1938 Earthquake

1938 Earthquake. . , Side A , Since 1872 only one earthquake centered in Minnehaha county has been recorded. A mild quake with an intensity of IV on the Mercalli scale and a magnitude of 4.1 on the Richter scale affected 5000 square miles in this region and 3:37 a.m. on October 11, 1938. Mercalli's scale relates to damage resulting from earthquakes while their size is measure by Richter's scale. , Alarmed residents made more than 50 calls to Sioux Falls police to report houses jarred, dishes and windows rattled, and loose objects swayed by , Side B , the relatively weak tremor. No injuries or deaths resulted. , This earthquake was caused by isostatic rebound. During the Ice Age, glaciers weighing millions of tons compressed the earth's crust; as they retreated, the crest slowly began to rebound. In October 1938 an adjustment in the crust suddenly released energy, the ground trembled, and vibrations radiated out from the focus. , This site is near the epicenter, the point on the surface of the earth above the focus, which is the point within the earth where energy was abruptly released. ,