@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

@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 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 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.