From temblor: “Earthquake in Greenland triggers fatal landslide-induced tsunami”

1

temblor

June 19, 2017
David Jacobson

1
This picture shows the settlement of Nuugaatsiaq, which was hit by a tsunami over the weekend. The tsunami was triggered by a landslide following a M=4.1 earthquake. (Photo from: knr.gl)

Over the weekend, a M=4.1 earthquake on Greenland’s western coast caused a massive landslide, triggering a tsunami that inundated small settlements on the coast. At this stage, four people are feared to have died, nine others were injured, and 11 buildings were destroyed. In the hardest hit village, Nuugaatsiag, which is home to around 100 people, 40 people have been evacuated to Uummannaq, the eleventh-largest town in Greenland (see picture below).

2
This Temblor map shows the location of the M=4.1 earthquake on the western coast of Greenland. Despite its small magnitude, the quake caused a landslide, which triggered a tsunami that killed four people.

While this earthquake appears to be tectonic in nature, according to Professor Meredith Nettles of the Lamont-Doherty Earth Observatory at Columbia University, Greenland also experiences what are known as glacial earthquakes. Glacial earthquakes are a relatively new class of seismic event, and are often linked to the calving of large outlet glaciers. While this type of event has also been observed in Antarctica, the majority have been recorded off the coast of Greenland, and show a strong seasonality, with most of them occurring late in the summer.

3
This photo shows Uummannaq, the eleventh-largest town in Greenland. This is where 40 people were evacuated to from Nuugaatsiaq following the tsunami over the weekend.

Because glacial earthquakes have a different mechanism than normal earthquakes, standard earthquake monitoring techniques cannot be used to detect them, which explains why they were not known about until 2003. Additionally, while a tectonic M=5 quake typically lasts about 2 seconds, a comparable M=5 glacial earthquake can emit long-period (great than 30 seconds) seismic waves. It is because of this, that they have a separate classification.

In order for a glacial earthquake to occur, a large-scale calving event has to take place. When a glacier calves, there is both a sudden change in glacial mass and motion. While a glacier is technically a river of ice, meaning it slowly flows downhill, when a large calving event take place, there is a brief period when horizontal motion reverses. Couple this with a downward deflection of the glaciers terminus, which causes a upward force on earth’s surface, and you have the recipe for a glacial earthquake. These earthquakes tend to be M=4.6-5.1.

4
This figure, from Nettles and Ekstrom, 2010 shows 252 glacial earthquakes in Greenland from 1993–2008, detected and located using the surface-wave detection
algorithm.

Despite the fact that this tectonic quake was by no means large, it was big enough to trigger a massive landslide into the ocean, and the ensuing displacement of water was enough to form a tsunami that devastated parts of Nuugaatsiag. Prof. Nettles said to us, “The M=4.1 earthquake does not explain the large, long-period (slow) seismic signal detected by seismometers around the globe. The long-period signal appears to be due to a landslide, and the time of the long-period signal is later than the time of the high-frequency (earthquake) signal. It is possible the earthquake triggered the landslide.” What this means is that both the earthquake and landslide generated seismic signals, but that the earthquake signal appeared first, suggesting the quake triggered the slide. The video below shows a view of the landslide, while the photos show the landslide and the devastation caused by the tsunami. In response to this event, and the risk of aftershocks, people have been advised to stay away from the coastline.

5
This picture, taken by the Arctic Command shows part of the landslide that triggered the deadly tsunami.

6
This photo shows damage in Nuugaatsiaq, following a deadly tsunami over the weekend. (Photo from: Olina Angie K Nielsen via Facebook)

References
Geological Survey of Denmark and Greenland (GEUS)

Meredith Nettles and Goran Ekstrom, Glacial Earthquakes in Greenland and Antarctica, Annu. Rev. Earth Planet. Sci. 2010. 38:467–91, doi: 10.1146/annurev-earth-040809-152414

T. Murray, M. Nettles, N. Selmes, L. M. Cathles, J. C. Burton, T. D. James, S. Edwards, I. Martin, T. O’Farrell, R. Aspey, I. Rutt, T. Baugé, Reverse glacier motion during iceberg calving and the cause of glacial earthquakes, sciencemag.org/content/early/recent / 25 June 2015 / Page 1 / 10.1126/science.aab0460

2015 Washington Post article by Chris Mooney titled “Giant earthquakes are shaking Greenland — and scientists just figured out the disturbing reason why” – Link

2015 NPR article titled “Study Reveals What Happens During A ‘Glacial Earthquake” – Link

See the full article here .

Please help promote STEM in your local schools.

STEM Icon

Stem Education Coalition

You can help many citizen scientists in detecting earthquakes and getting the data to emergency services people in affected area.
QCN bloc

Quake-Catcher Network

The Quake-Catcher Network is a collaborative initiative for developing the world’s largest, low-cost strong-motion seismic network by utilizing sensors in and attached to internet-connected computers. With your help, the Quake-Catcher Network can provide better understanding of earthquakes, give early warning to schools, emergency response systems, and others. The Quake-Catcher Network also provides educational software designed to help teach about earthquakes and earthquake hazards.

After almost eight years at Stanford, and a year at CalTech, the QCN project is moving to the University of Southern California Dept. of Earth Sciences. QCN will be sponsored by the Incorporated Research Institutions for Seismology (IRIS) and the Southern California Earthquake Center (SCEC).

The Quake-Catcher Network is a distributed computing network that links volunteer hosted computers into a real-time motion sensing network. QCN is one of many scientific computing projects that runs on the world-renowned distributed computing platform Berkeley Open Infrastructure for Network Computing (BOINC).

BOINCLarge

BOINC WallPaper

The volunteer computers monitor vibrational sensors called MEMS accelerometers, and digitally transmit “triggers” to QCN’s servers whenever strong new motions are observed. QCN’s servers sift through these signals, and determine which ones represent earthquakes, and which ones represent cultural noise (like doors slamming, or trucks driving by).

There are two categories of sensors used by QCN: 1) internal mobile device sensors, and 2) external USB sensors.

Mobile Devices: MEMS sensors are often included in laptops, games, cell phones, and other electronic devices for hardware protection, navigation, and game control. When these devices are still and connected to QCN, QCN software monitors the internal accelerometer for strong new shaking. Unfortunately, these devices are rarely secured to the floor, so they may bounce around when a large earthquake occurs. While this is less than ideal for characterizing the regional ground shaking, many such sensors can still provide useful information about earthquake locations and magnitudes.

USB Sensors: MEMS sensors can be mounted to the floor and connected to a desktop computer via a USB cable. These sensors have several advantages over mobile device sensors. 1) By mounting them to the floor, they measure more reliable shaking than mobile devices. 2) These sensors typically have lower noise and better resolution of 3D motion. 3) Desktops are often left on and do not move. 4) The USB sensor is physically removed from the game, phone, or laptop, so human interaction with the device doesn’t reduce the sensors’ performance. 5) USB sensors can be aligned to North, so we know what direction the horizontal “X” and “Y” axes correspond to.

If you are a science teacher at a K-12 school, please apply for a free USB sensor and accompanying QCN software. QCN has been able to purchase sensors to donate to schools in need. If you are interested in donating to the program or requesting a sensor, click here.

BOINC is a leader in the field(s) of Distributed Computing, Grid Computing and Citizen Cyberscience.BOINC is more properly the Berkeley Open Infrastructure for Network Computing, developed at UC Berkeley.

Earthquake safety is a responsibility shared by billions worldwide. The Quake-Catcher Network (QCN) provides software so that individuals can join together to improve earthquake monitoring, earthquake awareness, and the science of earthquakes. The Quake-Catcher Network (QCN) links existing networked laptops and desktops in hopes to form the worlds largest strong-motion seismic network.

Below, the QCN Quake Catcher Network map
QCN Quake Catcher Network map