Mandalay (Myanmar) earthquake

[pres...@aees.org.au]

Dear AEES members,

 

See attached for an interesting summary of the recent magnitude 7.7 Mandalay earthquake by AEES Past President Paul Somerville.

 

For comparison, the typical design scenario for Australia with a Z factor of 0.08 is broadly associated with a peak ground velocity of 60 mm/s, and this event had peak ground velocity recordings of 1000 mm/s and higher.

 

Kind regards,

Scott

 

--

Scott Menegon PhD CPEng

President

Australian Earthquake Engineering Society Inc.

www.aees.org.au | pres...@aees.org.au | +61 400 709 335

 

 

[Adam Pascale]

I’m sure most of you have probably seen this by now, but here is a link to the video of the first time an active rupture has been caught on video. It is high quality security camera footage of the Sagaing Fault rupturing during the M7.7 Myanmar earthquake from a solar farm in Tha Pyay Wa.

The P-waves are seen arriving at about the 10-second point in the video, with a little horizontal shaking opening the gate a few seconds later, and then at the 15-second mark the entire portion of land on the other side of the fence (right half of the screen) slides several metres horizontally. Wild.

If you rewatch it and look at the top left of the screen, you can see the surface rupturing from the building in the distance towards the gate, with the transmission tower in the top right of the screen then collapsing. Amazing stuff. 

<image001.png>

 

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<2025-March-25-Mw-7.7-Mandalay-Myanmar-Earthquake-2.pdf>

[Paul Somerville]

Adam

Thanks for sharing this - it is a much clearer version of the video than the one I saw.

From the shadow of the gate at about noon it is evident that the camera is looking south

toward the sun. The epicentre was about 100 km north of here, behind the camera, so

the rupture would have propagated from right to left in this view.  It would have propagated

at about 3km/sec, and I am not sure that a camera or a human eye could capture that.

What you do see is the "rise time," the duration of slip on the fault once the rupture front

has arrived. If you look at the solar panel stand just inside the right side of the frame of the gate, 

it moves to the right by about 3 metres in about 1 second and ends up aligned with the left 

edge of the right frame of the gate.  Usually the slip velocity is about 1 m/sec, but this looks like 3 m/sec.

The earthquake was strike slip so that checks out - the other side of the fault moved to the right. 

The fault is evidently just outside the yard - you can see the road on the right side just on the other

side of the fence moving past the fence. 

A good way to see the total slip on the fault (although backwards) is to look at the image in

its stationary state (with the red circle and arrow inside it). That shows the end state of the view.

As soon as you click the arrow, it jumps back to the starting state.

Rupture velocity and slip velocity can be thought of this way.  If you are in a sports stadium

and people start making waves, the wave can propagate at quite high speed around the

stadium.  As the wave (rupture front) reaches each spectator, they start to move (stand up)

and then sit down in a process that may take a second or two, and by the time they

have sat down the wave may be on the other side of the stadium.

See the attached briefing

Paul

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[da...@earthquake.net.au]

The earthquake insights site has a very long post on this video, pulling it apart pixel by pixel.

 

https://earthquakeinsights.substack.com/

 

Regards

David

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