# Shared Flashcard Set

## Details

Lecture 14
Seismic Hazard assessment
38
Geology
05/26/2015

Term
 when we are looking at buildings, our focus is on what measure of earthquake intensity?
Definition
 when we are looking at buildings, we care about the intensity of shaking. Specfically, the amount of energy transferred at different frequencies
Term
 building code for non-critical vs critical infrastructure related to earthquakes
Definition
 building code for non-critical buildings: they must to able to survive 1 in 475 year shaking for critical buildings (post-disaster importance, like shelters and hospitals): they must be able to survive 1 in 2,500 year shaking
Term
 if you are in a tall building, you hope the shaking is at ____ frequency
Definition
 if you are in a tall building, you hope the shaking is at shorter frequency
Term
 [image]
Definition
 the key observation from that graph is that there is more accleration on the high frequency/low period side of the curve
Term
 how do soft layers in the ground respond to shaking?
Definition
 soft layers in the ground amplify shaking, but they eat some high frequency waves
Term
 how do harder layers in the ground react to shaking?
Definition
 harder layers in the ground allow waves to travel further, and don't absorb any high frequency waves
Term
 [image]
Definition
 the takeaway from this graph is that accleration was greater than the 2,500 year return at most frequencies. the fact that people walked out of buildings meant to withstand 475 year shaking is really fortunate
Term
 does the current building code take post-event fuctionality into account?
Definition
 the current building code doesn't take post-event functionality into account. buildings up to code can stay upright during shaking, but must be torn down afterward. Post-event functionality means they can be repaired after shaking
Term
 there was talk of changing the Z factor in the building code, (higher Z code=more resilient to shaking) from .22-.3 or 3.5  how much would this bring up construction costs? (give a range)
Definition
 [image]
Term
 what two peices of information do we use to figure out how many blind faults there are?
Definition
 to figure out how many blind faults there are, we start by connecting magnitude to chance of surface rupture. using the G-R law, we can solve for many faults there are that move but don't have a signal at the surface
Term
 why do fewer magnitude 7 earthquakes in NZ cause surface ruptures? 2 reasons
Definition
 2 reasons why an above average % of magnitude 7 earthquakes come from blind faults in NZ 1. NZ geology close to surface has more weak rocks and soft layers that simply shift and absorb the energy instead of bringing rupture to surface 2. NZ is a subduction zone, so many earthquakes originate deeper
Term
 how do we find blind faults we haven't mapped yet?
Definition
 to find blind faults we haven't mapped, we use the G-R law. log(displacement) vs number of events is a straight line
Term
 Sesimic hazard model takes these two factors into account
Definition
 the seismic hazard model is a function of siesmic source data and the expected site response
Term
 what three things go into figuring out seismic source data?
Definition
 the three things that go into figuring out seismic source data are: 1. distributed seismicity 2. mapped faults 3. Floating sources, which are faults we haven't mapped but we know are there b/c of the G-R law
Term
 expected site response takes what three things into acount?
Definition
 expected site response takes into account these three things 1. where site is compared to rupture 2. site's vulnerability 3. attenuation, which is weaking of signal over time
Term
 the sesimic hazard model must take into account the distribution of how different sites will response to a certain shaking intensity at ____
Definition
 the sesimic hazard model takes into account how different sites will response to a certain level of critical shaking at different frequencies
Term
 knowing the magnitudes and recurrance intervals of faults isn't enough to create meaningful seismic source data. other information do you need?
Definition
 knowing the magnitudes and recurrance intervals of faults isn't enough to create useful seismic source data. To get risk of anaylsis from magnitudes and recurrence intervals you need to use the G-R law to find a magnitude-frequency relationship
Term
 the goal of the seismic hazard model is to produce what?
Definition
 the goal of the siesmic hazard model is to produce a  temporal distribution of how a range of sites will react to various shaking intensities at various frequencies.
Term
 sesimic source data relies on what three peices of informatuion?
Definition
 seismic source data relies on surface rupture length, subsurface rupture length, and moment magnitude (Mw)
Term
 what does the term "characteristic earthquakes" refer too?
Definition
 the term characteristic earthquake refers to faults that produce earthquakes at regular recurrence interval, and where displacement is similar every event
Term
 what does the christchurch hazard deaggregation plot tell us?
Definition
 the christchurch hazard deaggregation plot shows us that a lot of hazard in CC comes from blind faults. If a magnitude 6 earthquake hits CC, there's a 50% chance it came from a blind fault. If a mag 9 quake hits CC, there is a 90% chance it came from a blind fault
Term
 what is the goal of fault-based seismic hazard analysis?
Definition
 the goal of fault-based siesmic hazard analysis is to take geolgic data and turn it into a recurrance interval and slip rate
Term
 what case study did we look at that involved segmented faults slipping in tandem?
Definition
 the darfield earthquake involved 7 faults slipping in tandem
Term
 what is seismogenic thickness?
Definition
 seismogenic thickness is the distance from the deepest part of the rupture to the surface
Term
 what is down dip width?
Definition
 down dip width is the width of a fault measured in the down-dip direction
Term
 what is seismic moment?
Definition
 seismic moment is a measure of the strength of a quake based on area of fault rupture, average amount of displacement, and force required to overcome friction
Term
 what is the measure of a width of a fault measured in the down dip direction?
Definition
 the measure of a width of a fault measured in the down dip direction is called down dip width
Term
 what is do we call the depth of the deepest part of a rupture?
Definition
 the depth of the deepest part of the rupture is seismogenic thickness
Term
 this quality of a quake is a function of it's rupture area, average displacement, and the frictional force overcome?
Definition
 seismic moment is a measure of a quake's size based on the area of fault rupture, the average amount of displacement, and the frictional force that was overcome
Term
 how do we get the surface slip rate of a fault?
Definition
 the surface slip rate of a fault is based on geological observations combined with paleoseismology
Term
 how do find sesimogenic thickness?
Definition
 to find seismogenic thickess, use a combination of geophysical observations and studying earthquake distributions
Term
 how do we calculate down dip width?
Definition
 down dip width is a function of surface dip and siesmogenic thickness. DDW is the down dip width, which is the width of a fault in the down dip direction
Term
 how do you find the fault plane area?
Definition
 the fault plane area is DDW*length of rupture
Term
 how does one derive MO and Mw when doing a fault-based seismic hazard analysis?
Definition
 MO and MW are dependent on fault area, slip, and sesimic moment
Term
 how do we find subsurface single event displacement (SED) and subsurface slip rate (SR)?
Definition
 we use surface SED and surface SR to find subsurface SEB and subsurface SR
Term
 what are the nine steps in fault-based sesimic hazard analysis?
Definition
 the steps in fault-based seismic hazard analysis 1. map the fault 2. see if the fault is segmented, see if it moves in tandem with other faults. Remeber that the darfield quake invoved 7 faults slipping together  3. Geology/paleoseismology step. Find the surface slip rate (SR) 4. geophysics/quake distribution analysis step. find the sesimogenic thickness 5. use seismogenic thickness and dip at surface to find down dip width 6 use down dip width and length to find fault plane area (DDW*L=fault plane area) 7. find Mw and MO with fault area, slip, and seismic moment  8. use surface SED and RL to find subsurface SED and RL 9. use subsurface RL to find recurrance interval
Term
 3 qualities of good earthquake forecasting
Definition
 good earthquake forecasting is 1. publicly availible 2. continously updated 3. provides information at different timescales
Term
 draw a profile of a fault indicating down dip width, hanging wall, and footwall
Definition
 [image]
Supporting users have an ad free experience!