Santa Cruz (western Pacific) Earthquake Swarm!

The past couple of days have brought us a series of large magnitude strike-slip earthquakes along a plate boundary between the Solomon Trench and the New Hebrides Trench. I posted about the first earthquake here and here. This swarm of earthquakes, along with the other recent seismic activity along this system, supports the hypothesis that this is a strike-slip plate boundary (nor a subduction zone as plotted on some maps).
Here is a map that I put together. I plot the epicenters of the earthquakes, along with the moment tensors for the three largest magnitude earthquakes. I also place a transparent focal mechanism over the swarm, showing the sense of motion for this plate boundary fault. Technically, transform plate boundaries are strike-slip (shear) plate boundary fault systems that connect spreading ridges. SO, I would like to call this a transform plate boundary fault system, but need to see if it really satisfies the definition that people use… I’ll get back to us on this…
I also note that these three largest earthquakes happen in a time order from east to west, unzipping the fault over three +- days. I label them in order (1, 2, 3) and place an orange arrow depicting this temporal relation). Very cool!

    Here are the USGS web pages for the three largest earthquakes in this series:

  • 2015.05.20 Mw 6.8
  • 2015.05.22 Mw 6.9
  • 2015.05.22 Mw 6.8

Here is an updated regional map with all of the epicenters from this swarm plotted. Below I link to an earlier map with more notations on it.

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