in the Taiwan arc-continent collision zone: TAO, 5(4), 477-498.
Wang, C.Y., A. Ellwood, F.T. Wu, R.J. Rau and H.Y. Yen (1996). Mountain-building in Taiwan and the critical wedge model: in Subduction: Top to bottom, G. E. Bebout, D. W. Scholl, S. H. Kirby, and J. P. Platt (Editors), AGU Geophysical Monograph 96, 49-55.
Wu, F.T., R.J. Rau and D.H. Salzberg (1997) . Taiwan orogeny: Thin-skinned or lithospheric collision: Tectonophysics, 274, 191-220.
Learning about earthquakes in Taiwan
The Central Weather Bureau (CWB) in Taiwan researches seismology, meteorology and provides earthquake reports. CWB also reports on sea conditions and makes astronomical observations. (1)
In a previous Open Access Government article from Deputy Director of the Seismological Center Central Weather Bureau (CWB) in Taiwan, we find out how the country’s quick earthquake alert system provides notification when it comes to ensuring disaster risk reduction.
“Several hazard earthquakes have occurred during our history. The most famous one was the 1999 Chi-Chi earthquake with Richter magnitude 7.3 in the middle of Taiwan, which killed more than 2,000 and caused mass building damage as well. The threat of an earthquake is, therefore, a serious issue today in Taiwan.”
Earthquake Early Warning System (EEW)
In the same article, we also find out that the CWB developed the Earthquake Early Warning System (EEW) to detect significant earthquakes quickly. This means that a warning can be issued about 10-15 seconds after the earthquake occurs. Alerts can be issues around 60 km away from the epicentre and as such, give seconds to 10s of seconds warning prior to the destructive shaking occurring. Nai-Chi Hsiao, Deputy Director of the Seismological Center Central Weather Bureau (CWB) explains more about the EEQ during the last five years, in his own words.
“Since 2014, CWB has provided the EEW warning directly to all the public schools, hazard-rescue agencies and other government departments in Taiwan. Since 2016, CWB has issued EEW warnings through the Public Warning System (PWS) to wireless devices of the general public. The PWS was developed and constructed by the government and communication Corp., which is based on the Cell Broadcast Service (CBS) on the 4G network. This means that all the people in high-risk area can receive an EEW warning at the same time! CWB also collaborates with TV companies to deliver instant live pop-up messages during the transmission of programmes.” (2)
The causes of earthquakes
Perhaps it is worth taking a step back now to briefly look at precisely what the causes of earthquakes are. According to the CWB, earthquakes can either be man-made, or they occur naturally. Generally speaking, we tend to experience naturally occurring earthquakes which can be divided into these areas:
- Tectonic earthquakes
- Volcanic earthquakes and
- Impacting earthquakes (like those caused by the impact of meteorites).
Among all these causes, earthquakes for the main part produced by crustal deformation (tectonic earthquakes), caused by plate movement, according to the CWB. On the CWB’s website, we find out more about the science behind earthquakes.
“Rock layers are stressed by pressures in the Earth. When the stress is stronger than the strength that the rock layer can withstand, the rock layer will move outward (dislocation). Such dislocations release a great deal of energy, producing elastic waves called seismic waves. When seismic waves reach the surface of the Earth, they cause shaking, also known as (an) earthquake.”
The real-time seismic network in Taiwan
Another important area the CWB highlights on their website concerns the establishment of the real-time Central Weather Bureau Seismic Network (CWBSN) in 1994. We know that observation stations distributed over Taiwan as well as in Kinmen, Lanyu, Penghu and Pengjiayu are part of this network. As part of this network, instruments are installed in every real-time monitoring stations which have a three-component (vertical, north-south, and east-west) short-period seismograph. We read more about this fascinating aspect of CWB’s on their website, which is extracted below.
“The ground motion signals recorded at these stations are digitally transmitted to the Central Weather Bureau by leased line and are stored for real-time processing, analysing, and archiving. If the earthquake is felt, the operating personnel will immediately release an earthquake announcement. All real-time signals are displayed in the analogue recorder at the centre, and it is convenient for the staff to check whether or not the earthquake information automatically determined by the real-time processing is correct. The digital data will be filed manually to form a data bank, which will be advantageous for future enquires.”
While earthquakes are worthy of many more articles, we can gain encouragement from the fact that through means of the mass media, convenient telecommunication equipment and the Internet, the general public is alerted about earthquake information as soon as possible. (3)
To find out more about earthquakes in Taiwan, I can highly recommend you spend time browsing through frequently asked questions on the topic, here.
1999 Taiwan earthquake - HISTORY
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Slip history and dynamic implications of the 1999 Chi-Chi, Taiwan, earthquake
 We investigate the rupture process of the 1999 Chi‐Chi, Taiwan, earthquake using extensive near‐source observations, including three‐component velocity waveforms at 36 strong motion stations and 119 GPS measurements. A three‐plane fault geometry derived from our previous inversion using only static data [ Ji et al., 2001 ] is applied. The slip amplitude, rake angle, rupture initiation time, and risetime function are inverted simultaneously with a recently developed finite fault inverse method that combines a wavelet transform approach with a simulated annealing algorithm [ Ji et al., 2002b ]. The inversion results are validated by the forward prediction of an independent data set, the teleseismic P and SH ground velocities, with notable agreement. The results show that the total seismic moment release of this earthquake is 2.7 × 10 20 N m and that most of the slip occurred in a triangular‐shaped asperity involving two fault segments, which is consistent with our previous static inversion. The rupture front propagates with an average rupture velocity of ∼2.0 km s −1 , and the average slip duration (risetime) is 7.2 s. Several interesting observations related to the temporal evolution of the Chi‐Chi earthquake are also investigated, including (1) the strong effect of the sinuous fault plane of the Chelungpu fault on spatial and temporal variations in slip history, (2) the intersection of fault 1 and fault 2 not being a strong impediment to the rupture propagation, and (3) the observation that the peak slip velocity near the surface is, in general, higher than on the deeper portion of the fault plane, as predicted by dynamic modeling.
3. Fault Geometry and Method
 All subfaults have the same dimension of 3.8 × 3.7 km, which is compatible with our static-only inversion ( Part I ) and with several previous studies [e.g., Ma et al., 2001 Chi et al., 2001 ]. Even though three fault planes are subdivided into a total of 360 subfaults, not all of them are used to generate the synthetic response. In Part I we confirmed a physically plausible assumption that slip was limited to the surface of a “wedge-shaped” block and not to subfaults below the intersection of the planes in the north and south (see Figure 2). Thus we set the slip amplitudes of the subfaults below the wedge surface to zero. The number of contributing subfaults is then limited to 324, and the number of entire free parameters is only 1620.
Materials and Methods
This devastating earthquake that hit Taiwan was centred near the Taichung region. It is the largest metropolitan area in central Taiwan, with a total population of approximately 4 million people. The earthquake mainly struck the 22 municipalities on the East side of this metropolitan area, and left the 46 municipalities on the West side virtually unaffected. The central government provided national disaster assistance to these 22 municipalities, referred to in this study as the ‘affected’ area. The other 46 municipalities are defined as the ‘unaffected’ area, and serve as the control for the pre-post area level comparison.
Study population and record linkage
The study population includes 3 432 705 people aged ⩾15 years living in the Taichung metropolitan area at the time of the earthquake, as identified through the government-maintained Family Registration file. This database provides relatively accurate demographic information on residents, such as age, gender, and the level of urbanization for each municipality.
Within the study population, death certificates were used to identify those who committed suicide during the study period. Suicide attempts are not identified in the available data and are therefore not included in the study. Death certificates, managed by the Department of Health in Taiwan, contain basic information on each deceased individual such as age, gender, date of death, and the underlying cause of death. Death certificates from 1998 to 2000 were used. Since it is a national registry of all deaths in Taiwan, we were also able to trace all deaths among study subjects who moved out of the central Taiwan area during the study period. About 0.1% of deaths could not be matched to a family registration record. The accuracy of suicide coding is relatively high, as all deaths resulting from accidents or violence (International Classification of Diseases, Ninth Revision, Clinical Modification E800–E999) in Taiwan must be jointly confirmed by a district attorney and a forensic specialist (or coroner).
The other three administrative data sets—the Victims Data File, the Enrolment File, and the Major Diseases File, are managed by the Bureau of National Health Insurance (BNHI). The Bureau issued quake cards to the 301 327 individuals among the 3 432 705 residents who lost co-resident family members, were injured, or experienced property damage. This card exempted them from the cost-sharing amount required under the National Health Insurance programme (NHI). The Victims Data File tracks basic information on cardholders and allowed the identification of the victims from the overall population. However, no information regarding the severity of injury or property loss is available in the Victims Data File. The ‘quake card’ recipients in this metropolitan area are referred to in this study as the victims. All remaining individuals in the study population are referred to as non-victims, and serve as the control group for the individual-level comparison in this study. Victims comprised 24% of the population in the affected area (272 786 victims/1 155 103 residents in the affected area = 0.24). However, not all victims resided in the affected area. A few collapsed buildings located in the unaffected area (46 municipalities) were found after the earthquake, although this area remained mainly undamaged by the earthquake. Victims only comprised 1% of the population in the unaffected area (28 541 victims/2 277 602 residents in the affected area = 0.01).
The Enrolment File was used to provide pre-quake socioeconomic and disability status information on the study subjects. NHI enrolment is mainly through employment wage tax deduction for people with a well-defined monthly wage, and through head-tax financing on farmers, fishermen, and people without a well-defined monthly wage. People with a well-defined monthly wage were classified into three categories: ⩾New Taiwanese Dollar (NT$)40 000, NT$20 000–NT$39 999, and <NT$20 000. The results remained unchanged when classified into five or seven categories. People without a well-defined monthly wage were categorized into two groups: (1) agriculture and fishery workers, and (2) individuals that were enrolled in the BNHI through local government offices. The individuals who registered their residence as being in central Taiwan, but who enrolled through other BNHI branches, were classified into a different group. This pre-quake socioeconomic status (SES) variable had six categories in total. Dependants of those insured were classified in the same categories as the insured. As part of the welfare programme in Taiwan, the government provides a premium subsidy to individuals with physical disability, so therefore we were able to identify an individual’s pre-quake physical disability status from the NHI enrolment file. The Major Diseases File was used to identify individuals with major diseases or injuries before the earthquake. In Taiwan, people with specific major diseases or injury can apply for a ‘major disease/injury card.’ Cardholders are exempted from the cost-sharing required under the NHI programme. Based on the Injury Severity Index, the NHI major disease list includes 30 major disease or injury types such as cancer, end-stage renal disease, chronic psychotic disorder, cirrhosis of the liver, acquired immunodeficiency syndrome, and schizophrenia. 42 This study used the ownership of a major disease/injury card to determine an individuals’ pre-quake health status. The individual characteristics (ownership of a major disease card, physical disability status, SES) of study subjects in September 1999 were used to represent their pre-quake characteristics.
The linkage of data sets was conducted by the Bureau using personal identification numbers and birthdays. About 2.8% of records in the NHI data could not be matched to a record in the family registration file. The administrative data sets are relatively more reliable than the NHI claims data. The final results remained the same after excluding those central region residents who were not enrolled in the Central Branch of the Bureau. This study was reviewed and funded by the BNHI. We have abided by the Bureau’s strict regulations regarding data release and the protection of privacy and confidentiality.
We observed suicide rates from the pre-quake period (1 January 1998–20 September 1999) and the post-quake period (1 November 1999–31 December 2000). Since we were unable to distinguish victims from non-victims in October 1999, as the issuance of quake cards only started on 26 October 1999 and continued throughout the entire month, we excluded the month of October 1999 from the study period. Government assistance to quake card recipients took effect on 1 November 1999. Since death and emigration information for 1998 and 1999 are available in the Family Registration Data, this study was able to retrospectively calculate suicide rates in the pre-quake period.
Study design and statistical analysis
The study design for the area-level comparison is a pre-post design with a control group, and for the individual-level comparison it is a retrospective population cohort study. The data were structured such that there was one record per individual. One suicide event per 100 000 person-years was used to calculate the suicide rate for the area-level comparison. For individual-level analysis, logistic regression was used to estimate the odds ratios (OR) for suicide with the statistical program STATA. Given the low prevalence of suicide as a cause of death, OR will have the same value as rate ratios or relative risks. 43
1999 Taiwan earthquake - HISTORY
We investigate the rupture process of the 1999 Chi-Chi, Taiwan, earthquake using extensive near-source observations, including three-component velocity waveforms at 36 strong motion stations and 119 GPS measurements. A three-plane fault geometry derived from our previous inversion using only static data [, 2001] is applied. The slip amplitude, rake angle, rupture initiation time, and risetime function are inverted simultaneously with a recently developed finite fault inverse method that combines a wavelet transform approach with a simulated annealing algorithm [, 2002b]. The inversion results are validated by the forward prediction of an independent data set, the teleseismic P and SH ground velocities, with notable agreement. The results show that the total seismic moment release of this earthquake is 2.7 × 10 20 N m and that most of the slip occurred in a triangular-shaped asperity involving two fault segments, which is consistent with our previous static inversion. The rupture front propagates with an average rupture velocity of ∼2.0 km s -1 , and the average slip duration (risetime) is 7.2 s. Several interesting observations related to the temporal evolution of the Chi-Chi earthquake are also investigated, including (1) the strong effect of the sinuous fault plane of the Chelungpu fault on spatial and temporal variations in slip history, (2) the intersection of fault 1 and fault 2 not being a strong impediment to the rupture propagation, and (3) the observation that the peak slip velocity near the surface is, in general, higher than on the deeper portion of the fault plane, as predicted by dynamic modeling.
Historic Surface Faulting
Surface faulting occurred at six different places in Taiwan prior to 1999, in association with five earthquakes whose magnitudes ranged from 6.75 to 7.3. Locations of these fault ruptures are shown on Figure 1, and the surface parameters, along with associated earthquakes and other information, are listed in Table 1 (from Bonilla, 1977).
Table 1. Historic surface faulting in Taiwan
* Two separate ruptures occurred at approximately the same time.
Figure 1. Map of Taiwan showing faults that cut Quaternary deposits. From Bonilla (1977, fig. 1). Surface ruptures (heavy lines) occurred in 1935 on faults numbered 14 and 19 in 1906 on fault number 26 in 1946 on fault 30 and in 1951 in eastern Taiwan on faults numbered 43 (October ) and 42 (November). Alignments of epicenters (pattern of dots) at 44A (Tsai and others 1975) and 45 (Tsai and Chiu 1976) indicate concealed historically active faults. Letters A-Q and their associated numbers should be ignored as they relate to a preliminary estimate of rates of Holocene uplift.
Suicides after the 1999 Taiwan earthquake
Background: The impact of a disaster on extreme post-traumatic responses of the victims, such as suicide, remains unclear. We conducted this study to investigate the risk of committing suicide between victims and non-victims after the 1999 Taiwan earthquake.
Methods: This population cohort study linked the National Health Insurance files, family registration, and death certificates. It consists of the 3 432 705 residents aged >/=15 years of central Taiwan, 1998-2000. They were stratified into victims (n = 301 327) and non-victims (n = 3 131 378). Victims refer to those who lost co-resident family members, were injured, or experienced property loss during the earthquake. Non-victims refers to all others. The suicide rate was calculated for the period 2-15 months after the earthquake. Adjusted odds ratios were estimated with logistic regression.
Results: After adjusting for residential location, age, gender, major disease status, and level of urbanization, we found that victims were 1.46 times more likely than non-victims to commit suicide following an earthquake (95% CI: 1.11, 1.92).
Conclusions: Given the large study population and individual information available to identify victim status, this study was able to detect a statistically significant earthquake effect on suicide rate. This effect on suicide might be diluted if only geographically based stratification were possible, as opposed to victim status stratifications. Mental health programmes or other preventive strategies might be more effective by specifically targeting victims rather than by simply targeting individuals living in earthquake-affected areas.