The Earth Story

INSAR

Radar is an extremely useful tool for monitoring changes in the Earth’s surface. Interferometric synthetic aperture radar, or INSAR, can accurately measure tiny changes in the Earth’s surface.

Radar waves pass through Earth’s atmosphere and will bounce off land surfaces. Radar is a form of light - electromagnetic radiation - so like light it is a type of wave with a frequency/wavelength. When radar bounces from the surface to a spacecraft, it arrives back at a specific point in each wave. It's difficult to turn small changes in wavelength from pixel to pixel into any useful information since they’re a function of many properties of the surface, but if 2 images taken close together in time are subtracted from each other, tiny changes from one frame to another stand out. Those tiny changes in the wavelength of the returning energy are reflected in changes in the colors on an INSAR interferogram like this one. As the wavelength of the returning energy changes, it either builds constructively on the waves in the previous pass or interferes destructively.

INSAR is a tool that can show changes in the Earth’s surface from one scene to the next – changes like deformation in a volcano or motion from an earthquake. If 2 closely timed radar images are available, earthquake motions can be understood and volcanic eruption warnings can be given, but doing so requires a satellite built to do the measurement.

Previous satellites could do these measurements, but they weren’t built to do rapid overpasses. A few years ago, the European Space Agency launched its Sentinel-1A satellite (http://on.fb.me/1B1f6Jj), the first in its next-generation series of Earth-observing spacecraft. That satellite carries radar specifically designed for INSAR – it will be able to image every point on Earth’s surface every 12 days.

This INSAR image shows ground deformation in an earthquake in Oaxaca , Mexico last year. The ground moved by a maximum  of about 40 centimeters in this earthquake, so each of the contours of color represents about 3 centimeters of ground motion. The points marked show estimates of the earthquake epicenter based on seismic measurements made by the USGS and Mexican seismic networks; clearly based on this image, the nearby seismic instruments from the Mexican seismic network produced a more precise estimate of the epicenter location.

-JBB

Image credit: EOS/ESA/NASA https://disasters.nasa.gov/oaxaca-mexico-earthquake-2018/insar-map-deformation-due-m72-oaxaca-earthquake https://eos.org/project-updates/earthquake-monitoring-gets-boost-new-satellite

On Wednesday, two powerful earthquakes struck Italy in the region close to the site of the deadly earthquake earlier this year. The first quake was smaller, while the second quake was among the most powerful quakes to hit Italy during the history of seismic records. So far casualties have not been reported - it is possible that both the remote location of these quakes and the fact that the first quake could have caused people to evacuate before the larger quake hit could have worked together to limit casualties. However, those reports are early and things may change as the sun comes up on Thursday. This video captures the collapse of a structure during the larger of the two quakes.

This video is a neat view - this shows earthquake epicenters (the place on the Earth’s surface above an earthquake) during the long-lived Bárðarbunga/Holuhraun eruption last year. Especially cool to watch the early part.

Earthquakes start near the Bárðarbunga crater as magma is moving into the system then they take off to the northeast and form a linear path towards the site where the actual eruption would take place. A linear, vertical path taken by magma is known as a dike - they commonly form in systems like Iceland where the crust is being pulled apart. You can literally use these earthquakes to watch a dike grow and a volcano become active.

Study Reveals Some Clues to the Texas Earthquake Mystery

Last month, a small earthquake rumbled through Irving, TX (http://on.fb.me/1zIl4t4)—a bit odd for a location that is nowhere near a plate boundary. In fact, the north Texas area in general has had over 120 earthquakes since 2008…very odd indeed. The mysterious nature of these quakes caused many to point fingers at the fracking industry…but was that really what caused it? The United States Geological Survey and Southern Methodist University jumped in further to figure it out.

Their recently published study reveals that the Irving earthquakes occurred along a north-northeast line from Irving, TX to West Dallas, TX, which indicates there is a fault there. The earthquakes occurred at depths of 4.5 – 7 km, in the crystalline basement rock, below any sedimentary deposits. Most of the earthquakes have been small—no greater than magnitude 4—but noticeable up to 25 miles away from the epicenter.

The information is helpful for determining seismic risk, but it does not tell us everything. There are two abandoned wells and one wastewater injection site near Irving, but the most recent earthquakes are probably too deep to have been caused by fracking.

Could fracking still have caused the other Texas quakes? Or are they also related to faults? What would have caused this previously unknown fault to move? For now, these remain unanswered questions.

-CM

For the full report: http://bit.ly/1L3xges

Photo credit: http://bit.ly/15yFaz3

Storytelling Tradition Saved Lives in Boxing Day Tsunami Memorials to those who died in the tsunami on Indonesia’s Banda Aceh do more than offer remembrance; they also provide an education tool to teach school children about tsunamis and to recognize the warning signs. After the Boxing Day earthquake, many people went to the beaches when the waters receded instead of going to higher ground, which cost them their lives. It is a much different story on Indonesia’s island of Simeulue, where 7 people died out of a population of around 70,000. Simeulue is located just 50 kilometers from the epicenter where the 9.2 magnitude earthquake hit. The island received no warning that the tsunami was coming. Simeulue has suffered through earthquakes and tsunamis in the past, and an oral tradition called “smong” developed. Grandparents in particular teach their grandchildren the smong which concludes with, “If a strong tremor occurs, and if the sea withdraws soon after, run to the hills, for the sea will soon rush ashore.” The people on Simeulue’s coast remembered this lesson and ran to the island’s hills, thereby saving their lives. It is hoped that educating school children in Banda Aceh will ensure that they too will know what to do if a tsunami ever happens again. - RE Photo Credit: Tsunami damage in Sumatra by U.S. Navy photo by Photographer's Mate 2nd Class Philip A. McDaniel http://bit.ly/16QHYrM Read More:  http://www.bbc.com/news/magazine-30542317?OCID=fbasia http://unesdoc.unesco.org/images/0018/001831/183133e.pdf