8.7 earthquake in Sumatra

Another great earthquake has struck Sumatra, a bit south of the 26 December shock. Preliminary magnitude is 8.7 (upgraded from 8.2), and its tectonic setting and mechanism make it possibly another tsunami-generating event, though there was no official tsunami warning because no agency covers that region. Large waves did not materialize. More details as the day goes on. The US Geological Survey has a dedicated page for this event. The focal mechanism is pure thrust, directed NE-SW. This is somewhat counterclockwise from the orientation of December's quake, suggesting (and I am not a seismologist) that any tsunami would have bypassed India this time. The absence of a tsunami goes to show how irregularly they occur, even when a large seismic event seems like it would trigger one.