Harrat Lunayyir and the Saudi Arabian earthquake swarm

I have finally gotten together enough to create a Google Earth image (below) of the location of the Saudi Arabian earthquakes and their depths/magnitudes. I only have the data from the USGS earthquake list, but it is very illuminating:

i-12fbbc67ce47dad0d5684d2bb20ae622-Saudi Earthquakes2_sm.jpg

Harrat Lunayyir volcano in western Saudi Arabia from Google Earth with the current earthquakes shown on the image. Image courtesy of Google, earthquake data from the USGS. Click here to see a larger version.

The earthquakes look like this (all times are Universal Time):
Date Time Mag. Depth
5/17 19:50 M4.6 10 km
5/19 06:38 M4.9 10 km
5/19 16:54 M4.9 10 km
5/19 17:35 M5.7 7.6 km
5/19 19:57 M4.6 10 km
5/19 20:35 M4.6 10 km

There are likely a bunch of smaller events going on as well, but this is all the data I have on hand. Overall, the depth over the last few days doesn't seem to be significantly changing (within the error of the depth estimates). I'm still not sure how this shows that magma is moving (according to some of the early quotes from Saudi Arabian officials)

UPDATE 11:45 AM Pacific
: Just as I posted this, I saw this: Saudi Arabian officials have extended the emergency zone out 40 km from the earthquakes. No clear indication whether they are doing this out of fear of the seismicity or potential volcanic activity, but it definitely shows increasing concern.

Harrat Lunayyir is a lava field about which we honestly don't know too much. It is relatively small compared to other lava fields in western Saudi Arabia, but some flows made it to the Red Sea, a distance of 50 km / 35 miles! In terms of previous eruptions, the only datum is a potential eruption around 1000 A.D., but beyond that, not too much. If you look at the image (above), you can see the dark black basaltic (or basanite) lava flows. You can also see the image is pockmocked with reddish dots - these are oxidized cinder cones, a very common feature of lava fields.

The fact that these earthquakes all seem to be centered under a known lava field should be a sign of concern. Without confirmation of some of the eyewitness accounts, there is still a chance that these might not be related to the lava field, but until we can get more information, we're still left to speculate.

More like this

Erik; roughly, what are the dimensions of the image in km?

Mike Don - That is an excellent question ... and a mistake that I would have taken points off from my students if they forgot the map scale (doh!) Anyway, from right to left, it is ~98 km / 60 miles across in this image. Sorry!

Wish I knew more seismology :o( The pattern doesn't SEEM like tectonic quakes; don't they usually tend to have a major shock followed by lesser aftershocks, rather than a series at similar magnitude? They're mostly at the same depth, which doesn't suggest magma rising (although the lesser events could, possibly, tell a different tale). Relief of crustal stress because of the mass of the volcanic structure? Hardly..this is no Fuji or Shasta.

Could it be magma movement with a large lateral component..i.e injection of a sill?

I continue to believe that magma injecton could be a consequence of the tectonic activity wich drives the molten rocks uplift by strong changes in the stress field.

from a1saudiarabia.com: eruption now likely : "The warning was issued following the discovery of dangerous gases and unusually hot air and water in wells as the frequency of tremors increased in Al-Ais. A Civil Defense source said the discoveries suggested a volcanic eruption was likely" ??


All evacuated from Al-Eis
http://tinyurl.com/pr9cno (Saudi Gazette)

By robert somerville (not verified) on 21 May 2009 #permalink

Shame on you, you did take points off my sketches for no scale bar!

But also, I'm curious about the extent of the lava flows. 50 km strikes me as a long way for a basalt flow to travel. Is it just that there's sufficient slope (900 m/50 km) to get the basalt to the sea, or is there something else I'm missing?

Robert Somerville's grab bag tectonic theory (original ??) for western Saudi Arabia ...

the magma coming up from the red sea spreading center is too buoyant (hot) to be subducted in the Persian/Arabian gulf .. it is accumulating under Western Saudi Arabia causing uplift and rifting/faulting/flood basaltic flows ...

By robert somerville (not verified) on 21 May 2009 #permalink

Hey Anne! My guess is that if the lavas are true basalts or basanites, you don't need much of a slope from the source to make it to the see, especially if there is the potential for crusting over of the flows to form temporary lava tube system like we've seen in Hawai'i (or are suggested for the Columbia River Basalts). However, that is still a pretty long way for any lava flow to make it!