geology questn #1: why is there no peninsula where the San Andreas fault enters the Pacific at Daly City, CA?
Aug 31, 2009
in
Earthquake Questions
If, for millions of years, the west side of the San Andreas fault has been moving northwesterly to the east side, should not the mountainous coastal land mass south of where the fault enters the sea (at Daly City) have formed a peninsula by now? (PS: for whoever answers this question, I will appreciate
your looking at my Geology question # 2, relative to the Alburqueque rift valley also). Thanks.
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2 comments
qfl247 on August 31, 2009 at 4:42 pm
There is nothing that will necessarily form a peninsula there just because of the San Andreas. The reason is the fault is not a simple straight line. It is more of a zone, it has moves and turns, and locally there is uplift and depressions. This is why there is no clear landform directly moving into the sea, it does not move so smoothly.
Also, each earthquake event that created an mass of land poking into the bay would be subject to massive erosion for two reasons. Firstly, the fault itself has a gouge zone almost a mile wide in places, so any land moved by the fault near the fault is very weak due to the fault. Secondly, this new peninsula would be subject to local currents that exist in the bay and formed the bay, and this new ‘jetty’ could be easily eroded.
tonalc1 on August 31, 2009 at 4:42 pm
The land as it is now is the result of the land creep. More accurate to ask might be, what did the Northern California coastline look like millions of years ago?