HR: 08:00h
AN: S41A-01    [PDF]
TI: Measuring Active Faulting in Bolivia: the 1998 Aiquile Earthquake
AU: * Funning, G J
EM: garethf@earth.ox.ac.uk
AF: COMET, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AU: Barke, R
EM: richba@earth.ox.ac.uk
AF: COMET, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AU: Lamb, S H
EM: simon.lamb@earth.ox.ac.uk
AF: COMET, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AU: Minaya, E
EM: estelam@earth.ox.ac.uk
AF: Observatorio San Calixto, Calle Indaburu 944, La Paz, 12656 Bolivia
AU: Parsons, B E
EM: barry.parsons@earth.ox.ac.uk
AF: COMET, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AU: Woodhouse, J H
EM: john.woodhouse@earth.ox.ac.uk
AF: COMET, Department of Earth Sciences Parks Road, Oxford, OX1 3PR United Kingdom
AB: The Aiquile region of central Bolivia is situated in the core of the actively deforming Bolivian Orocline. Palaeomagnetic data show that differential rotations consistent with oblique convergence have continued over the past 10 Myr. Structural mapping of the sub-Andean fold-and-thrust belt to the east shows that the majority of this convergence has occurred there as shortening; however there exists a significant transverse component of motion which must be accommodated as strike-slip faulting elsewhere. Many topographic lineations assumed to be related to strike-slip faulting have been identified in the area around Aiquile, however none has been associated with large earthquakes or demonstrated to be active over the past million years. On 22nd May 1998, a $M_w = 6.5$ earthquake struck the region, the largest shallow earthquake to occur in Bolivia for 50 years, resulting in over 105 fatalities and rendering thousands homeless in the towns of Aiquile and Totora and their surrounding villages. Seismic observations of the event are inconclusive; the correct orientation and style of the faulting -- either right-lateral strike-slip on a N--S fault, or left-lateral on an E--W fault -- cannot be determined as large uncertainties in earthquake location mean we do not know \emph{a priori} which of the two nodal planes in the focal mechanism is the fault plane, or upon which structure the earthquake occurred. We present here the first study of a Bolivian earthquake using InSAR. Despite the rugged nature of the terrain in the Aiquile region, with its sharp changes of relief ($\sim$ 3000 m over 20 km) -- a consequence of its location between the high Altiplano to the west and the foreland basin to the east -- we demonstrate that by using freely-available SRTM digital elevation data we can correct for topographic artifacts and generate a clear deformation signal. Our preferred model is for slip on a N--S-striking fault, with a location which validates Modified Mercalli Intensity maps constructed from field observations and local damage reports.
DE: 1208 Crustal movements--intraplate (8110)
DE: 1243 Space geodetic surveys
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 7215 Earthquake parameters
DE: 8005 Folds and folding
SC: Seismology [S]
MN: 2003 Fall Meeting