{"id":6962,"date":"2018-01-19T19:06:41","date_gmt":"2018-01-20T03:06:41","guid":{"rendered":"http:\/\/earthjay.com\/?p=6962"},"modified":"2018-01-19T19:06:41","modified_gmt":"2018-01-20T03:06:41","slug":"earthquake-report-gulf-of-california","status":"publish","type":"post","link":"https:\/\/earthjay.com\/?p=6962","title":{"rendered":"Earthquake Report: Gulf of California"},"content":{"rendered":"

Today we had an earthquake with magnitude M 6.3 in the Gulf of California (GOC). The GOC is formed by transtension (extension along a strike-slip fault system) along the North-America-Pacific plate boundary. Transtension happens when the plate motion across a fault is not oriented parallel to the fault. This non-optimal relation (plate motion vs fault direction) can generally happen as a result of (1) a bending fault or (2) due to stepped offsets of the fault. The dextral (right-lateral) strike-slip faults here make “right-steps” and pull apart basins form in these locations.
\nThe strike-slip faults are offset by oceanic spreading ridges. These spreading ridges are connected the East Pacific Rise to the south (and the Juan de Fuca Ridge and Gorda Rise to the north, via the San Andreas fault).
\nThe geology of this region is much more complicated than this, but this is a good place to start when trying to understand the tectonics here. This M 6.3 earthquake happened on the southern boundary of the Guamas Basin, one of these pull apart basins.
\nSo far there has been a single aftershock (M 4.5).
\nThis M 6.3 earthquake<\/a> appears to be pretty typical of this part of the Gulf. There have been several M 6 earthquakes in the last century. There have been a couple M 7 earthquakes, to the north.<\/p>\n

Below is my interpretive poster for this earthquake<\/font><\/h2>\n

I plot the seismicity from the past month, with color representing depth and diameter representing magnitude (see legend). I include earthquake epicenters from 1918-2018 with magnitudes M \u2265 6.5.
\nI plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange) for the M 6.3 earthquakes, in addition to some relevant historic earthquakes.
\nI labeled the pull-apart basins in cyan and the faults in light orange. CdBF – C. de Ballenas fault; GF – Guaymas fault; CF – Carmen fault; FF – Farallon fault; PF – Pescadero fault; AF – Alcaron fault; AR – Alcaron Ridge (from Arag\u00f3n-Arreola, M. and Mart\u00edn-Barajas, A., 2007).<\/p>\n