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Many mud volcanoes are distributed along the tectonic sutures in southern Taiwan and can be divided into five zones based on their relative positions in different tectonic domains. Most active mud volcanoes are exhaling methane-dominated gases. Nevertheless, some gases show unusual carbon dioxide-dominated and/or nitrogen-excess compositions. This implies that there are multiple sources for the gas compositions of mud volcanoes in Taiwan. For better understanding the total amount of exhalation gases and its flux, the gas flow and compositions were continuously measured in the interval of two minutes at Chung-lun (CL) bubbling mud pool for a few months. The major compositions of gases exhaling from this site were 75$90% of CO 2 and 5$12% of CH 4 . The amount of gases exhaling from the mud pool can be estimated to be about 1.4 ton/year for CH 4 and 28 ton/year for CO 2 , respectively. The preliminary results of exhaling gas flux from the major vents of representative active mud volcanoes, yielded an estimated total CH 4 output of the mud volcanoes in Taiwan of ca. 29 ton/year during quiescent period.

The 21 September 1999 Chi-Chi earthquake (M w 7.6) occurred on eastdipping shallow thrust faults that produced a high-relief surface rupture. Extraordinary surface breaks appeared that could be clearly traced for about 100 km across many counties. These thrust faults, the Chelungpu and Shihkang, are part of an active fold-and-thrust belt related to ongoing recent arc-continent collision. Measurement of slip vectors along the earthquake rupture indicates that the orientation of the maximum shear stress changed from a westward direction (N70-90ЊW) on the Chelungpu fault to a northwestward direction (N30-40ЊW) on the Shihkang fault. The stress field underwent a clockwise rotation of about 40Њ during the Chi-Chi earthquake. Near-rupture vertical displacements in the hanging wall of the Shihkang fault have more cumulative displacement than on the Chelungpu fault, which is consistent with Global Positioning System (GPS) measurements. Maximum vertical offset on the rupture was found to be about 10 m by the surficial rupture and GPS measurements. In addition, analysis of crustal deformation by GPS measurements on the hanging wall defines a coseismic uplift related to a fault ramp structure. Our synthesis of geological and geodetic analyses shows the importance of ramp structures associated with thrust faults for generating large earthquakes and provides a general framework for understanding earthquake in fold-and-thrust belts. Large surficial coseismic uplift and strong asperities appear to be a function of fault ramp geometry. Our analysis also indicates that, in general, ramp structures in fold-andthrust belts may have a high potential in generating large earthquakes.

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The spatial variation of the fractal dimension and its geologic implica tions are studied using an empirical approach. The fractal parameters, including the surface's fractal dimension, D .. the angular fractal dimensur[� sion, D , the gamma ( y) value and the break-distance (R), are derived by ang the variogram method. Synthetic surfaces are generated by the successive random addition (SRA) method by assigning different values to the Hurst exponent. Two test sites were selected to study the link between the fractal parameters and the geologic features. The following conclusions can be drawn from this research: (1) The fractal parameters of a landscape sur face are region-dependent and scale-dependent. The spatial distribution of fractal parameters should be studied in a suitable size of spatial unit. (2) The angled variogram method can readily disclose the anisotropic nature of a landscape surface. (3) The surface's fractal dimension reflects the litho logic variations underlying a landscape surface, and the gamma value re flects the topographic relief of the surface. (4) The mean direction and the vector resultant of angular fractal dimensions have a close relation with the major geological structures of the landscape.