Jason R. Patton @earthjay@qoto.org

@SakuRainbow @earthjay Interestingly, you can look at different solutions for the the same earthquake (M7.3 #Tonga shallow #earthquake of 11 Oct), depending on the inversion method: https://earthquake.usgs.gov/earthquakes/eventpage/us7000ip0l/moment-tensor.

@SakuRainbow @earthjay Actually, the rounded parts show that the moment tensor is not 100% consistent with pure slip on a planar fault ("pure double couple"). But maybe 10% is unexplained. The rest can be due to 1/ uncertainty in the inversion, 2/ actual complexity of the rupture (multiple faults activated, roughness of the fault...) or 3/ volume change (e.g. when magma is involved). #SCARDEC assumes a pure fault plane, whereas #USGS leaves more freedom to inversion. See https://pubs.er.usgs.gov/publication/70020193

@SakuRainbow @earthjay This #USGS educational material may also help : https://www.usgs.gov/programs/earthquake-hazards/focal-mechanisms-or-beachballs#:~:text=A%20focal%20mechanism%2C%20or%20%22beachball,of%20the%20fault%20that%20slipped. 👍

@SakuRainbow @earthjay Here is the same earthquake analysed by #Geoscope. The 1st image shows the focal mechanism. This is a stereographic projection of 4 quarter-spaces: ◻️ is the region where the rupture radiates tensional ⏪⏩ waves, ◼️ is where compressional waves ⏩⏪ are radiated. What you need to care about is the limit between ◻️ and ◼️: it corresponds to the two *possible* planes, which are perpendicular ❌. Both planes are depicted in 2nd figure

In 2015, a M7.8 earthquake occurred in Nepal. This video from IRIS (narrated by me) explains this #earthquake, as well as the seismic hazard and risk for #Nepal and #India.

https://m.youtube.com/watch?v=5VjaSFEf4BU&feature=youtu.be

For my PhD I worked on understanding the uplift of the Southwestern margin of the Tibetan Plateau, focusing on the Karakoram and Longmu Co fault systems and surround mountain ranges.

These are right and left lateral strike slip fault systems (respectively) that are helping to accommodate the motion between #India and Eurasia.

Here’s an open source paper that gives some background. https://pubs.geoscienceworld.org/gsa/geosphere/article/14/4/1837/532684/Structural-relationship-between-the-Karakoram-and