This article provides some excellent descriptions of & graphics about the #TurkeySyriaEarthquake.

To clarify, however, the "fissure opened up by the quake" near Tepehan village is not a fault scarp but a landslide.

1/

reuters.com/graphics/TURKE…
Maps comparing the scale of the faults to other land masses can be startling - at ~250 km, the M7.8 seems very long!

That's the reality of large earthquakes. The longest known earthquake rupture was the 2004 M9.1 earthquake: 1500 km.

3/

tectonics.caltech.edu/outreach/highl…
In my head I have a catalog of nightmare scenarios on faults that I know will host large earthquakes.

I don't know when they will happen.

I don't know if I will be around to see them.

It's really hard to talk to people about them.

4/
People don't want to listen. They have more urgent problems than something that might not happen for 100 years.

Until it happens.

How do we make progress?

5/end

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More from @JudithGeology

Feb 18
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.

1/
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.

2/

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.

3/
Read 6 tweets
Feb 15
How do we measure shaking in an earthquake?

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.

Here is a map of shaking in the #TurkeySyriaEarthquake

1/
Mostly, shaking is decribed by its "intensity". Intensities communicate what the shaking "feels like" and how it could affect structures in the area.

Explore intensities in the Feb 6 M7.8 earthquake here:

earthquake.usgs.gov/earthquakes/ev…

2/
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.

en.wikipedia.org/wiki/Accelerog…

3/
Read 18 tweets
Feb 13
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!

1/
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

2/
The hazard of the East Anatolian Fault is well known, and represented by this seismic hazard map:

3/ Image
Read 4 tweets
Feb 12
A startling video of more slope failure caused by the Turkey earthquakes.

Here, the built up material below a road gave way - highlighting how engineering failures are not limited to buildings.

1/
Lateral spreading below roads has been seen before - here is an example from the 2018 M7 earthquake in Alaska, described by @davepetley.

Humans create this hazard: anthropogenic materials are failing.

blogs.agu.org/landslideblog/…

2/
The first earthquake in Turkey occurred at 4:17 AM local time, with few people on the roads.

But roads are critical in the aftermath of an earthquake, as aid workers try to reach impacted people across the region.

Like buildings, they too must be built to resist shaking.

3/
Read 4 tweets
Feb 11
This rift is not a fault, but was still caused by Monday's earthquakes. It is the headscarp of a landslide.

Landslides and rock falls are common triggered hazards in earthquakes.

1/
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

2/
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.

3/
Read 7 tweets
Feb 10
Now more than ever, this article is extremely sobering.

There is an "earthquake gap" south of Istanbul: an active fault, primed to rupture.

1/

nature.com/articles/ncomm…
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.

2/ Image
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.

3/ Image
Read 4 tweets

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