By now, many of you have probably heard the reports about yesterday
morning's temblor centered in the Hercules area (M3.4 at 10:21am PDT). I
experienced that quake while I was working at my computer. And like many of
the other felt reports, it was a quick, single and sudden motion; much like
a truck slamming into the side of the building. It was so like many other
Hayward fault quakes which prompted me to accurately guess the magnitude of
the event and its most likely source. No magical powers or anything like
that - it's only due to my experience with having lived in the proximity of
the Hayward fault for many years. I quickly checked the USGS online maps and
sure enough, the temblor was shown. One interesting thing I noted in regards
to this quake's epicenter is that it didn't line up along the northern
extension of the Hayward fault. My question is regarding the dip in the
Hayward Fault plane in this particular area. Is there a dip? How much? The
epicenter appears to be some 5-6 miles east-northeast of the surface trace
of the fault. Mind you, I am aware that not all quakes line up on the shown
fault traces due to the fault's dip angle but I was not aware of any dip, to
that degree in this area. This quake had a depth of 5.6 km.

Does anyone have any comments?


 

Kareem Lanier
Heyjoojoo.com


 

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