Colluvial wedges associated with pre-historical reverse faulting paleoearthquakes
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Colluvial wedges collapsed from fault scarp can also be used to study reverse faulting paleoearthquakes. Generating processes of reverse faulting colluvial wedges are much more complex than those associated with normal faulting earthquakes. Reverse faulting colluvial wedge is also in triangle shape, and dies away from the fault. Contact between the fault and the colluvial wedge may be a simple straight reverse fault or a combination of an erosive surface in the upper part and a reverse fault in the lower part. Contents and grain sizes increase near the fault and along the base of a colluvial wedge. Based on examples from the piedmont reverse fault and fold along the northern Tainshan, we studied characteristics of reverse faulting colluvial wedges, and discussed the generating processes of reverse faulting colluvial wedges. Reverse faulting generates an unstable scarp hanging in the air immediately after an earthquake. Fallen material deposits along the base of newly formed fault scarp. Erosive surface and surface of colluvial wedge form an antithetic scarp with an opposite direction to underlain reverse fault. If the later stage colluvium covers both the early stage colluvium and the erosive surface, the colluvial wedge will have a curved vertical edge with reverse fault in the lower part and erosive surface in the upper part. If the erosive surface is not covered by later stage colluvium, the colluvial wedge will only have a simple straight vertical edge, which is the reverse fault. A colluvial wedge represents a paleoearthquake event, but the height of the wedge is not equal to vertical offset of the paleoearthquake.
Keywordscolluvial wedge paleoearthquake fault rupture active reverse fault
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