Term
| what three peices of geologic evidence do we need to define a fault avoidance zone? |
|
Definition
the three peices of geologic evidence we need to define a fault avoidance zone are:
1. where the fault is
2. how much it tends to slip
3. recurrence interval of quakes |
|
|
Term
| what is the goal of a risk-based planning approach? |
|
Definition
| the goal of a risk-based planning approach is to use geologic data to evaluate the risk of proposed development |
|
|
Term
| what are the six steps in the risk-based planning approach? |
|
Definition
Six steps in the risk-based planning approach
1. find the faults in the zone you are managing
2. create a fault aviodance zone
3. determine the "nature" of the quake hazard, which breaks down into recurrence interval and fault complexity/type
4. evaluate the vulnerability of proposed development. what qualities of the development will affect the risk?
5. treat (reduce) the risk. Figure out how much action is appropriate, set the regulatory measures
6. monitor/review |
|
|
Term
| why is a straightforward geologic analysis not always appropriate for finding recurrence interval? |
|
Definition
| a straightforward geologic anaylsis may assume the past is like the future, but earthquakes cluster. We can't always assume past ruptures are indicative of future ruptures, and we can't assume calculated recurrence intervals are correct |
|
|
Term
| what is suprising about a plot of fault length vs displacement? |
|
Definition
| a plot of fault length versus displacement shows us that longer faults don't slip as much as you'd think they would. This ceiling is due to long faults reaching the brittle-ductile transition. faults can't move into the brittle-ductile transition |
|
|
Term
| what makes finding the magnitude of a complex fault more involved? |
|
Definition
| the find the magnitude of a complex fault, you need to look at many multiple faults that slipped in tandem |
|
|
Term
| why was it complicated to find the magnitude of the darfield quake? |
|
Definition
| the reason it was complicated to find the magnitude of the darfield quake was that the darfield quake was a complex fault that involved many surface faults slipping in tandem |
|
|
Term
| draw a plot of slip versus depth of the faults that went off during the darfield quake |
|
Definition
|
|
Term
what are 4 qualities of the geologic system that affect whether displacement along one fault will set the next one off
|
|
Definition
these are 4 qualities of a geologic system that determine if a rupturing fault will set others around it off
1. what geologic features are around/in between the faults? the way these features respond to stress, shaking, and other forces will affect how energy moves around the system.
2. the geometry of multiple faults. are the all facing the same direction, etc
3. changes in stress/strain due to displacement as rupture occurs. The energy profile of the system changes dramatically over the course of a quake
4. how far the faults are from one another |
|
|
Term
| what is the threshold distance between faults at which there is no chance of one triggering another? |
|
Definition
| the threshold distance between faults at which there is no chance of one triggering another is 5 km. If two faults are 5+ km away, they won't trigger one another |
|
|
Term
|
Definition
| the key observation here is the critical distance at which faults won't trigger one another. It's 5 km in this data set |
|
|
Term
| right after a quake, this distinct process allows the rupture zone to increase in strength. As the rupture zone increases in strength, stress builds up in fault while decreasing in the surrounding region |
|
Definition
| right after a quake, the fault zone begins to anneal. This process strengthens the fault zone and allows stress to be concentratred in the fault area. |
|
|
Term
| describe every step in the seismic cycle |
|
Definition
the sesimic cycle is:
1. stress builds up
2. stress exceeds fictional force, quake occurs
3. rupture zones anneals and quickly gets stronger, allowing for step 1 again |
|
|
Term
| what is the key question for geologists regarding fault linkage |
|
Definition
| the key question for geologists regarding fault linkage is "will one fault set the next off" |
|
|
Term
| why doesn't fault length affect stress drop? |
|
Definition
| stress drop is per unit area, so the size of the fault doesn't matter |
|
|
Term
| why do smaller faults see bigger stress drops? |
|
Definition
| smaller faults see bigger stress drops because they don't enter into the brittle-ductile transformation zone, which doesn't fault the way bedrock does |
|
|
Term
| how does size relate to stress drop of faults? |
|
Definition
| smaller faults see bigger stress drops |
|
|
Term
| how do we know fault zones anneal? |
|
Definition
| we can see fault zones anneal as the low-velocity zone along the rupture path gets smaller and smaller |
|
|
Term
| what would you study specifically post-quake with geophysical tools |
|
Definition
| you can use geophysics to watch the low velocity zone along the rupture path caused by fractures anneal as liquid rock pours in and recrystallizes |
|
|
