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

Clear and Simple Illustration of Mechanism to Explain Earthquakes in the Central and Eastern United States

This is a clear and simple illustration (adapted from the South Carolina Earthquake Education and Preparedness Program) of the commonly accepted “ancient zones of weakness” model for the cause of earthquakes in the Central and Eastern United States (and other “intraplate” regions far from plate boundaries). According to this model, preexisting faults and/or other geological features formed during ancient geological episodes persist in the intraplate crust, and, by way of analogy with plate boundary seismicity, earthquakes occur when the present-day stress is released along these zones of weakness.

IP_Quakes_Logs_AdaptedAlso see:

Why Does the Earth Quake in New England? and South Carolina Earthquake Education and Preparedness Program

Please Donate to Support Our Work

If you benefit from these blog posts and feel inspired to contribute to our work, please visit this page and make a donation.

At Weston Observatory, we’ve been busy this year envisioning and building an earthquake observatory for the 21st century, and we are now embarking on a fundraising effort to support our vision.

This year’s fundraising theme is education and public outreach. Funds contributed this year will primarily go towards bringing earthquake and related science into schools and public libraries, supporting our monthly public colloquium for adult learners, and of course towards maintaining this blog.

If you feel inspired to make a contribution, please click here to go to our donations page.

Thank you for any amount, small or large.

WO_Graphic_AK_G_F

Broken Garage Door Springs, Earthquake Prediction, and Earthquake Triggering

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

(Originally Posted: April 27, 2012)

A few days ago, one of the huge springs on our garage door opener broke, with quite a big KABOOM!

It seems to me that this is a perfect example of the problem of earthquake prediction. Here’s what I see as the connection:

In the morning, the garage door repair guy (who happened to be there fixing something else) looked up at the spring and said, “That deformed spot in the spring is ‘metal fatigue’ – it might break in 5 minutes, or it might break in 10 or 20 years.” Then, two hours later, it broke! (Perhaps he disturbed the internal stress field while he was fixing something else?)

This seems to be a perfect analog of the Elastic Rebound Theory of earthquakes, and the phenomenon of Earthquake Triggering!

It also explains why we knew that an earthquake was lurking in Haiti, but we couldn’t tell when it would occur: The tectonic stresses were ready to be released in an earthquake, but nobody could tell if the earthquake would occur in minutes, in years, in decades, or in centuries…

New Updated Seismicity Maps for Northeast U.S.

Click on the maps below to see the Weston Observatory seismicity maps of the Northeast United States, updated as of early February 2014.

The first map shows historical seismicity (from June 1638 to December 1974), and the second map shows network seismicity (from January 1975 to early February 2014).

NEUS_Historical_Seis_Sm

NEUS_Network_Seis_Sm

The Detective Work of Seismologists: Earthquake or Blast?

Justin Starr
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

Residents of the city of New Bedford, MA and the surrounding area felt something very strange at 10:52 am on January 9th, 2014. They heard a loud blast and felt a distinct rumble.

A seismic event had occurred.

Weston Observatory scientists quickly determined that the magnitude of this seismic disturbance was 1.9 and that it was located very close to New Bedford. Not very big, but shallow enough to be heard by many people in the area.

While speaking to the Massachusetts Emergency Management Agency (MEMA), Weston Observatory scientists were informed that there may have been blasting in the New Bedford harbor around the same time as the earthquake and very close to the possible epicenter. So was this a real earthquake? It was up to the scientists to find out.

Several phone calls went out and eventually, Weston Observatory scientists reached the New Bedford harbormaster who put them in touch with the Captain of… the Kraken! The Kraken is a drilling and blasting barge located in New Bedford and is tasked with widening the shipping lanes. As it turns out, the Kraken did not blast until 12:09 pm, over an hour after the earthquake occurred. In fact, the Captain received many phone calls asking if it was they who blasted and caused the shaking… but it was the earthquake!

New_Bedford_010914_Fig1

The two seismograms shown below are from a USArray seismic station in Tiverton, RI. On those seismograms, you can see the Kraken Blast and the earthquake. Notice the big difference in magnitude (the earthquake is an order of magnitude larger).

New_Bedford_010914_Fig2

And notice (below) the well-defined, high amplitude wave labelled “Rg” on the seismogram of the blast. The presence of these “Rg” waves on a seismogram are one of the ways that seismic “detectives” use to identify blasts, and distinguish them from earthquakes.

New_Bedford_010914_Fig3

These “Rg” waves have been studied by seismologists, and are one of the ways that seismologists can distinguish between earthquakes and explosions. See, for example:

Kafka (1990): Rg as a Depth Discriminant for Earthquakes and Explosions