1965 Puget Sound earthquake
 Olympia
Seattle
 |
|
| Date | April 29, 1965 |
|---|---|
| Magnitude | 6.7 Mw |
| Depth | 59 km |
| Epicenter | 47°24′N 122°18′W / 47.4°N 122.3°WCoordinates: 47°24′N 122°18′W / 47.4°N 122.3°W |
| Areas affected | (Washington) United States |
| Total damage | $12.5 million |
| Max. intensity | VIII (Severe) |
| Peak acceleration | .204g at Olympia |
| Aftershocks | None |
| Casualties | 7 dead |
The 1965 Puget Sound earthquake occurred at 08:29 PDT (15:29 UTC) on April 29 within the Puget Sound region of Washington State. It had a magnitude of 6.7 on the moment magnitude scale and a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale. It caused the deaths of seven people and about $12.5 million in damage. There were no recorded aftershocks.
The western part of Washington State lies above the Cascadia subduction zone, where the Juan de Fuca Plate is being subducted beneath the North American Plate. The seismicity of this region consists of rare great megathrust earthquakes, like the 1700 Cascadia earthquake and more common earthquakes originating from within the subducting slab. These events relate to normal faulting, associated with the bending of the slab, possibly related to a phase change below about 40 km from basalt/gabbro to eclogite.
The earthquake had an estimated magnitude of 6.6 Ms, 6.5 Mb and 6.7 Mw. At 10–20 seconds the duration of strong ground motion was relatively short.
The earthquake's focal mechanism indicates that it resulted from normal faulting within the Juan de Fuca slab. There were no recorded aftershocks, similar to observations from the 1949 Olympia and 2001 Nisqually earthquakes and a characteristic of such intraslab events.
...
Wikipedia