Answer doesnt need to be complex, im not even a geology major Name: Course/Secti

Question

Answer doesnt need to be complex, im not even a geology major

Name: Course/Section: Date: 1 is a digital hillshade map of the area around Wallacc Creck in central California along the San Andreas Faulo centered around 35.2 San Andreas Fault North American Plate side Wallace Creek Pacific Plate side Wallace Creek San Andreas Fault North Figure A16.4.1 The most recent large earthquake along this part of the San Andreas Fault occurred in 1857 when about 9.5 m of slip occurred there during a magnitude 7.9 earthquakc 1. Use a pencil to trace the fault between the two arrows on Fig. A16.4.1 as carefully as you can, 2. Describe the visual evidence in the hillshade image that you used to decide where to draw the trace of the fault. 3. Recall that geologists use a pair of arrows along the trace of a strike-slip fault to indicate the direction of relative motion across the fault. Interpret the sense of displacement across the San Andreas Fault (i.e., whether its motion is right lateral or left lateral), and use a pencil to draw paired arrows along the fault trace Wallace Creek is an ephemeral stream that is dry most of the time but flows during wet seasons. Flow is from the North rican side toward the Pacific side. Points a, b, and c on the Pacific Plate side mark points where Wallace Creek has across the fault at various times in the past from point d on the North American Plate side. Geologists Kerry Sieh flowed and Richard channel a - 13,000 yr; channel b-10,000 yr; and channel c 3700 yr 1. What is the length in mm on Fig. A16.4.1 that corresponds to 200 m of distance in the Wallace Creek area? Jahns interpreted the approximate ages of initial development of the Wallace Creek channels as follows: mim 423

Explanation / Answer

Ana A1) The fault is traced on the map as a black line. It is based on the depression trend on the map.

Ans A2) The shifting of the stream channels are the most important visual aid where we can clearly see the fault along which the stream

is displaced.

Ans A3) If we stand on the Pacific plate side facing the North American plate we can clearly see that the streams have shifted to the right on the North American plate, therefore this is a right lateral displacement. The relevant arrows are plotted on the map.

Ans B1) Given scale on the map is

2.5cm=0.2km

25mm=200m

Ans B2) We know that

25mm on map =200m on ground

25mm on map =200,000 mm on ground

1mm on map =200,000/25 mm on ground

1:8000

Ans B3)

Ans B4)

Ans C)

Calculated displacement rate =0.041 m/yr

Total displacement rate= 0.051 m/yr

therefore percentage displacement by San Andreas Fault = (0.041/0.051)*100

=80%

Ans D) The displacement between the two plates needs to accommodated by the different fault system. We can look for segments on the San Andreas fault where the displacement is much higher. We can look for other smaller faults where there are displacements going on by carrying out similar exercises. The

distance on map Scale distance on field a to b 12mm 1:8000 96000mm b to c 35mm 1:8000 280000mm c to d 20mm 1:8000 160000mm a to d 67mm 1:8000 536000mm

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