J. Bruce H. Shyu - Academia.edu (original) (raw)

Papers by J. Bruce H. Shyu

Journal of Asian Earth Sciences, 2014

ABSTRACT On July 22, 2013, an earthquake of Ms. 6.6 occurred at the junction area of Minxian and ... more ABSTRACT On July 22, 2013, an earthquake of Ms. 6.6 occurred at the junction area of Minxian and Zhangxian counties, Gansu Province, China. This earthquake triggered many landslides of various types, dominated by small-scale soil falls, slides, and topples on loess scarps. There were also a few deep-seated landslides, large-scale soil avalanches, and fissure-developing slopes. In this paper, an inventory of landslides triggered by this event is prepared based on field investigations and visual interpretation of high-resolution satellite images. The spatial distribution of the landslides is then analyzed. The inventory indicates that at least 2330 landslides were triggered by the earthquake. A correlation statistics of the landslides with topographic, geologic, and earthquake factors is performed based on the GIS platform. The results show that the largest number of landslides and the highest landslide density are at 2400 m–2600 m of absolute elevation, and 200 m–300 m of relative elevation, respectively. The landslide density does not always increase with slope gradient as previously suggested. The slopes most prone to landslides are in S, SW, W, and NW directions. Concave slopes register higher landslide density and larger number of landslides than convex slopes. The largest number of landslides occurs on topographic position with middle slopes, whereas the highest landslide density corresponds to valleys and lower slopes. The underlying bedrocks consisting of conglomerate and sandstone of Lower Paleogene (Eb) register both the largest number and area of landslides and the highest landslide number and area density values. Correlations of landslide number and landslide density with perpendicular- and along-strike distance from the epicenter show an obvious spatial intensifying character of the co-seismic landslides. The spatial pattern of the co-seismic landslides is strongly controlled by a branch of the Lintan-Dangchang fault, which indicates the effect of seismogenic fault on co-seismic landslides. In addition, the area affected by landslides related to the earthquake is compared to the relationship of “area affected by landslides vs. earthquake magnitude” constructed based on earthquakes worldwide, and it is shown that the area affected by landslides triggered by the Minxian–Zhangxian earthquake is larger than that of almost all other events with similar magnitudes.

The tectonic activity of the Taiwan orogenic belt has been well studied by different methods in v... more The tectonic activity of the Taiwan orogenic belt has been well studied by different methods in various time scales, such as long-term (>1 Ma) thermochronologic data and short-term (yearly to decadal) geodetic analysis. However, constrains on millennial-scale tectonic characteristics is limited, especially in the mountainous core of the island. Recent studies show the channel networks in active orogens reflect the pace at which landscapes respond to tectonic processes and provides a record of relative changes in rock uplift. Therefore, we attempted to use river steepness index (ksn) derived from the stream power incision model, combined with knick point distributions from bedrock rivers to obtain the signature of tectonic forcing spatially and temporally. We analyzed 21 rivers along the eastern flank of the Central Range, Taiwan. We chose the main trunk of each river system as the major branch flowing from the ridgeline of the Central Range and perpendicular to the main structure...

The central Andes in South America is formed as the Nazca plate subducts northeastward beneath th... more The central Andes in South America is formed as the Nazca plate subducts northeastward beneath the South American plate along the Peru-Chile trench, parallel to the coastline. It has been shown that the convergence rate between the two plates is ~70-80 mm/yr, and about 10-15 mm/yr of the convergence is absorbed in the sub-Andean belt, east of the active volcanic arc. However, the convergence in the forearc region is still not well constrained. In order to understand how much convergence is absorbed in the forearc region, we analyzed the active tectonic characteristics of the Atacama Basin, just west of the active volcanic arc. With the help of various remote sensing datasets such as 30-m and 90-m resolution digital elevation models (DEM) produced from SRTM data, thermal infrared radiometer (TIR) ASTER images, Landsat, and Google Earth images, we identified many N-S trending compressional structures around the Atacama Basin. The active structures are found mainly in the northern and ...

Journal of Geophysical Research: Solid Earth, 2014

ABSTRACT [1] We used aerial photos taken before and after the September 21, 1999, Mw 7.6, Chi-Chi... more ABSTRACT [1] We used aerial photos taken before and after the September 21, 1999, Mw 7.6, Chi-Chi earthquake in central Taiwan to measure the near-field ground deformation. A total of 12 pairs of images were processed with COSI-Corr to produce a horizontal displacement map of a 10 km x10 km area near Tsaotun. Using pairs of images with different viewing angles, both the horizontal and vertical slip across the fault zone can be measured. Our measurements when resampled into lower resolution are consistent with lower resolution measurements of horizontal displacements obtained from SPOT images, as well as with vertical displacements obtained from repeated leveling measurements and field observations. Horizontal strain is strongly localized along the Chelungpu fault (CLPF) and along a secondary scarp that runs parallel to the CLPF about 2 km to the East, the Ailiao fold scarp (ALF). This pattern closely matches the surface ruptures mapped in the field. Horizontal strain across CLPF correlates remarkably well with the topographic features produced by long-term deformation. The cumulative horizontal shortening across the CLPF and ALF amounts to 4.9 ± 0.4 and 6.1 ± 0.6 m, respectively, and fault-parallel displacement is 3.4 ± 0.4 m. The pattern of surface strain is consistent with the interpretation of the ALF as a fold scarp formed over an active axial hinge zone. This study shows that, even in this compressional setting, most surface deformation is localized within narrow fault zones or active axial hinges.

The Longitudinal Valley (LV) is one of the major geologic sutures within collision zone of Taiwan... more The Longitudinal Valley (LV) is one of the major geologic sutures within collision zone of Taiwan, in which the Costal Range Fault (CRF) is the most active fault located in its eastern margin. The main goal of this study is to diagnose the geometry and behavior of ...

Journal of Geophysical Research, 2006

Journal of Geophysical Research, 2005

1] The disastrous effects of the 1999 Chi-Chi earthquake in Taiwan demonstrated an urgent need fo... more 1] 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.

Journal of Asian Earth Sciences, 2011

A very common but important observation of collided and accreted volcanic arcs is that the forear... more A very common but important observation of collided and accreted volcanic arcs is that the forearc regions of these arcs are largely or even entirely missing. The processes and mechanisms responsible for the removal and transport of the forearc materials from the collisional belts are thus important issues in understanding tectonics and crustal growth. The young and ongoing collision between

Journal of Asian Earth Sciences, 2007

The earthquakes of November 1951 constitute the most destructive seismic episode in the recorded ... more The earthquakes of November 1951 constitute the most destructive seismic episode in the recorded history of the Longitudinal Valley, eastern Taiwan. However, information about their source parameters is sparse. To understand the relationship between the 1951 ruptures and the new interpretations of the regional neotectonic architecture of the Longitudinal Valley, we re-evaluated the November 1951 ruptures by analyzing old documents, reports and photographs, and by interviewing local residents who experienced the earthquake. As a result, we have revised significantly the rupture map previously published. We divide the surface ruptures into Chihshang, Yuli, and Rueisuei sections. The first shock of the 1951 series probably resulted from the Chihshang rupture, and the second shock probably resulted from the Yuli and Rueisuei ruptures. The lengths of these ruptures indicate that the two shocks had similar magnitudes. The Chihshang and Rueisuei ruptures are along segments of the Longitudinal Valley fault, a left-lateral oblique fault along which the Coastal Range thrusts westward over the Longitudinal Valley. The Yuli rupture, on the other hand, appears to be part of a separate, left-lateral strike-slip Yuli fault, which traverses the middle of the Longitudinal Valley. The complex behavior of these structures and interaction between them are important in understanding the future seismic hazard of the area.

Geomorphology, 2012

With cumulative rainfall of 1700 mm, Typhoon Morakot triggered a catastrophic landslide at Hsiao-... more With cumulative rainfall of 1700 mm, Typhoon Morakot triggered a catastrophic landslide at Hsiao-lin (9 August, 2009), which dammed the river, buried the village and killed> 400 people. We conducted a geomorphic study to understand the origin of this landslide in the context of the long-term evolution of the hillslope. The landslide originated from a broad, poorly drained slope (21°-23°) and ran down along two first-order channels. The erosion, up to 80 m thick, has created a concave-shape slope and exposed mostly loose debris, which implies that the landslide was mainly the reworking of ancient colluviums. The genesis of the concave-shape slope where the source sediments of the landslide resided reflects the weakness of the mudstone/shale bedrock underlying this slope, in contrast to the sandstone-based transport area. The two channels in the transport area also follow old faults or joints. Given that the source area has been subject to erosion during large landslides, the subsequent deposition here was likely achieved by minor colluvial processes. This deposition continued until the catastrophic failure in 2009, which could be controlled by (1) the amount of sediments deposited, which determined the slope angle, and (2) the headward expansion of the channels from the transport area, which enhanced groundwater convergence and later provided routes for the landslide materials to run downslope. Extensive mass-wasting motions had occurred in the area, as shown by the prevalence of >20 m thick landslide/ debris-flow sequences on the lower part of the hillslope, which are dated 21, 14.9, 13.7 and 12.0 ka by the radiocarbon method. These mass-wasting events had hindered the long-term incision of the trunk river in response to the rapid tectonic uplift. At least the 12.0 ka event, which caused extensive mud-flow deposition, had dammed the river. Overall, this study shows how bedrock lithology and structures controlled the shape of a hillslope and caused extremely unsteady mass-wasting transport in the active mountains of Taiwan.

Earth and Planetary Science Letters, 2005

Taiwan's numerous active faults and folds demarcate distinct eastern and western neotectonic belt... more Taiwan's numerous active faults and folds demarcate distinct eastern and western neotectonic belts. The western belt results from the attachment and subsequent detachment of a sliver of continental lithosphere to the Eurasian continental margin. The eastern belt is the product of the same continental sliver docking with and then separating from the Luzon volcanic arc. Thus, the active Taiwan orogen is a tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the Eurasian continental margin. This progressive suturing and separation is a superb, living demonstration of the fundamental weakness of lithospheric sutures. Furthermore, this neotectonic architecture provides the basis for understanding the Taiwan's seismic sources. D

A B S T R A C T The fault systems of Taiwan have been repeatedly studied over many decades. Still... more A B S T R A C T The fault systems of Taiwan have been repeatedly studied over many decades. Still, new surveys consistently bring fresh insights into their mechanisms, activity and geological characteristics. The neotectonic map of Taiwan is under constant development. Although the most active areas manifest at the on-land boundary of the Philippine Sea Plate and Eurasia (a suture zone known as the Longitudinal Valley), and at the southwestern area of the Western Foothills, the fault systems affect the entire island. The Hengchun Peninsula represents the most recently emerged part of the Taiwan orogen. This narrow 20–25 km peninsula appears relatively aseismic. However, at the western flank the peninsula manifests tectonic activity along the Hengchun Fault. In this study, we surveyed the tectonic characteristics of the Hengchun Fault. Based on fieldwork, four years of monitoring fault displacement in conjunction with levelling data, core analysis, UAV surveys and mapping, we have re-evaluated the fault mechanisms as well as the geological formations of the hanging and footwall. We surveyed features that allowed us to modify the existing model of the fault in two ways: 1) correcting the location of the fault line in the southern area of the peninsula by moving it westwards about 800 m; 2) defining the lithostratigraphy of the hanging and footwall of the fault. A bathymetric map of the southern area of the Hengchun Peninsula obtained from the Atomic Energy Council that extends the fault trace offshore to the south distinctively matches our proposed fault line. These insights, coupled with crust-scale tomographic data from across the Manila accretionary system, form the basis of our opinion that the Hengchun Fault may play a major role in the tectonic evolution of the southern part of the Taiwan orogen.