The Penasco cluster is named for the city of Puerto Peñasco at the
northern end of the Gulf of California, Mexico. It covers appoximately
the northernmost quarter of the length of the Gulf. Earthquakes range up
to mid-5 in magnitude. Because of the geometry of seismicity in the
middle of the Gulf and seismograph stations on either coast, few events
have near-source observations for depth control. As might be expected
for an immature oceanic spreading system the crustal velocity structure
(25 km thick) is thinner than normal continental crust but thicker than
true oceanic crust. All events have depth constraint, mainly from
local-distance readings, but some from teleseismic depth phases and
waveform modeling. The distribution of seismograph stations provides
good azimuthal coverage and the location calibration is quite robust.
