The deep earthquakes of 1921-1922 in Northern Peru

Emile A. Okal*, Craig R. Bina

*Corresponding author for this work

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

We present a detailed analysis of the 1921 and 1922 deep events in Northern Peru, which we identify as the only reliably located earthquakes in the vicinity of the great 1970 deep Colombian shock. All other reported seismicity in a three-dimensional radius of 550 km centered on the 1970 hypocenter is erroneous, and can be relocated to other seismic provinces. The 1921-1922 earthquakes relocate approximately 230 km to the south of the 1970 event, at depths of 630 km and 660 km, respectively. A combination of centroid moment tensor inversion and forward modeling using ray theory and reflectivity synthetics yields focal mechanisms indicating down-dip compression and seismic moments of 1.2 × 1027 dyn cm and 6 × 1027 dyn cm, respectively. The 1921, 1922 and 1970 events take place on a piece of subducted Farallon plate aged approximately 55 Ma, i.e., anomalously young to support deep seismicity. We suggest that this unusual seismic activity may be due to a local heterogeneity on the slab, whose nature, however, remains unknown.

Original languageEnglish (US)
Pages (from-to)33-54
Number of pages22
JournalPhysics of the Earth and Planetary Interiors
Volume87
Issue number1-2
DOIs
StatePublished - Jan 1 1994

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

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