Hi I'm Ali Sealander with you UTD GeoNews and I'm here to tell you about a strong
earthquake that shook Idaho recently. Idaho's a beautiful mountainous state in
the northwestern US. It's something of a frontier state; large in size and small
in population. Idaho is known for its year-round outdoor sports and for
growing potatoes. More recently Idaho was in the news
because of a strong earthquake that shook it a little before 6:00 in the
afternoon on March 31st, 2020. Fortunately, no one was killed or injured and there
was very little damage. The earthquake had a magnitude of 6.5 with an epicenter
in the mountains 45 miles west of a small town named Challis. It was the
second largest earthquake in Idaho history and occurred in the most
seismically active part of Idaho. This is near where the state's biggest
earthquake occurred in 1983, the magnitude 6.9 Borah earthquake. The 1983
earthquake caused a visible scarp, but no scarp is yet reported for the 2020
earthquake, although the region is currently
blanketed in snow. The nearby mountain town of Stanley has urged people to stay
away in order to protect it 65 residents from potential coronavirus exposure, so
this has made it hard for scientists to see what has happened there. What else do
we know about the 2020 Idaho earthquake? According to Glenn Thackeray at Idaho
State University, "The March 31st earthquake looks like he was on a fault
that actually cuts across the end of the Sawtooth Fault." The Sawtooth fault is
fairly large and active in this area. The USGS reports that the earthquake was
caused by about one meter, or three feet, of movement on a fault at about 20
kilometers, or 12 miles, deep in the crust. The USGS also calculates focal mechanism
solutions which can be used to constrain what kind of faulting happened and the
orientation of the fault which caused the earthquake. Their calculations show
that this earthquake was caused by strike-slip faulting, where two crustal
blocks slide past each other. This could either be a right-lateral slip on an
east-west trending fault or left-lateral slip on a north-south
fault. Because the March 31st earthquake seems to lie on a north-south fault we
suspect that a left-lateral slip fault caused the earthquake. Let's compare the
focal mechanisms for four recent U.S. earthquakes in California, Utah, Texas, and
Idaho. The strike-slip nature of the Idaho earthquake is similar to that of
the July 4th, 2019, magnitude 7.1, Ridgecrest, California earthquake, but the
earthquakes that occurred in March 2020 in both magna Utah and Mentone Texas
have focal mechanism solutions that point instead to normal faulting, where the
crust is stretched apart. Both strike-slip and normal faulting is
expected in the region around the Basin Range province of the western United
States where stretching and sliding has been going on for millions of years.
Things are getting back to normal in Idaho earthquake wise. Although there
have been almost three hundred small aftershocks in Idaho since the March
31st earthquake. Further research is needed before we know more about what
caused this interesting earthquake and what is shaking in the seismically active
central Idaho region. I'm Ali Sealander and I'll see you on the next GeoNews