1. HOW ARE we “BLIND” TO some of our faults?
HANNAH SHAMLOO

2. Blind thrust faults
Some faults do not break through the surface anywhere along their length
-some faults are not easy to locate or study, often go unnoticed for many years
-sometimes faults are ‘buried’ by deposition of material atop the surface trace during the period between surface ruptures
-other times, faults simply do not reach the surface or diffuse into folds beneath surface
-existence of this type of “blind” fault is usually expressed at surface as chain of hills or by folding of local rock formations, which is what we have here

3. Puente hills thrust fault
Recently discovered, 1999
Los Angeles Basin
Runs about 40 km
Three segments
Slip rate 5mm/year
4 Major E.Q.’s last 11,000 years
-so we are aware that Northridge Earthquake in 1994 was produced by blind thrust faulting
-but I would like to focus on a fault system that is less well known, but going to be very damaging in the future
-because blind faults aren’t easily discovered, the puente hills fault system was more recently discovered in 1999 through a borehole
-it is an active fault located in los angeles basin
-runs about 40 km in three north-dipping sections from the Puente Hills region in the SE to just south of Griffith Park the NW, overlain by folds
-Los Angeles, Santa Fe Springs, and Coyote Hills
-slip rate of 4.5-5mm/year or .20inch/year
-large earthquakes on the fault are infrequent, but if it were to happen, it would be make a substantial impact
-a simultaneous rupture of all three PHT segments would produce a Mw 7.1 earthquake.

4. Compared to Northridge…
DANGER
Compared to Northridge…
Northridge’s E.Q. directed strongest shaking towards N to sparsely populated mountains
PHT fault focuses its shaking toward downtown LA
LA Basin amplifies shaking
15x stronger energy release
-it has had 4 large earthquakes in the last 11,00 years from M
-this fault focuses its shaking toward downtown LA, and ground motions from this event might be severely damaging
-this fault’s shape and direction make it different from the one that triggered the Northridge earthquake in 1994
-while Northridge's quake directed it’s strongest shaking towards N to sparsely populated mountains
-The frequency of a major rupture in the Puente Hills Fault is on the order of once per several thousand years.
-This frequency of occurrence is relatively rare compared to the San Andreas fault
-the highest magnitude in that range would be about fifteen times stronger than the Northridge Earthquake in terms of energy release.
-the shaking would be much greater too because of the unconsolidated sediment
-as tom jordan said, “northridge would look like a walk in the park”
Viz Credits: Amit Chourasia 

5. REFERENCES
Marquis, John. "New Study Reveals The Behavior Of The Puente Hills Thrust Fault." New Study Reveals The Behavior Of The Puente Hills Thrust Fault. Southern California Earthquake Center, 4 Apr Web. 18 June 2013.
Maugh II, Thomas H. (May 26, 2005). "Big Fault Under L.A. Could Be Devastating". Los Angeles Times 26 May Web. 18 Jan. 2013
Shaw, John H., Andreas Plesch, James F. Dolan, Thomas L. Pratt, and Patricia Fore. "Puente Hills Blind-Thrust System, Los Angeles, California." Thesis. N.d. Bulletin of the Seismological Society of America, 16 Nov Web. 18 Jan