Wednesday, November 4, 2015

1936 earthquake rocks Milton-Freewater area

On July 15, 1936, at 11:08 p.m., an earthquake registering between 5 and 5.5 on the Richter scale shook residents of the Milton-Freewater area out of their beds. The strongest shock hit the Stateline area, cracking the pavement there, in places up to two meters wide, and at one point the ground dropped by 2.4 meters (7.9 feet). The shaking started slowly and lasted for 15 seconds; more than 54 aftershocks were reported by George Harshman of Freewater following the initial shock, and they continued intermittently until November 17.

The East Oregonian reported the earthquake was felt as far west as Arlington and as far north as Spokane, and severely damaged buildings in Walla Walla, Milton-Freewater and Athena. Residents of Pilot Rock, Pendleton and even Heppner fled their homes and businesses during the quake.

Among the reported damage: Homes in the area were uninhabitable due to large cracks in the walls, and chimneys and flues were shaken loose from roofs; a meat market and bank in Athena, joined together before the quake, were separate buildings the following morning; two freight cars were shaken off the tracks at Blue Mountain Station, and large rocks the size of cars bounced into the intersection of Souther Creek Road and Walla Walla River Highway; the Rev. J.M. Marlatt’s concrete home fell to the ground; and the quake shook loose artesian wells in the area — one on the A.M. Fix ranch that had dried up three weeks earlier, and another new artesian well from a previously shared well on the farm of Walter Maxson.

In some of the places where ground cracks appeared, water also was present in the cracks, signaling liquefaction of the soil. Liquefaction (when the soil temporarily loses strength and acts like a liquid) can cause extensive damage, bringing underground infrastructure like water and sewer lines to the surface and even swallowing people, buildings and cars whole in seconds during larger quakes, especially if the ground is already saturated with water.

The epicenter of the 1936 earthquake was fixed at 10 kilometers (6.38 miles) northwest of Milton-Freewater. It occurred along the Wallula fault system, which runs from near Milton-Freewater to Kennewick, Wash., along the Horse Heaven Hills, and is part of the larger Olympic-Wallowa Lineament that reaches from the Wallowa Mountains to the Olympic Peninsula.

Our corner of Northeast Oregon is still seismically active, though the magnitude of earthquakes is generally below 4 on the Richter scale. The Milton-Freewater area has recorded 66 earthquakes since 1931, the largest in recent history a 4.3 quake in November 1991. The most recent earthquake was Jan. 23, 2015, centered 4.7 miles southwest of Athena; it registered 3.7.

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