Geology 15 Mid Term II Review

Focal mechanisms are diagrams made from first motion seismologic records that show the possible motion on a fault, and the possible sense of motion on that fault. There are two possible fault planes for each focal mechanism.

http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php

M = 7.1

Table 1. Earthquake Chronology Hokey Poky fault, Oregon, USA.

Earthquake Number

Site A Site B Site C Site D

Age (yrs AD) RI

Age (yrs AD) RI

Age (yrs AD) RI

Age (yrs AD) RI

1 1857286

185745

185745

1812108

2 1571187

1812265

1812127

1704145

3 1384107

1547187

1685149

1559122

4 1277199

1360276

153649

1437124

5 1078479

108417

1487127

1313140

6 599

1067111

136096

1173242

7 956

1141264

148931

8 842

781116

100 9

764119

1016166

10 645

850

69 11

781

59 12

722

25 13

697

63 14

634

101 15

533

Average RI 252 135 95 147

this year 2013 2013 2013 2013

next expected EQ 2109 1992 1952 1959time span 1258 1212 1324 881

Is the average Recurrence Interval about the same for each site? NO

What can the Recurrence Interval say about this fault?(1) earthquakes did not rupture through each site for each earthquake for some reason. (2) the time between earthquakes varies so that we can interpret this fault to be uncharacteristic and unpredictable. (3) the RI at site C is much shorter than the RI of A. (4) the RI at sites B and D are intermediate compared to sites A and C.

Which sites (A, B, C, or D) are more “due” for an earthquake?Adding the average RI to the age of the most recent earthquake gives us an estimate for when the next earthquake might occur ("next expected"). The first expected earthquake was at site C, then site D, site B, and lastly site A.

Is the average Recurrence Interval about the same for each site? NO

What can the Recurrence Interval say about this fault?(1) earthquakes did not rupture through each site for each earthquake for some reason. (2) the time between earthquakes varies so that we can interpret this fault to be uncharacteristic and unpredictable. (3) the RI at site C is much shorter than the RI of A. (4) the RI at sites B and D are intermediate compared to sites A and C. (5) the earthquakes that occur at all sites probably represent larger earthquakes. (6) the fault has different places that are more resistant to slipping (more friction) and this may make the fault slip at different rates.Which sites (A, B, C, or D) are more “due” for an earthquake?Adding the average RI to the age of the most recent earthquake gives us an estimate for when the next earthquake might occur ("next expected"). The first expected earthquake was at site C, then site D, site B, and lastly site A.