Scientists at the South Carolina Earthquake Education and Preparedness program in the College of Charleston’s Department of Geology and Environmental Geosciences have begun analyzing the seismograms from magnitude 4.1 earthquake near Edgefield, South Carolina. 

Figure 1:  Three component seismograms from the Feb. 14, 2014 earthquake near Edgefield, South Carolina.  Location of seismometers and the earthquake shown on Figure 2 (below).

Figure 1: Three component seismograms from the Feb. 14, 2014 earthquake near Edgefield, South Carolina. Location of seismometers and the earthquake shown on Figure 2 (below).

[Related: Why scientists say we sit on a bowl of Jello.]

The seismograms from this earthquake (Figure 1) clearly show the effect of the sediments of South Carolina’s coastal plain on the strength of ground motion.  Seismometer 158A in Hollywood, South Carolina (west of Charleston) clearly shows stronger motion in the horizontal directions (North-South and East-West) than W54A in Campobello, South Carolina (in the upstate).  This occurs even though W54A is closer to the earthquake than 158A (Figure 2).  This shows that the same magnitude earthquake in the Low Country of South Carolina would be expected to cause greater damage than a similar size earthquake in the hard rock of the upstate.

The data being analyzed come from the seismometers of the EarthScope program’s USArray, a National Science Foundation supported program that maintains a pool of 400 seismometers that have been moving across the USA, starting in California in 2003.  The USArray seismometers arrived in South Carolina in early 2013.  Some will stay permanently in South Carolina and others will be moved to Alaska starting in late 2014.

Figure 2:  Location of M=4.1 earthquake (red symbol) together with location of seismometers (green symbols) shown in Figure 1, superimposed on a map of South Carolina with state and county borders.

Figure 2: Location of M=4.1 earthquake (red symbol) together with location of seismometers (green symbols) shown in Figure 1, superimposed on a map of South Carolina with state and county borders.

[Related: College of Charleston students helped install the USArray seismometers.]

On February 16, 2014, an aftershock of the Valentine’s day earthquake shook Edgefield, South Carolina at 3:23 p.m. It was a magnitude 3.2 earthquake that was not felt in more distant locations, consistent with it being a substantially smaller earthquake.  Friday’s magnitude 4.1 earthquake released nearly 30 times more energy than today’s aftershock.  Based on this, little if any damage is expected from today’s event.  Aftershocks are normal and to be expected from earthquakes the size of the Valentine’s Day earthquake, however, most will be so small that they will not be felt by residents and the size will decrease over time.

For more information, contact Steve Jaume at jaumes@cofc.edu or 843.953.1802.