Magnitude 5.8 – 11km SSE of Lincoln, Montana -AND- Magnitude 6.5 – 3km NNE of Masarayao, Philippines – July 6, 2017

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The distance from Montana to Massachusetts is much closer than the distance from the Philippines to Massachusetts, hence the much larger amplitude seismic waves on our BC-ESP seismographs!!

USGS Event Page for Montana
Magnitude 5.8 – 11km SSE of Lincoln, Montana
2017-07-06 06:30:17 UTC
46.871°N   -112.603°W
13.6 km depth
USGS Tectonic Summary for Montana earthquake:
“The July 6, 2017 M 5.8 earthquake southeast of Lincoln in western Montana occurred as the result of shallow strike slip faulting. The location and focal mechanism solution of this earthquake are consistent with right-lateral faulting in association with faults of the Lewis and Clark line, a prominent zone of strike-slip, dip slip and oblique slip faulting trending east-southeast from northern Idaho to east of Helena, Montana, southeast of this earthquake. In the region of the July 6th earthquake, prominent faults include the St Mary’s-Helena Valley fault, and the Bald Butte fault, both right-lateral structures. More detailed field studies will be required to identify the causative fault responsible for this earthquake.”

USGS Event Page for Philippines
Magnitude 6.5 – 3km NNE of Masarayao, Philippines
2017-07-06 08:03:57 UTC
11.114°N   124.633°E
6.5 km depth
USGS Tectonic Summary for Philippines earthquake:
“The Philippine Sea plate is bordered by the larger Pacific and Eurasia plates and the smaller Sunda plate. The Philippine Sea plate is unusual in that its borders are nearly all zones of plate convergence. The Pacific plate is subducted into the mantle, south of Japan, beneath the Izu-Bonin and Mariana island arcs, which extend more than 3,000 km along the eastern margin of the Philippine Sea plate. This subduction zone is characterized by rapid plate convergence and high-level seismicity extending to depths of over 600 km. In spite of this extensive zone of plate convergence, the plate interface has been associated with few great (M>8.0) ‘megathrust’ earthquakes. This low seismic energy release is thought to result from weak coupling along the plate interface (Scholz and Campos, 1995).

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