Seismic Activity

Question 1

(1) Tear fault - the San Andreas Fault - Where does the San Andreas fault lie?

Answer 1

At the junction of the Pacific and North American plates.

Question 2

(1) Tear fault - the San Andreas Fault - what causes earthquakes along the fault?

Answer 2

The Pacific plate (on the west) moves northwestward relative to the North American plate (on the east).

Question 3

(1) Tear fault - the San Andreas Fault - the San Andreas is the what?

Answer 3

The ‘master’ fault of an intricate fault network that cuts through rocks of the California coastal region.

Question 4

(1) Tear fault - the San Andreas Fault - the entire San Andreas fault system is what?

Answer 4

More than 800 miles long and extends to depths of at least 10 miles within the earth.

Question 5

(1) Tear fault - the San Andreas Fault - in detail…..

Answer 5

The fault is a complex zone of crushed and broken rock from a few hundred feet to a mile wide. Many smaller faults branch from and join the San Andreas fault zone.

Question 6

(2) A Right-Lateral Strike-Slip Fault Motion - some great blocks of rock have what?

Answer 6

Moved laterally long distances over geological time

Question 7

(2) A Right-Lateral Strike-Slip Fault Motion - landscape features such as…..

Answer 7

Streams and sedimentary deposits of all ages are offset along the fault, with youngest rocks offset less than older rocks.

Question 8

(2) A Right-Lateral Strike-Slip Fault Motion - the amount and rate of offset along the fault is what?

Answer 8

Not consistent because it’s consists of a complex system of parallel and interconnecting faults.

Question 9

(2) A Right-Lateral Strike-Slip Fault Motion - some sections of the fault are what?

Answer 9

Constantly creeping along, whereas other sections are locked during periods between episodic large earthquakes.

Question 10

(2) A Right-Lateral Strike-Slip Fault Motion - in general what?

Answer 10

The western Pacific plate is moving northward at about two inches per year relative to the North American plate.

Question 11

(3) A Right-Lateral Strike-Slip Fault Motion - another component is what?

Answer 11

The compressional forces generated across the fault as the two plates grind against each other.

Question 12

(3) A Right-Lateral Strike-Slip Fault Motion - this compression helped what?

Answer 12

Produce the Pacific coast mountain ranges along the fault system through California.

Question 13

(3) A Right-Lateral Strike-Slip Fault Motion - what has been produced by the San Andreas fault?

Answer 13

A linear trough of lakes, bays and valleys.

Question 14

(3) A Right-Lateral Strike-Slip Fault Motion - This landscape can be what?

Answer 14

Difficult to associate with seismic activity but does include distinctive landforms such as long straight escarpments, narrow ridges, and small undrained ponds formed by the settling of small blocks within the zone.

Question 15

(3) A Right-Lateral Strike-Slip Fault Motion - many stream channels what?

Answer 15

Characteristically jag sharply to the right where they cross the fault

Question 16

(4) A Right-Lateral Strike-Slip Fault Motion - sudden offset…..

Answer 16

That Initiates a great earthquake occurs on only one section of the fault at a time.

Question 17

(4) A Right-Lateral Strike-Slip Fault Motion - total offset…..

Answer 17

Accumulates through time in an uneven fashion, primarily by movement on first one, and then another section of the fault.

Question 18

(4) A Right-Lateral Strike-Slip Fault Motion - studies of a segment of the fault between…..

Answer 18

Tejon Pass and Salton Sea revealed geologically similar terrain on opposite sides of the fault now separated by 150miles.

Question 19

(4) A Right-Lateral Strike-Slip Fault Motion - some crustal blocks may have what?

Answer 19

Moved through more than 20 degrees of latitude. This represents a rate of drift of as much as 2 inches per year.

Question 20

(5) EVALUATION - seismic activity produces what?

Answer 20

More subtle landscapes that can often be viewed more clearly from the air

Question 21

(5) EVALUATION - the linear arrangement of…..

Answer 21

Lakes, bays and valleys formed by the San Andreas fault and the linear trough it has produced are striking.

Question 22

(5) EVALUATION - viewed from the ground however…..

Answer 22

The features contrast markedly with the landforms of extrusive and intrinsic activity.

Question 23

(5) EVALUATION - however, compressional seismic activity has what?

Answer 23

Also contributed to more visually striking and easily distinguishable features in this location with the Pacific coastal mountain ranges located to the east of the coastal plain.

Question 24

(5) EVALUATION - when considered over what?

Answer 24

Longer geological timescales the amount of movement that has occurred is staggering.

Question 25

(5) EVALUATION - estimations…..

Answer 25

Of the total accumulated displacement from earthquakes and creep is at least 350 miles along the San Andreas fault since it came into being about 15-20 million years ago.