TY - JOUR
T1 - The deep earthquakes of 1921-1922 in Northern Peru
AU - Okal, Emile A.
AU - Bina, Craig R.
N1 - Funding Information:
It is a pleasure to thank Ota Kulhanek for access to the superb archives at Uppsala. We are grateful to our collaborators on the historical CMT project, Wei-Chuang Huang, Göran Ek-strom and Misha Salganik, for unraveling the moment tensors of the 1911 and 1922 events, and to Tim Clarke for allowing us to use his reflectiv- ity code. We thank Elizabeth Campbell for help in the relocations, and Steve Kirby for many discussions on the seismicity of Benioff zones. Heidi Houston and an anonymous reviewer provided useful comments on the early draft of the manuscript. One of us (E.A.O.) thanks Fr. Bernard Lahn for providing quarters at Kayser Cob-lege, Nauru, in October 1993, where superb isolation turned out to be most conducive to scientific writing. This research was supported by the National Science Foundation under Grants EAR-91-58594 (C.R.B.) and EAR-93-16396 (E.A.O.).
PY - 1994/12
Y1 - 1994/12
N2 - 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.
AB - 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.
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U2 - 10.1016/0031-9201(94)90020-5
DO - 10.1016/0031-9201(94)90020-5
M3 - Article
AN - SCOPUS:0028563957
SN - 0031-9201
VL - 87
SP - 33
EP - 54
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
IS - 1-2
ER -