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On trapdoor faulting at Sierra Negra volcano, Galapagos Sigurjon Jonssona,*, Howard Zebkerb

Summary: On trapdoor faulting at Sierra Negra volcano, Gala´pagos
Sigurjo´n Jo´nssona,*, Howard Zebkerb
, Falk Amelungc
Institute of Geophysics, ETH Ho¨nggerberg, CH-8093 Zu¨rich, Switzerland
Geophysics Department, Stanford University, Stanford, CA 94305, USA
Division of Marine Geology and Geophysics - RSMAS, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA
Accepted 16 November 2004
Rapid uplift observed during 1992­1997 at Sierra Negra volcano, western Gala´pagos, was followed by deformation that we
have previously interpreted as trapdoor faulting on an intra-caldera fracture system. At that time, no direct evidence for the
trapdoor faulting was available to support this interpretation. Here we report field evidence of recent faulting at Sierra Negra and
provide direct measurements of the faulting using pixel offsets between satellite radar amplitude (backscatter) images. Our field
observations, carried out in 2001, indicate that recent faulting occurred along the southern part of the intra-caldera fault system
with maximum offset of at least 0.5­1 m. Differences between two satellite radar amplitude images show 1.4F0.2 m range
change across this fault system. This suggests that 1.5F0.2 m of faulting occurred, assuming vertical ground displacements,
consistent with our previous modeling results. Results of numerical modeling indicate that growing sills can cause faulting of
the intrusion roof on outward-dipping or nearly vertical faults. This occurs at high excess magma pressure when the lateral


Source: Amelung, Falk - Rosenstiel School of Marine and Atmospheric Sciences, University of Miami


Collections: Geosciences