Since we don’t know where the next large earthquake is going to strike, installing good seismic networks everywhere is important, especially places prone to earthquakes.
In a world divided by national borders, and covered 71% by oceans, this is a work in progress.
Installing a station is just the first step. Without regular maintenance, it will last only a few years. Vandalism, flooding, insects, battery failure, mice, overgrowth of solar panels, and even grizzlies can damage equipment.
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And then there’s the question of how you get the data. Will you visit the station every 6 months and download it, or set up satellite telemetry? For rapid data use, the latter is necessary - but not cheap.
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Magnitude measures the size of the quake - but how much shaking you feel depends on how close you are to the fault, the materials under your feet, and more.
Intensities are calculated by measuring shaking with seismometers. When shaking is very strong, only certain kinds of seismometers - those designed to record strong ground motions - will work: more sensitive ones clip, or go off scale.
For almost every large earthquake, I could truthfully state:
"This earthquake was larger than any ever observed on this fault."
The Earth is slow! The biggest earthquakes occur with 100s of years in between.
That's why geologists don't rely only on the historical record!
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To understand the hazard of a fault, geologists look at:
-Long-term deformation of the ground
-Offsets recorded by sediments
-Computer models of slip
-Deformation recorded by GPS across the region
-Microseismicity
-Models of shallow sediments, which can amplify shaking
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The hazard of the East Anatolian Fault is well known, and represented by this seismic hazard map:
Here you can see satellite images of this area before and after the earthquake. The block is a triangular region between two gulleys.
Shaking destabilized the slope, and a block about 150x250 m2 slid ~40 m downslope.
Credit: Dr. Kyle Bradley
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The blocks in the valley exposed in the video show the layered sediments. It is likely that a layer of tilted sediment is weak - perhaps clay or a similar material - and slid.
That layer may extend over a wider area, putting more regions at risk.
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With the last two large events on this fault segment occurring in 1509 and 1766, and a suggested recurrence interval of ~200-250 years, this part of the fault may produce an earthquake at any time.
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The fault segments highlighted here could produce ~M7. But Monday's earthquakes in southern Turkey ruptured multiple segments in a complex series, increasing the resulting magnitude. That kind of multi-fault rupture could happen here too.