Another Earthbound Shake Up

9 Feb

On Tuesday, January 23rd the Pacific tectonic plate slid a tiny amount under the North American tectonic plate causing a magnitude 7.9 earthquake southeast of Kodiak Island in the Gulf of Alaska. The epicenter of the earthquake is depicted on the map below from the United States Geologic Survey (USGS). The red line on the map depicts where the two tectonic plates meet, forming the fault line. As the Pacific and North American tectonic plates meet each other they are moving about 59 mm each year. This is why earthquakes are common in the Pacific-North America plate boundary region south of Alaska. Over the last 100 years, 11 other magnitude 7+ earthquakes have occurred within 600 km of the January 23rd, 2018 earthquake. This earthquake is shown as an oval on the map, not a single point. That is because this earthquake was generated when an area of the plates 230 km long and 30 km wide strike and slip over each other.

So why do we care about an earthquake that occurred over 3,600 miles away? Did you feel it? You may not have felt it, but the seismograph at our Ada & Archibald MacLeish Field Station located about 10 miles from Smith College campus felt the shock waves (see below). The seismograph at MacLeish is part of a vast network of stations across the entire country recording earth movements. We may think of the ground as terra firma, but when two tectonic plates rub against each other the ground wiggles like brown pudding.

To get a sense of the ripple effect of the earth from the earthquake, click on the map below to watch the vertical motion video map of the Alaskan earthquake. In this video, red dots represent vertical motion up and blue dots represent down vertical motion of the ground.  It is clear that the clash of the plates sent shock waves across North America and beyond. There was our beloved terra firma rippling like water.

Submitted by Paul Wetzel, Environmental Research Coordinator, CEEDS

With information from the USGS and IRIS DMC (2010), Data Services Products: GMV The Ground Motion Visualization, doi:10.17611/DP/16325361.

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