1947 Satipo earthquake
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  | |
| UTC time | 1947-11-01 14:58:57 |
|---|---|
| ISC event | 898103 |
| USGS-ANSS | ComCat |
| Local date | November 1, 1947 |
| Local time | 09:58:57 |
| Magnitude | 7.6–7.7 Mw |
| Depth | 22 km (14 mi) |
| Epicenter | 10°58′23″S 74°43′30″W / 10.973°S 74.725°W |
| Areas affected | Peru |
| Max. intensity | MMI IX (Violent) |
| Landslides | Yes |
| Casualties | 233–2,233 dead |
The 1947 Satipo earthquake was the largest earthquake in the sub-Andean region of Peru. It occurred on November 1 at 09:58:57 local time with an epicenter in the Department of Junín. The earthquake had an estimated moment magnitude (Mw ) of 7.6–7.7 and focal depth of 22 km (14 mi). It was caused by dip-slip movement on a shallow-angle fault. The earthquake caused severe damage in the towns of Satipo and La Merced, and was felt several hundred kilometers away in Iquitos and Lima. It also triggered widespread landsliding in the region. Landslides along the Satipo River caused it to flood, leaving thousands homeless and possibly causing drowning people. The total death toll from the earthquake was between 233 and 2,233.
Earthquakes in Peru are mainly concentrated at the subduction zone where the Nazca Plate subducts beneath the South American Plate at the Peru–Chile Trench off its west coast. Another zone of seismicity is recorded within the South American Plate in the Andes region. In the high Andes, shallow earthquakes are the result of normal-faulting such as the 1946 Ancash earthquake which ruptured a shallow-dipping fault oriented parallel to the range. The western margin of the Cordillera Blanca in central Peru exhibits normal-faulting and coincides with extensional tectonics acting perpendicular to the range.[1]
While normal-faulting is the dominant mechanism, parts of the western sub-Andes experience thrust tectonics. This zone is located between the high Andes and Amazonian craton and is characterised by active fold and thrusting since the Pliocene. The occurrence of northwest-trending, west-dipping thrust faults in the belt suggest the Amazonian craton is being thrusted beneath the Cordillera Oriental. A possible cause of these earthquakes is intraplate deformation in response to subduction of the Nazca Plate. Most thrust earthquakes in the region occur on steep-angled fault planes ranging from 30 to 60° at depths of 10 to 38 km (6.2 to 23.6 mi), corresponding to the lower crust and upper mantle. [2]
Earthquake
The mainshock occurred on 1 November at 14:58:57 UTC (09:58:57 local time) with an epicenter about 136 km (85 mi) south–southwest of Huancayo, in Junín province.[3] It was a shallow intraplate earthquake that occurred within the South American Plate, having a focal depth of 22 km (14 mi), and was the largest of its kind ever recorded in the sub-Andean region.[1] The United States Geological Survey measured the earthquake at 7.5 on the surface-wave magnitude scale and 7.6–7.7 by the International Seismological Centre on the moment magnitude scale.[1][4][5]
The aftershocks that followed had epicenters distributed east of the mainshock. An analysis of data from seismic stations in Weston, Pasadena and Saint-Maur indicated that the mainshock was caused by vertical movement on a north-oriented fault plane that dipped 30°. The inferred dip angle was shallower than that of faults surveyed in the region. Within the epicenter region, two other earthquakes larger than magnitude 6.0 were recorded. In 1976, a Ms 6.6 strike-slip earthquake occurred south of the 1947 earthquake epicenter at 5 km (3.1 mi) depth, and a Mw 6.5–6.8 shock in 1982 occurred north of the 1947 earthquake with a left-lateral–reverse mechanism.[1]