Massive Mexican Earthquake Captured on DTM Seismometer
On 8 September 2017 at 04:49:21 UTC, a powerful M8.1 earthquake, 87 km southwest of Pijijiapan, Mexico, occurred at a shallow depth of 69.7 km. The epicenter of the quake was 102 miles west of Tapachula in southern Chiapas state.
According to staff scientists Diana Roman and Lara Wagner, DTM owns a cache of broadband seismometers that are normally deployed in field experiments worldwide. However, as we are currently in between field experiments, and as there is a large-scale construction project going on next door to our campus, we have been running two of these seismometers in labs on campus to monitor construction-related vibrations that may affect some of the sensitive geochemical instrumentation housed at BBR. Both on-campus seismometers clearly recorded waves from last week's M8.1 earthquake in Chiapas, approximately 3000 km (2000 miles) away from Broad Branch Road. Although the vibrations were far too small to be felt by people on the BBR campus, our instruments are sensitive enough to record them clearly.
This is not unusual – seismometers commonly detect waves from large earthquakes anywhere on Earth. These recordings can then be used to study both the earthquake and the structures between the earthquake and the station.
Raw (uncalibrated) data from a DTM seismometer (courtesy Field Seismologist Steven Golden/DTM).
The screenshot shown was taken during the very first look at the data. The three seismograms in the graph show three components (vertical, North-South, and East-West) of ground velocity (uncalibrated), all measured simultaneously by the same instrument.
The shown subset of the seismograms covers about one hour of data, starting around 4:50 UTC (12:50 AM local). According to the USGS, the magnitude 8.1 earthquake started at 04:49:21 UTC, with its epicenter located about 87 km (54 miles) Southwest of the Pacific coastline of Chiapas, Mexico. According to the graph above, it took around 7 to 8 minutes for the first seismic waves to reach Washington DC. Body waves, that took the shortcut through the body of the Earth, arrive first, followed by the much larger but slower surface waves. The latter show an effect called 'dispersion', where longer period waves arrive a bit earlier than shorter period waves due to differing velocities.
Image source: USGS
More information on this Earthquake and its geological setting can be found on the USGS Web site: https://earthquake.usgs.gov/earthquakes/eventpage/us2000ahv0#executive
Written by: Stephen Golden, Diana Roman, Lara Wagner