Earthquakes happen…

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

On August 12, 2018, an unusually large earthquake (magnitude 6.4) occurred in northern Alaska, in an area that is being considered for oil and gas drilling. See our seismograms below, and this link:

Large Earthquake in the Arctic National Wildlife Refuge Raises Questions About New Oil Drilling Leases (temblor.net)

Why an earthquake this large happened, in this particular location, and at this particular time remains an enigma.

I think the most important take-home message here is not necessarily the specifics of the oil drilling/environmental issues (although that is, of course, important), but rather that:

We know less about how earthquakes work than is generally thought… Sure plate tectonics explains a lot, but the devil is in the details… Why specific large earthquakes occur where they do, and when they are likely to occur, is usually a mystery…

This is the case in many areas of science that affect people, and that is why Weston Observatory is dedicated to our research, monitoring, and education work, exploring the frontiers of earthquake science.

Alaska_081218_6.4&6.0_AKBC

Alaska_081218_TX_DC_MA

 

Magnitude 5.6 Earthquake in Oklahoma on September 3, 2016

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

On September 3, 2016, a magnitude 5.6 earthquake that occurred in Pawnee, Oklahoma, was recorded by Weston Observatory (see seismogram below). This earthquake is tied with another magnitude 5.6 earthquake in Prague, OK (November 6, 2011) as the two largest known earthquakes in Oklahoma.

OK_090316

For more information about the effects of this earthquake, see:

Oklahoma Quake Prompts Shutdown of Gas-Linked Wells (USA Today) 

Check back here for updates on this earthquake.

Additional information about this earthquake can also be found on the U.S. Geological Survey earthquake monitoring web site.

Magnitude 7.0 Earthquake in Japan on April 15, 2016

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

On a April 15, 2016, a magnitude 7.0 earthquake that occurred on the Kyushu Island of Japan, was recorded by Weston Observatory (see seismogram below). The strong signal at the bottom few hours of the seismogram is the Japan quake. The other strong signals are other earthquakes that also occurred on the same day. The signal at the top is a magnitude 6.4 earthquake in Vanuatu, and the smaller signal about an hour before the Japan quake is a magnitude 6.1 earthquake that occurred in Guatemala.

Japan_041516_NESN_WES

Today’s magnitude 7.0 Japan quake occurred very near a magnitude 6.2 quake that occurred two days earlier. There is, of course, the likelihood of strong aftershocks of today’s main shock, but there is no way of knowing whether or not the occurrence of these two events would lead to any more large earthquakes in this area.

A tsunami warning was initially issued for this earthquake, but the warning was later lifted.

Check back here for updates on this earthquake.

Additional information about this earthquake can be found on the U.S. Geological Survey earthquake monitoring web site.

 

Students Use BC Library Seismograph to Monitor Earthquakes and Storms, and Test Prototype of Seismographs in Public Places

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

Weston Observatory and the Boston College Lynch School of Education recently installed a seismograph in the BC O’Neill Library (first floor study area). This seismograph display is a prototype of our new version of seismographs operating in public places.

BC_Library_Blog_Fig1
Figure 1: Seismograph display in the Boston College O’Neill Library.

Our first recorded earthquake at this site occurred beneath the Kamchatka Peninsula of Russia . Because the epicentral area is sparsely populated and the earthquake was 100 miles deep, this earthquake is not likely to have caused serious damage or casualties.

 BC_Library_Blog_Fig2
Figure 2: Earthquake recorded by the BC O’Neill Library seismograph.

On January 23-25, we recorded a snowstorm in the Boston area, as well as a magnitude 7.1 earthquake that occurred in Alaska.

 BC_Library_Blog_Fig3
Figure 3: Snowstorm and Alaska earthquake recorded by the BC O’Neill Library seismograph.

 

Seismic Monitoring of North Korea Nuclear Tests

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

People have been asking why Weston Observatory didn’t record the recent “seismic event” in North Korea.

It was much too small (magnitude 5.1) for us to see it this far away at our New England Seismic Network (or BC-ESP) stations. For us to see a seismic event at that distance, it would probably have to be about a magnitude 6.0 or higher. However, Weston Observatory seismologists also track recordings at seismic stations operated by collaborating observatories that are closer to North Korea.

Here are the seismograms at Weston, MA where it wasn’t recorded and at the IRIS/USGS station at Mudanjiang, China (MDJ) where it was recorded very well. This figure shows the MDJ seismogram and also the “spectrogram” (multi-colored plot, calculated by Dr. Jay Pulli, Visiting Scholar at Weston Observatory).

NKorea_010616_Fig1(Click to enlarge.)
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In this next figure (from IRIS and USGS) you can see the 1/6/2016 event seismogram, superposed on three other seismograms of previous North Korea nuclear tests. The seismograms are so similar that it is hard to distinguish the 2016 event (shown in red). This was one of the first clues that the event was probably a North Korea nuclear test. The biggest difference is just the relative sizes of the nuclear tests.
NKorea_010616_Fig2(Click to enlarge.)
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​Seismologists will be studying these, and other, seismograms of North Korea nuclear tests for forensic analysis of details of the nature of the 1/6/2016 event.

Spectrograms: Visualizing How the Frequency of Seismic Waves Varies With Time

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences, Boston College

These (very cool, and beautiful, I think) graphics are “spectrograms” of some of our recordings of the magnitude 4.7 earthquake that recently occurred in Oklahoma.

The seismograph in Texas is operated by Kristi Rasmusson Fink, and the seismographs in MA are operated by Weston Observatory. The data processing was done by Jay Pulli.

A spectrogram is a particular way of visualizing the vibrations present in a seismogram. It shows how the frequency of the motion varies over time, and how different frequencies of vibration appear at different times in the record. Yellow colors represent stronger signals, and blue colors represent weaker signals.

spectograms

More (Fracking Related?) Oklahoma Quaking…

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences, Boston College

Just this past week alone, there have been 32 earthquakes detected in Oklahoma (magnitude 2.0 to 4.7). Our seismograms and “spectrograms” of today’s magnitude 4.7 quake are shown below.

(The seismograph in Texas is operated by Kristi Fink and the seismographs in MA are operated by Weston Observatory. The data processing was done by Jay Pulli.)

113015_Spectrograms