(8:30:20 PM (October 31) Pacific Daylight Time)
Epicenter: Latitude 8.854°N, 145.315°E (indicated by arrow on map below).
Depth: 248 kilometers.
Robert Butler and John Lahr
A large earthquake occurred last evening Portland time on the subduction zone at the Mariana Trench about 40 km (25 miles) west-northwest of Agrihan and 405 km (250 miles) N of Saipan. Because this earthquake occurred deep below the surface of the Earth, no tsunami was produced. This earthquake occurred within the Pacific Plate that is subducting into the deeper mantle at the Mariana Trench where the Pacific and Philippine plates converge. The Pacific Plate is over 150 million years old at the Marianas Trench. This means it is old, cold, and dense with the result that it subducts at a steep angle as it dives beneath the Philippine Plate at the Marianas Trench.
Corvallis AS-1 Record with 8 s to 25 s band-pass filter applied.
Robert Butler's Portland AS-1 Record