Reconstructing Earthquake-Driven Erosion in the Southern Alps, New Zealand using the Sedimentary Record
Abstract
Studies of active mountain belts have concluded that large earthquakes are significant drivers of erosion. However, relatively few studies have directly quantified the volume of earthquake-driven erosion because these events occur infrequently and are rarely recorded using instrumental measures of erosion such as suspended sediment yield from rivers. Deposits in sedimentary basins adjacent to mountain belts afford the possibility of developing records of mountain building processes that capture the impact of large earthquakes. This paper reports a study of erosion and depositional processes over multiple seismic cycles that are preserved in a small lake in South Westland, New Zealand. The sedimentology of three 6m cores was investigated using high resolution grain-size, TOC and C:N ratios to identify the sedimentary record of co-seismic mass wasting in Lake Paringa. The co-seismic sedimentary signature consists of megaturbidites that exhibit complexly graded fine sandy bases, overlain by normally graded silts and a clayey silt cap. High resolution radiocarbon dating shows that the megaturbidites record the 1717 AD (Mw > 7.9), 1620 AD (Mw > 7.6) and 1430 AD (Mw >7.9) Alpine Fault earthquakes; and two additional Alpine Fault earthquakes between 1166-1061 AD and 868-449 AD. The co-seismic sedimentation is followed by a sequence of normally graded turbidites that are interpreted as the sedimentary product of increased post-seismic erosion. The post-seismic turbidite sequences are overlain by sediments deposited in quiescent depositional conditions. Together these two phases of deposition represent sedimentation over a complete seismic cycle and provide the basis for reconstructing erosion driven by Alpine Fault earthquakes. Over the last ca. 1200 years five ruptures of the Alpine Fault have contributed nearly half of the total erosion in the catchments that drain into Lake Paringa. These new insights into sedimentary responses to co- and post- seismic disturbance open the possibility of deriving catchment denudation rates and quantifying the role of large earthquakes in the mass flux from range-front catchments.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP41D0639H
- Keywords:
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- 8175 TECTONOPHYSICS / Tectonics and landscape evolution;
- 4313 NATURAL HAZARDS / Extreme events