HR: 0800h
AN: T51D-0759    [Abstracts]
TI: Coastal land loss and gain as potential earthquake trigger mechanism in SCRs
AU: * Klose, C D
EM: christian@cdklose.com
AF: Columbia University, School of Engineering and Applied Science, 351 Mudd Bldg., New York, NY 10027, United States
AB: In stable continental regions (SCRs), historic data show earthquakes can be triggered by natural tectonic sources in the interior of the crust and also by sources stemming from the Earth's sub/surface. Building off of this framework, the following abstract will discuss both as potential sources that might have triggered the 2007 M_L4.2 Folkestone earthquake in Kent, England. Folkestone, located along the Southeast coast of Kent in England, is a mature aseismic region. However, a shallow earthquake with a local magnitude of M_L = 4.2 occurred on April 28 2007 at 07:18 UTC about 1 km East of Folkestone (51.008° N, 1.206° E) between Dover and New Romney. The epicentral error is about ±5 km. While coastal land loss has major effects towards the Southwest and the Northeast of Folkestone, research observations suggest that erosion and landsliding do not exist in the immediate Folkestone city area (<1km). Furthermore, erosion removes rock material from the surface. This mass reduction decreases the gravitational stress component and would bring a fault away from failure, given a tectonic normal and strike-slip fault regime. In contrast, land gain by geoengineering (e.g., shingle accumulation) in the harbor of Folkestone dates back to 1806. The accumulated mass of sand and gravel accounted for a 2.8·10⁹ kg (2.8 Mt) in 2007. This concentrated mass change less than 1 km away from the epicenter of the mainshock was able to change the tectonic stress in the strike-slip/normal stress regime. Since 1806, shear and normal stresses increased at most on oblique faults dipping 60±10°. The stresses reached values ranging between 1.0 KPa and 30.0 KPa in up to 2 km depth, which are critical for triggering earthquakes. Furthermore, the ratio between holding and driving forces continuously decreased for 200 years. In conclusion, coastal engineering at the surface most likely dominates as potential trigger mechanism for the 2007 M_L4.2 Folkestone earthquake. It can be anticipated that the mainshock nucleated at shallower depth (<500 m) near the Paleozoic surface a) where differential stresses are generally maximum and b) because earthquakes in aseismic regions are generally overestimated by 88% due to sparse instrumental coverage. The latter was suggested by recent research on shallow seismicitiy (<10 km) in SCRs in northeastern USA and eastern Canada. Data of the focal mechanism provided by the British Geological Survey (BGS) confirm fault zone orientations of 326°/74° (strike-slip fault component) and 71°/48° (normal fault component).
UR: http://www.earthquakes.bgs.ac.uk/earthquakes/reports/folkestone/folkestone_28_april_2007.htm DE: 1630 Impacts of global change (1225)
DE: 3238 Prediction (3245, 4263)
DE: 7205 Continental crust (1219)
DE: 8168 Stresses: general
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: 2007 Fall Meeting