GEOL 240 MIDTERM #2 STUDY GUIDE - A MY Sept 30 Active...

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AMY Sept 30 Active Faults of the Los Angeles Region: “Other Big Ones” Beneath Our Feet Rates of Pacific-North America relative plate motion / distribution of this total rate amongst various fault systems that make up the plate boundary: · Cape Mendocino: where San Andreas goes off shore and then into Mendocino fracture zone · Relative motion of pacific plate is 5 cm (50 mm) per year · 90% plus culminated on fault systems · San Andreas system- 70% of the 5 cm per year total relative plate motion between north American and pacific plate (aka 35 mm) o Accommodated in central California · Eastern Ca sheer zone- 10 mm (1 cm) per year o Along western range of basin and range SAF 1857 & 1906 eqs: 1857 Fort Tejon · Magnitude 7.9 · Ruptured down to San Bernardino stopped about 1 km short of I-15 · About 350 km long · Average slip of 5 m · Not too many causalities · Reruptured part of December 8, 1812 earthquake o Different end points o Pallet Creek- less than 45 years between earthquake 1906 San Francisco Earthquake · 450 km of northern San Andreas · Right lateral slip · Average slip about 5 meters · Magnitude 7.9 · Conspiracy theory- earthquake downplayed and fire blamed for most of damage done by both natural disasters o Done because they did not want people to move away- very astute of them o And they still want people to want to move to SF o No one at the time had earthquake insurance- there was fire insurance, but none for earthquakes o Death toll: 5,000 to 10,000 people · Reason SF wasn’t level was because there was no source directivity- energy is not going to be propagated in all directions · There was no chance to develop directivity pulse creeping section of SAF:
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Creeping Section of Faults · In San Andreas fault · There are certain parts of the system that are not locked close- instead of bending rocks and storing energy, it is effectively lubricated by some talc like mineral- so slippery that they cannot stay locked · Serpentine- old oceanic crust (lithosphere) got exposed to water at spreading ridge and it was caught up in coast ranges in CA · Only example on continental faults where the creep rate equals the slip rate · Fault creeping: sliding past each other semi- continuously major splays of SAF in northern and southern CA/ origin  of SF Bay ?: (I think  this   is what  it’s  referring  to. .  idk  for  sure  though)   San Francisco bay: mostly a mud flat San Andreas run off shore in Bay Area · Slip rate of 20 mm year Northern California faults of San Andreas fault system · Hayward fault o Second of main faults in nor cal o Slip rate of 10 mm year · Calaveras fault o Slip rate of about 5 mm year preliminary discussion of source directivity and basin amplification (I  don’t  have   this  stated  explicitly  in my  notes,  so if someone  does  then  please  add  it!)   relocation of December 8, 1812 eq: December 8, 1812 Estimated magnitude 7.5 · Damage all over Southern California
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This note was uploaded on 02/19/2011 for the course GEOL 240 taught by Professor Sammis during the Fall '08 term at USC.

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GEOL 240 MIDTERM #2 STUDY GUIDE - A MY Sept 30 Active...

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