GRMI, GRCC’s seismometer, housed in the geology lab in Calkins Science Center, has been busy in the past month.
GRMI recorded the July 29th magnitude 8.2 earthquake outside of Perryville, Alaska. The primary waves (body waves that travel through the Earth) arrived at our station 10 minutes after the quake. The L-waves (wave that travel across the surface of the Earth) arrived at GRMI 27 minutes later! The earthquake took place where the Pacific Plate is being shoved (subducted) under the North American Plate. These types of quakes can generate tsunami. A tsunami warning was issued but later cancelled. Click here to learn more about this earthquake.
On August 14th, GRMI recorded the magnitude 7.2 earthquake in Haiti. The earthquake was located 78 miles (125 km) west of the capital city of Port-au-Prince at a depth of 6.2 miles (10 kilometers). The primary waves arrived in Grand Rapids within 5 minutes! The L-waves arrived at our station less than 15 minutes later. The earthquake took place along the Enriquillo-Plantain Garden fault zone. This fault zone is the result of the sliding and converging of the Caribbean and North America tectonic plates. The earthquake was similar in magnitude to the devastating 2010 earthquake which is ranked as one of the deadliest earthquakes in history. Click here and here to learn more about this most recent earthquake in Haiti.
Visible in the image of the Haiti seismogram, is the trace of a magnitude 6.9 aftershock from the July 29th Alaska earthquake, 3 weeks after the main shock! It is important to note that earthquakes commonly occur in swarms. The largest earthquake in a swarm is the main earthquake and those that occur before and after are called the foreshocks and aftershocks, respectively. A magnitude 6.9 earthquake is still a very large earthquake and can cause significant damage in inhabited areas; however, the main shock was a magnitude 8.2 earthquake, which means it released well over 30 times the energy of the 6.9 aftershock!