Changhua Fault Research Articles

Evaluating the Seismic Hazards by Chang-Hua Fault at Nantou County, Taiwan and Disaster Resistant Strategy

Because of geology and complex seismic source mechanisms, Taiwan suffers attacks of earthquake calamity. In this research, we investigate the seismic hazards caused by Changhua fault and focus on the hazards at Nantou County, Taiwan. The PGA and spectral intensities, SIs, including acceleration, velocity, and displacement (SIa, SIv, and SId), are employed to estimate potential damages. The maximum seismic intensity will occur at Ming-Chien town and the buildings at Caotun Township and Nantou city will be destroyed seriously. The part of freeway 3 which connects Caotun Township and Nantou city has to be paid more attentions to prevent the destructive fractures. Based on the predicted seismic hazards, the best way to reduce the losses of lives and properties of people is preparing a well-rounded mitigation plan in advance. When an earthquake occurs abruptly, a community-based approach to establish an excellent self-aid and mutual-aid system is an efficient method for reducing the casualties. It requires a community-wide effort over a long period of time for making the community comfortable and safe. A detailed process of a community-based mitigation plan for the seismic hazards is discussed in the paper.

Spatial variation of seismogenic depths of crustal earthquakes in the Taiwan region: Implications for seismic hazard assessment

This paper presents the first whole Taiwan-scale spatial variation of the seismogenic zone using a high-quality crustal seismicity catalog. The seismicity onset and cutoff depths (i.e., seismogenic depths) are determined by the earthquake depth–moment distribution and used to define the upper and lower boundaries of the seismogenic zone, respectively. Together with the published fault geometries and fault area–moment magnitude relations, the depth difference in the onset and cutoff depths (i.e., seismogenic thickness) is used as the fault width to determine the moment magnitudes of potential earthquakes for the major seismogenic faults. Results show that the largest (Mw7.9–8.0) potential earthquake may occur along the Changhua fault in western Taiwan, where the seismic risk is relatively high and seismic hazard mitigation should be a matter of urgent concern. In addition, the first-motion focal mechanism catalog is used to examine the relation between the seismogenic depths and earthquake source parameters. For crustal earthquakes (≤50km), the shallowest onset and cutoff depths are observed for normal and strike-slip events, respectively. This observation is different from the prediction of the conventional continental-rheology model, which states that thrust events have the shallowest cutoff depth. Thus, a more sophisticated rheology model is necessary to explain our observed dependence of the seismogenic depths on faulting types. Meanwhile, for intermediate to large crustal (Mw≥4; depth≤50km) earthquakes, thrust events tend to occur at the bottom region of the seismogenic zone, but normal and strike-slip events distribute at a large depth range.

Estimation of seismic hazard potential in Taiwan based on ShakeMaps

A catalog of 2,044 shallow earthquakes occurring from 1900 to 2010 with Mw magnitudes ranging from 5.0 to 8.2 and 11 disastrous earthquakes occurring from 1683 to 1899 are used to estimate the seismic hazard potential in Taiwan using ShakeMaps. The ShakeMaps show that a high Modified Mercalli Intensity (MMI) greater than VIII in the Taipei basin, Nanao, Ilan plain, Chianan plains, Hualien and Taitung Longitudinal Valley is all related to the large damaging earthquakes occurring in these areas. Relatively low seismic hazard potential in Changhua area with a peak ground acceleration lower than 200 gal based on data from 1900 to 2010 may be misleading, considering the occurrence of damaging historical earthquakes before 1900 and the presence of Changhua fault in the area. In addition, based on seismic intensity probabilities for the 16 selected major cities in Taiwan over 10-, 30- and 50-year periods corresponding to a MMI greater than VI, VII and VIII, the results indicate that Chiayi, Yunlin, Ilan and Hualien have the highest possibilities of shaking hazards, while Taipei, New Taipei and Taoyuan have lower possibilities, and Kaohsiung and Pingtung have the lowest. Specifically, for the largest cities, Taipei and New Taipei, the probabilities of experiencing moderate damaging earthquake shaking within a 10-year period are 13 and 24 %, respectively.

Comment on “Annual probability and return period of soil liquefaction in Yuanlin, Taiwan attributed to Chelungpu Fault and Changhua Fault” by Lee et al., in Engineering Geology, 114: 343–353 (2010)

This note provides the overview of the calculation in soil liquefaction probability in Central Taiwan carried out by Lee et al. Although that estimation is by all means original and offers an in-depth evaluation on the liquefaction risk for Central Taiwan, we raised a few questions about its earthquake magnitude function, source-to-site distance function, and the fault distributions in Central Taiwan. We personally think that with those concerns being accounted for, that estimation should be more robust.

Reply to comments by JP Wang and Duruo Huang on “Annual probability and return period of soil liquefaction in Yuanlin, Taiwan attributed to Chelungpu Fault and Changhua Fault” by Lee et al. (2010) in Engineering Geology, 114: 343–353

0013-7952/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2012.05.002 where v is the average rate of threshold magnitude exceedance. As implied in Equation (3) of the paper, the threshold magnitude and v are set to:m0=4 and v=1, which means the earthquake with a magnitude of at least 4 occur once in every year. In general, the authors agree that inclusion of the v term in the formulation makes it a more complete equation. Nevertheless, the assumption of m0=4 and v=1 is quite reasonable in Taiwan. While the Chelungpu Fault induced only six catastrophic events in the past two thousand years, smaller earthquakes were typically not reported. If all earthquakes with a magnitude of at least 4 were reported and accounted for, which occurred quite frequently, the number of events would drastically increase. A conservative assumption of v=1 for estimation of the annual liquefaction probability in central Taiwan is considered quite reasonable in this case.

Annual probability and return period of soil liquefaction in Yuanlin, Taiwan attributed to Chelungpu Fault and Changhua Fault

In this paper the results of a case study of the annual probability and return period of soil liquefaction in Yuanlin, Taiwan, the town that suffered significant liquefaction damage in the 1999 Chi-Chi earthquake, are presented. As part of this case study, a framework for determining the average annual probability of liquefaction ( AAPL) that is attributed to a known fault is developed. This framework is formulated by considering the uncertainties in both liquefaction resistance and liquefaction loading. For liquefaction loading, the seismic hazard from a known fault is considered; and for liquefaction resistance, soil parameters, characterized mainly by cone penetration test (CPT) and standard penetration test (SPT), and their uncertainties are considered. Additionally, model uncertainty of the empirically-developed liquefaction resistance models, based either on CPT or SPT, is considered in the analysis for the annual liquefaction probabilities. The results of the case study show that the proposed framework is applicable for site-specific analysis of liquefaction potential or for mapping liquefaction potential in a given town (or city). Furthermore, the AAPL and return period determined based on SPTs are found to be comparable with those determined with CPTs. The results of the case study provide some guidance for future engineering planning and regulation consideration in the Yuanlin, Taiwan area.

High-resolution sequence stratigraphic analysis of Late Quaternary deposits of the Changhua Coastal Plain in the frontal arc-continent collision belt of Central Taiwan

Detailed analysis of the sequence stratigraphy in 30 cores from the Late Quaternary deposits of the Changhua Coastal Plain provides a 25 ka record of the depositional history of a region situated in the frontal arc-continent collision belt of Taiwan. Twenty-five lithofacies and nine facies associations are recognized. An alluvial plain was the dominant feature during a pronounced sea-level fall at 25–20 ka ago. Between 20 and 10 ka, alluvial fans were deposited along the western front of the Pakua Tableland during movement along the Changhua Fault, and a local sag basin was produced. No other deposits in the seaward area are recognized between 20 and 16 ka, or in the landward area between 20 and 10 ka. Between 16 and 6 ka, the Changhua Coastal Plain experienced rising sea level and retrogradational deposition. From 16 to 10 ka, estuarine deposits (lower transgressive systems tract) were deposited, and the base of these deposits defines the Last Glacial Maximum (LGM) unconformity (sequence boundary), now preserved in four regions to the east of the plain. From 10 to 6 ka, shelf, shoreface, and lagoonal deposits (upper transgressive systems tract) were laid either on top of the estuarine deposits or directly on the LGM unconformity surface. By about 7–6 ka, sea level had reached its peak (maximum flooding surface), and shelf and marginal marine sediments covered most of the study area. After 6 ka, the highstand was dominated by progradation of offshore-transition, shoreface, lagoonal, tidal channel, tidal flat and alluvial plain deposits. One-thousand-year-old fluvial deposits in incised channels are preserved in the central part of the Changhua Coastal Plain. Since then, fluvial channels shifted southward to the present-day Chuoshuei River. The depositional patterns in this tectonically active area during the last interglacial period reflect the complex interplay between high-frequency sea-level fluctuations, tectonics (subsidence and uplift), and autocyclic processes. In the seaward area, however, fluctuations in sea level were clearly the dominant factor in controlling the nature of depositional facies.

River terrace development in response to folding above active wedge thrusts in Houli, Central Taiwan

Folding at the leading edge of the western Taiwan thrust belt is well preserved by a flight of fluvial terraces at Houli. Strain in this region is driven by slip on the north trending Changhua and Sanyi blind wedge thrusts and occurs at the boundary between the Miaoli and Taichung neotectonic domains located respectively to the north and south. In the past century, two large historical earthquakes occurred in these two domains and produced surface ruptures within or close to the study area, indicating Houli is not only tectonically active but also critical for understanding the interaction between the neighboring active systems. Although abundant river terraces and their deformation by active structures have long been well known in the area, a kinematical model for this region has not yet been proposed. We have therefore remapped the geomorphic features using the 40 m DEM and aerial photos to identify often subtle structural features in order to separate the effects of folding interference produced by different active structural systems. Besides the Tuntzuchiao fault (TTCF), which generated the 1935 earthquake, two other active regional scale structural systems have been reported in Houli area: the Tiechanshan (TCS) anticline and the Changhua fault (CHF). Our results demonstrate a number of tectonic scarps and warped surfaces in association with the CHF and its coupled back thrust, indicating that the CHF system is active. In contrast, the flight of fluvial terraces distributed in the middle of the study area cannot be related to the growth of the TCS anticline. Instead, terraces here record growth of another smaller and previously unknown anticline, Yuehmei (tentatively named in this study and shortened to YM in the text). Although it has developed parallel to the TCS anticline, relevant seismic profiles show the YM anticline as a local drag-fold attached to the southern limb of the TCS anticline and restricted in the Houli area. Based on the above observation, the TCS anticline can be interpreted as becoming less active where strain is instead transferred to the more rapidly uplifting YM anticline. This structural switch may be the result of interference between the newly developed southern Taichung system and the preexisting TCS anticline.

Pedogenic approach to resolving the geomorphic evolution of the Pakua river terraces in central Taiwan

The southern part of the Pakua tableland in Taiwan comprises a series of wide, unpaired river terraces that have as many as six altitude levels, from PK-1 (highest) to PK-6 (lowest). The terrace surfaces are covered with lateritic soils. This study described, sampled and analyzed the soils from each terrace. Soil taxonomies are Oxisol, Ultisol and Inceptisol . Soil morphological characteristics were quantified as a profile development index (PDI) to determine the degree of soil development. The chemical analyses included cation exchange capacity (CEC) and selected extraction of Fe in soils. Based on the degree of soil development, surface deposits on terrace flights form the post-incisive soil chronosequence, supporting the hypothesis of terrace formation by fluvial processes. Soil ages were estimated based on iron crystallinity (Fe d–Fe o)/Fe t. Analytical results indicate that river terraces in the Pakua tableland are aged 40–400 ka. The long-term uplift rate of the tableland can be estimated using terrace ages and folding geometry. The variation of uplift rates demonstrates that the landscape underwent increased shortening of frontal thrusting by the Changhua Fault running beneath the tableland.

Neotectonic architecture of Taiwan and its implications for future large earthquakes

The disastrous effects of the 1999 Chi‐Chi earthquake in Taiwan demonstrated an urgent need for better knowledge of the island's potential earthquake sources. Toward this end, we have prepared a neotectonic map of Taiwan. The map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40‐m resolution digital elevation model, augmented by geodetic and seismologic data. The active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the Eurasian continental margin have created two neotectonic belts in Taiwan. In the southern part of the orogen both belts are in the final stage of consuming oceanic crust. Collision and suturing occur in the middle part of both belts, and postcollisional collapse and extension dominate the island's northern and northeastern flanks. Both belts consist of several distinct neotectonic domains. Seven domains (Kaoping, Chiayi, Taichung, Miaoli, Hsinchu, Ilan, and Taipei) constitute the western belt, and four domains (Lutao‐Lanyu, Taitung, Hualien, and Ryukyu) make up the eastern belt. Each domain is defined by a distinct suite of active structures. For example, the Chelungpu fault (source of the 1999 earthquake) and its western neighbor, the Changhua fault, are the principal components of the Taichung Domain, whereas both its neighboring domains, the Chiayi and Miaoli Domains, are dominated by major blind faults. In most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid‐7 values.

Surface Rupture of 1999 Chi-Chi Earthquake Yields Insights on Active Tectonics of Central Taiwan

The 1999 Chi-Chi earthquake was caused by rupture of the Chelungpu fault, one of the most prominent active thrust faults of Taiwan. This largest of Taiwan's historical fault ruptures broke the surface for over 90 km at the western base of the rugged mountain range. A short right-lateral tear extended southwestward from the southern end of the Chelungpu fault, and a complex assemblage of shallow folds and faults ran northeastward from the northern end. Vertical offsets averaged about 2 m along the southern half of the Chelungpu fault and about 4 m along the northern half, and offsets of 5 to 7 m were typical along the northern part of the major thrust. The sinuous nature of the surface trace is consistent with seismographic data that indicate a dip of about 30°. The 1999 rupture draws attention to the fact that this active fault system is highly segmented and that this segmentation influences the characteristics of seismic ruptures. Active faults to the south, north, and west of the Chelungpu fault have distinctly different characteristics. Faults to the south and north broke the surface during earthquakes in 1906 and 1935. The active Changhua fault to the west, a blind thrust similar in length to the Chelungpu, has not ruptured in the historical period and should be considered a prime candidate for generating a future earthquake. Manuscript received 4 October 2000.

Why does the co-seismic slip of the 1999 Chi-Chi (Taiwan) earthquake increase progressively northwestward on the plane of rupture?

The Chi-Chi 1999 earthquake ruptured the out-of-sequence Chelungpu Thrust Fault (CTF) in the fold-and-thrust belt in Western Central Taiwan. An important feature of this rupture is that the calculated slip increases approximately linearly in the SE–NW convergence plate direction from very little at its deeper edge to a maximum near the surface. We propose here a new explanation for this co-seismic slip distribution based on the study of both stress and displacement over the long-term as well as over a seismic cycle. Over the last 0.5 My, the convergence rate in the mountain front belt is accommodated by the frontal Changhua Fault (Ch.F), the CTF and the Shuangtung Fault (Sh.F). Based on previously published balanced cross sections, we estimate that the long-term slip of the Ch.F and of the CTF accommodate 5–30% and 30–55% of the convergence rate, respectively. This long-term partitioning of the convergence rate and the modeling of inter-seismic and post-seismic displacements suggest that the peculiar linear co-seismic slip distribution is accounted for by a combination of the effect of the obliquity of the CTF to the direction of inter-seismic loading, and of increasing aseismic creep on the deeper part of the Ch.F and CTF. Many previous interpretations of this slip distribution have been done including the effects of material properties, lubrication, site effect, fault geometry and dynamic waves. The importance of these processes with respect to the effects proposed here is still unknown. Taking into account the dip angle of the CTF, asperity dynamic models have been proposed to explain the general features of co-seismic slip distribution. In particular, recent works show the importance of heterogeneous spatial distribution of stress prior to the Chi-Chi earthquake. Our analysis of seismicity shows that previous large historic earthquakes cannot explain the amplitude of this heterogeneity. Based on our approach, we rather think that the high stress in the northern part of the CTF proposed by Oglesby and Day [Oglesby, D.D., Day, S.M., 2001. Fault geometry and the dynamics of the 1999 Chi-Chi (Taiwan) earthquake. Bull. Seismol. Soc. Am. 91, 1099–1111] reflects the latitudinal variation of inter-seismic coupling due to the obliquity of the CTF.

Coseismic displacements of the footwall of the Chelungpu fault caused by the 1999, Taiwan, Chi-Chi earthquake from InSAR and GPS data

The differential SAR interferometry technique (interferometric synthetic aperture radar, InSAR) is applied on the Chelungpu fault surface rupture zone of the September 20, 1999, Taiwan, Chi-Chi earthquake using six ERS-2 images covering the period from February 1999 to January 2000. As compared with available geodetic data, InSAR measurements result in more extensive analysis because of high spatial sampling and centimetric accuracy. However, coseismic displacements can be evaluated only on the footwall of the fault. The analysis of interferograms shows the existence of a linear trend in phase difference mainly caused by orbital errors, which we removed from interferograms using GPS data. The corrected interferograms provide a precise map of the InSAR component of the coseismic displacement, showing a continuous decrease over the footwall from a maximum of 36.7 cm at the fault east of Taichung city to a value of about 5 cm at the coastline 30 km further west. The map analysis reveals that the Changhua fault (whose surface trace is located about 20 km west of the Chelungpu one) and the Tuntzuchio fault influence the displacement field. We interpret this in terms of minor reactivation of these faults triggered by the earthquake. A 1.7 cm uncertainty, estimated from the GPS data, is proposed to quantify the precision of the map. Beyond this single value, we highlight the interest of having several coseismic interferograms to evaluate the reliability of the map in a more comprehensive way. Comparisons with displacements inferred from models of slip distribution inverted without InSAR data highlight the advantage of carrying out a joint inversion including our results as new constraints.

Investigating Near-surface Structures under the Changhua Fault, West-central Taiwan by the Reflection Seismic Method

The Changhua fault is a long fault (80 km), extending along the western border of three gravel terraces in west-central Taiwan. It represents the western-most thrust fault in the deformation front of Taiwan’s western foothill area. Photogeologic studies indicate that it could be an active fault, as it has apparent lineation and fault scarps. In this study, we used the shallow reflection seismic method to map the near-surface structures around the fault and to examine its activity level. It is surprising to find that most of the seismic sections are composed of flat or slant layers and do not show significant traces of fault offsets. Combined with CPC data, we may categorize the fault as a ‘blind-thrust’ buried at the depth of 3 km. Moreover, this long fault can be divided into northern and southern parts most likely separated by a hidden fault: the Tai-an fault. According to the layer bending attitude, the southern part of the Changhua fault (the Pakua terrace area) could be more active, and may still possess a certain degree of reactivity. By contrast, the northern part is relatively flat and quiet with low potential of activity. Besides detecting the Changhua fault, we also inspected its accompanying back-thrust faults: the Tiehchanshan fault and Hengshan fault, finding that they may not exist.

Geomorphic response to growing fault-related folds: example from the foothills of central Taiwan

In this paper we concentrate particularly on the geomorphological indicators left by active tectonics. In the central foothills of Taiwan, we used topography, drainage pattern and structural data to perform quantitative morphometric analysis and to determine relative age of fault-related anticlines. The Tiehchen, Tatu and Pakua ridge belt is a fault-related anticline system located in the hanging wall of the Changhua fault along the western thrust front of the foothills. Geomorphic systems are analysed with intent to detect the various responses of landforms and drainage pattern to late Quaternary deformation. Topography and drainage basin register uplift and are valuable tools to discriminate lateral propagation of an active frontal fold. Geomorphic field evidence and quantitative morphometric parameters are used to define the evolution of the rising anticline ridges and to infer tectonism style along an active front. Geometry of alluvial fans, formed along the frontal side of the anticlines, and weathered terrace deposits provide relevant information on neotectonics. Knowledge concerning these younger anticline ridges, makes this area a good example of an actively forming mountain front. We discuss in detail the origin of N045°, N095 and N120° trending oblique fault scarps which delimite numerous fault blocks. The fault scarps morphology is characterized by imbricate talus facets. Steeper topography accompanied by breaks in the slope along some transverse profiles, seems to correspond to the traces of successive uplifts.

Geomorphic response to growing fault-related folds: example from the foothills of central Taiwan

In this paper we concentrate particularly on the geomorphological indicators left by active tectonics. In the central foothills of Taiwan, we used topography, drainage pattern and structural data to perform quantitative morphometric analysis and to determine relative age of fault-related anticlines. The Tiehchen, Tatu and Pakua ridge belt is a fault-related anticline system located in the hanging wall of the Changhua fault along the western thrust front of the foothills. Geomorphic systems are analysed with intent to detect the various responses of landforms and drainage pattern to late Quaternary deformation. Topography and drainage basin register uplift and are valuable tools to discriminate lateral propagation of an active frontal fold. Geomorphic field evidence and quantitative morphometric parameters are used to define the evolution of the rising anticline ridges and to infer tectonism style along an active front. Geometry of alluvial fans, formed along the frontal side of the anticlines, and weathered terrace deposits provide relevant information on neotectonics. Knowledge concerning these younger anticline ridges, makes this area a good example of an actively forming mountain front. We discuss in detail the origin of N045°, N095 and N120° trending oblique fault scarps which delimite numerous fault blocks. The fault scarps morphology is characterized by imbricate talus facets. Steeper topography accompanied by breaks in the slope along some transverse profiles, seems to correspond to the traces of successive uplifts. © 2001 Éditions scientifiques et médicales Elsevier SAS