[1] This paper investigates the shallow seismicity occurring in the Taiwan region during the 20th century using a stochastic declustering method that has been developed on the basis of the theory of the epidemic-type aftershock sequence model. It provides a probability based tool to objectively separate the space-time occurrences of earthquakes into a background and a clustering component. On the basis of the background and clustering seismicity rates, we discuss the correlation between the distribution of the cluster ratio and the regional seismotectonic structures. Specifically, we find that the areas of the highest clustering ratio correspond to the major strike-slip fault traces in and around Taiwan. Additionally, in the Taiwan inland region, during the period 1960-1990, the outputs for the stochastically declustered catalogue show a clear quiescence in background seismicity preceding the recovery of activation and the occurrences of the 1999 Chi-Chi earthquake of M L 7.3, while the other active regions show stationary background activity. This could be interpreted as an effect of the aseismic slip in the Chi-Chi rupture fault, whereby the inland region around the Chi-Chi source becomes a stress shadow. (2005), A study on the background and clustering seismicity in the Taiwan region by using point process models,

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Juxtaposed against the remnant forearc basin sequences along thrust faults, the Lichi Me ´lange of the Coastal Range of Taiwan is composed of exotic ophiolite and sedimentary blocks, metric to kilometric in size, and coherent turbidite beds, all embedded in a sheared scaly argillaceous matrix. The Lichi Me ´lange is controversial in origin, being interpreted either as a subduction complex, or as an olistostrome. By separating four main deformation levels within the Lichi Me ´lange and adjacent sedimentary rocks, we establish detailed geological maps and structural profiles in two key areas of the Lichi Me ´lange. We reconstruct also the evolution in cross-section and calculate the approximate minimum amount of shortening that corresponds to folding and thrusting in these areas. Our field studies suggest that the Lichi Me ´lange most likely arose from the shearing of lower forearc sequences rather than from a subduction complex or an olistostrome. This conclusion is supported by the structural analysis, the clay mineral distribution, and some interfingering sedimentary relationships between the Lichi Me ´lange and the lower Takangkou Formation. We also undertake a comprehensive tectonic analysis of the shear surfaces in the Lichi Me ´lange. The direction of the maximum compressional stress that we obtain is N100°~120°E, compatible with that of plate convergence. During the most recent stage of collision, between the Eurasian plate (eastern Central Range of Taiwan) and the Philippine Sea plate (Coastal Range), a major fault zone developed along the innately weak zone of me ´lange, further increasing the shear deformation pattern of the Lichi Me ´lange. This Longitudinal Valley Fault separates the Eurasian plate and the Philippine Sea plate and is one of the most active faults in Taiwan. It can be considered as the present plate boundary in the Taiwan arc-continent collision terrane. According to our reconstruction, this plate boundary of the Longitudinal Valley originated as a submarine arc-prism boundary.

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