[Shake-dev] oddities of the 4.2 Ocotillo Wells ShakeMap

[Jack Boatwright]

Bruce,

Your ShakeMap for the recent M4.2 Ocotillo Wells event could use some
intervention.  At the moment, the peak intensity is carried by a pair of
false stations about 8 km to the north of the epicenter.  The closest
station is 5375, which is 6.4 km to the south.  It appears that your
pthresh = 10 km, so that the program is not putting a false station at the
epicenter.

A related difficulty is the PGA of 1.1%g at EML, 74 km off to the
southwest.  This PGA is probably a glitch that escaped your glitch-catcher.
(I can't look at your waveforms to check.)  In any case, your PGA bias is
0.22, a jump higher than the PGV bias of 0.08.  But it could be the large
GM at SAL which is controlling the bias.

In any case, I suggest that you either increase cthresh so that the pair of
false stations to the north are excluded, or decrease pthresh so that the
epicentral false station is included.  Also, you should check the recording
at EML, and possibly choose to suppress that station.

But I don't know what it will look like.  I'm only bringing this to your
attention because you have stated in the past that you don't want ShakeMap
introducing false maxima.

					take care,         Jack