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.
M = 7.1
Table 1. Earthquake Chronology Hokey Poky fault, Oregon, USA. Earthquake Number Site ASite BSite CSite D Age (yrs AD)RI Age (yrs AD)RI Age (yrs AD)RI Age (yrs AD)RI Average RI this year2013 next expected EQ time span 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.