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A reassessment of the rupture characteristics of oceanic transform earthquakes

Summary: A reassessment of the rupture characteristics of oceanic transform
Rachel E. Abercrombie1
and Go¨ran Ekstro¨m
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Received 27 July 2001; revised 21 November 2002; accepted 23 January 2003; published 1 May 2003.
[1] We investigate the long-period source spectra of oceanic transform earthquakes and
find that previously proposed slow rupture components can be explained as artifacts
generated by the modeling procedure. We use low-frequency ( 20 mHz) Rayleigh and
Love waves to calculate the amplitude spectra of five earthquakes on the Romanche and
Chain transform faults in the equatorial mid-Atlantic Ocean. We find that errors and
approximations in the centroid depth, focal mechanism, and earth structure at the source
have significant effects on the shape of the source spectra. If global catalog values and
an average crustal model are assumed, the spectra exhibit apparent anomalous energy at
long periods which has previously been interpreted as a result of slow rupture. We
recalculate the source spectra using precise, independently determined depths and moment
tensors and a more realistic oceanic crustal structure in the source region. The resulting
source spectra are flat at long periods with no indication of anomalous long-period energy.
Our results imply that oceanic transform earthquakes do not commonly have detectable
slow rupture components. INDEX TERMS: 7209 Seismology: Earthquake dynamics and mechanics;


Source: Abercrombie, Rachel E. - Department of Earth Sciences, Boston University


Collections: Geosciences