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In summer 1995, in collaboration with the deep multi-channel seismic profiling project around the island of Taiwan, an onshore-offshore wide angle deep seismic profiling experiment was conducted in Taiwan. The re sults are expected to provide the first complete seismic images of the deep crustal structure for a better understanding of the Taiwan orogeny and subduction-collision system. The experiment consists of three profiles, one along each of the central and southern cross-island highways and another on the south-link highway of the island. For the first two lines, 35 three component portable seismographs were deployed along each of the 116 and 135 km-long profiles onshore, with airgun shots being fired at distances

Wide-angle reflection and refraction data are used to illustrate the crustal structures in the central Taiwan area, across the Taiwan Orogen and in the westernmost part of the Ryukyu subduction system. The pre liminary structures were derived by modeling the data set collected using onshore seismic recording instruments along the central cross-island high way in 1995. Seismic signals were generated by the powerful airgun arrays of the RIV Ewing in the seas east of Taiwan. For the shallow structures, results from the forward modeling of the Pg phases show that strong lat eral variations of P-wave velocities in the upper crust were obtained. Ve locities at the uppermost crust have a wide range from 3.0 km/sec to 5.2 km/sec, and increase from 5.8 km/sec to 6.8 km/sec at the bottom of the upper crust. The thickness of the upper crust increases from 22 km be neath the Western Central Range to 25 km beneath the Hsincheng Ridge, and it then dramatically decrease to only 10 km beneath the Hoping and Nanao basins. For the deep crust structures, similar pattern of thickness variations, from 12 km to 20 km, was obtained. Velocities at the lower crust range from 6.4 -6.7 km/sec at its top to 7.2 -7.3 km/sec at its bottom. In summary, the crustal thickness beneath the island could be over 40 km, but only about 25 km beneath the westernmost part of the Ryukyu forearc re gion. The thickest crust is not right beneath the highest mountains on the island but with an offset of about 40 km toward the east. The result indi cates that Taiwan has still not yet reached to its isostatic equilibrium yet.

The 21 September 1999 earthquake (M W 7.6) produced a surface rupture that extended for 100-km in a general north-south direction in front of the Western Foothills, central Taiwan. The study area, located in a segment of the fold -thrust belt of central Taiwan, provides an important natural laboratory to study the relationship between active thrust deformation and fluvial terrace development. We recognize, from west to east, three subparallel thrusts, the Sanyi, Houli, and Shihkang faults in the northern part of the earthquake disaster area. The 1999 earthquake rupture occurred only along the Shihkang fault, whereas the other two faults were inactive. Along the Tachia River in the hanging wall of the Shihkang fault, eight well-developed terrace levels are observed, and can be subdivided into lateritic (Lt5-Lt1) and non-lateritic terraces (Ft3 -Ft1). Five levels of lateritic terrace (Lt5 -Lt1) are located in the hanging wall of the Houli fault, and a lateritic terrace (Lt5) is present in the hanging wall of the Sanyi fault. Stratigraphic and elevation correlations between these well-developed fluvial terraces in relationship to nearby geologic structures show that the Sanyi fault is the oldest structure. Lateritic terraces of at least 10,000 yr BP, for example, overlie the Sanyi fault, but correlative terraces associated with the Houli fault are offset. These types of terrace correlations allow us to define the progressive development of the thrust system within the Western Foothills. q

Microbial fuel cells (MFCs) represent a novel technology for wastewater treatment with electricity production. Electricity generation with simultaneous nitrate reduction in a single-chamber MFC without air cathode was studied, using glucose (1 mM) as the carbon source and nitrate (1 mM) as the final electron acceptor employed by Bacillus subtilis under anaerobic conditions. Increasing current as a function of decreased nitrate concentration and an increase in biomass were observed with a maximum current of 0.4 mA obtained at an external resistance ( R ext ) of 1 KΩ without a platinum catalyst of air cathode. A decreased current with complete nitrate reduction, with further recovery of the current immediately after nitrate addition, indicated the dependence of B. subtilis on nitrate as an electron acceptor to efficiently produce electricity. A power density of 0.0019 mW/cm 2 was achieved at an R ext of 220 Ω. Cyclic voltammograms (CV) showed direct electron transfer with the involvement of mediators in the MFC. The low coulombic efficiency (CE) of 11% was mainly attributed to glucose fermentation. These results demonstrated that electricity generation is possible from wastewater containing nitrate, and this represents an alternative technology for the cost-effective and environmentally benign treatment of wastewater.

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We present a layer-stripping method of migration for irregularly layered media in which first-order velocity discontinuities separate regions of constant or smoothly varying velocity. We use the reverse-time method to migrate seismic data layer by layer, from the surface downwards. As part of the migration of a given layer, the bottom boundary of the layer is defined based on power in the migrated signal, and a seismic section is collected along it. This new section serves as the boundary condition for migration in the next layer. This procedure is repeated for each layer, with the final image formed from the individual layer images. Layer-stripping migration consists of three steps : (1) layer definition, (2) wavefield extrapolation and imaging, and (3) boundary determination. T h e migration scheme when used with reverse-time extrapolation is similar to datuming with an imaging condition. The reverse-time method uses an explicit fourth-order time, tenth-order space, finite-difference approximation to the scalar wave equation.The advantages of layer-stripping reverse-time migration are : (1) it preserves the benefits of the reverse-time method by handling strong velocity contrasts between layers and steeply dipping structures; (2) it reduces computer memory and saves computation time in high-velocity layers, and (3) it allows interpretational control of the image.Post-stack layer-stripping reverse-time migration is illustrated with a synthetic CMP data example. Prestack migration is illustrated with a synthetic data set and with a marine seismic reflection profile across the Santa Maria Basin and the Hosgri Fault in central California.

Abstract. Various types of damage caused by the devastating 1999 Chi-Chi, Taiwan earthquake were not only experienced in the hanging wall and footwall but also in the southern and northern parts of the Chelungpu fault. In this paper, we determine the coseismic displacements and determine stress relaxation using a rupture model and compare the values with surface damage. The patterns of damage can be clearly correlated with the calculated coseismic displacement and stress relaxation caused by the event. It is found that the surface damage was predominately caused by coseismic deformation and that large-scale landslides were mainly a result of steep coseismic displacements.