How to assess an earthquake risk?
Ali Oncel
Rapid Earthquake
Risk Assessment
Source
Parameters
Shake Maps
Aftershocks
Slip/Stress
Model
USGS
World
USGS
Shake
IRIS Seismic
Monitor
CALTEC
Figure 1
OUTLINE:
•
Earthquake Magnitude
–
Types of magnitude
•
•
Earthquake Depth
–
How deep it is?
•
•
Shallow or Deep
Type of faulting
–
–
Vertical
•
Thrust Fault
•
Normal Fault
Lateral
•
•
ML, MB, MS, MW
Strike-slip
Slip and Stress Model
–
Slip
•
Asperity
First Draft
I am motivated to write up on possible ways to perform a quick assessment of an
earthquake and possible risk since a larger earthquake of M6.5 occurred in west coast of
Canada today. First, we need to understand the size of an earthquake, which is defined,
based on the types of earthquake waves, e.g. surface wave magnitude or body wave
magnitude, but moment magnitude solution is critical to explain an earthquake since it
based on more physical parameters such as rupture length and fault slip. Secondly, we
have to look at the earthquake depth to estimate how it would cause a risk, because
shallow depth earthquake cause more damage. For example, most earthquakes in
Japan are larger in magnitude, but they do not cause damage since they are deeper
more than 40 km. Next step, we need to assess the type of faulting, because it shows a
mechanism of the earthquake which is critical to estimate apparent stress distribution.
Finally, we need to understand possibility of earthquake interaction or fault coupling by
examining the pre-existence faults around the earthquake.
As a seismologist, I am motivated to write up on a model of Rapid Earthquake Risk
Assessment since larger earthquakes can cause an emergency problem for helping those
people in need. Luckily, the larger earthquake of M6.5 occurred today in west coast of
Canada was large enough, which showed an earthquake hazard was present in Canada,
but the risk due to earthquake was limited since it occurred in the sea, which was away
from the populated areas. But, we know that the earthquakes in Canada are always
possible through the populated areas.
Final Draft
In this short paper, I propose a preliminary model (Figure 1), which can be used
to fulfill a rapid earthquake assessment since I am motivated to study on it following a
larger earthquake of M6.5 that occurred today in the west coast of Canada. First, we
need to estimate basic parameters of an earthquake, i.e. magnitude, depth and
epicentre, but their estimates are always a matter of discussion due to complexity of the
rupturing process. Hence, robust estimate for earthquake depth is not given in the
areas in which the crustal thickness is not studied well. A moment magnitude provides
accurate estimate of an earthquake since its calculation is based on a physics of the
earthquake rupture, e.g, rupture length and fault slip.
Finally, both the size of
earthquake and its location are a factor affecting earthquake risk.
Secondly, we need to use a Shake Map technology for assessing rapid
earthquake damage.
It gives size variation of the caused damage by ground
amplification that is measured by strong-motion seismometer. If there is no deployed
strong motion seismometer around the city, we have nothing to do much in order to
ground responses in a city. Thus, deploying a seismic network will allow to use Shake
Map technology to make a priority list for sending help teams to people in need.
Next step, we need to prepare aftershock forecasting map since aftershocks
occurs frequently following an earthquake, and we could show the location of the
aftershocks as it is performed like weather estimate, but it requires also deployment a
seismic network. It is important to evacuate the areas to mitigate the damage.
Final step, earthquake slip that shows slip maps, where an area of larger slip is
asperity that is patch of fault causing an earthquake, onto an earthquake fault can be
used to model a distribution of the fault stress. Because, a larger earthquake can load
stress onto another fault; therefore, it might advance time of earthquake on the closer
faults. It will help us to predict the location of the next earthquake. Consequently,
rapid estimate earthquake risk requires a great investment to deploy seismic networks
for both monitoring aftershocks and measuring ground motion. However, a national
earthquake rapid assessment team needs organizing to cooperate for accomplishing
different tasks as shown in the model.
Final Revised Draft:
In this short paper, I propose a
preliminary model that can be used to fulfill a
rapid earthquake assessment (Fig.1). The
motivation of this paper is due to a recent
larger earthquake of M6.5 that occurred
today in the west coast of Canada (Fig.2).
First, we need to estimate basic parameters Figure 2: The earthquake location, Nov 17, 2009,
of an earthquake, i.e. magnitude, depth and is shown. The map is taken from Globe and Mail
epicentre, because the size changes of which
controls the damage of one earthquake. However, their accuracy is always a matter of
discussion, due to complexity of the rupturing process, among the scientists. Because,
earthquake depth is not estimated accurately in the areas in which the thickness of
seismogenic layer, brittle part of the crust, is not studied well. A moment magnitude
provides a better estimate of the released energy
since its calculation is based on a physics of the
earthquake rupture, e.g, area of the earthquake
fault surface, fault slip and the rigidity.
Consequently, both the size of earthquake and its
location are a factor affecting the estimate of the
earthquake risk.
Secondly, we need to use a Shake Map
technology for an immediate assessment of
earthquake damage. It gives size variation of the
caused damage by ground amplification that is
measured by strong-motion seismometer and
scaled from I to X as shown in Fig.3. The meaning
of the map, we consider sending help first to areas
with higher ground motion.
It is a good
technology for emergency caused by a large
earthquake, but nothing to do for emergency
people if there is no deployed seismic network
around the city. Thus, deploying a seismic
network is critical to save lives after a devastating
earthquake.
Next step, we need to prepare aftershock
forecasting map since aftershocks occurs
frequently following an earthquake, and we could
predict the location of the aftershocks as it is
performed like weather estimate, but it requires
also deployment a seismic network.
It is
Figure 3: An example of the shake map for
southern California. The map is taken from the
USGS site.
Figure 4.
Real-time estimation of the
aftershocks are shown for California, from
USGS.
important to evacuate the areas to mitigate the damage.
Final step, earthquake slip that shows slip maps, where an area of larger slip is
asperity that is patch of fault causing an earthquake, onto an earthquake fault can be
used to model a distribution of the fault stress. Because, a larger earthquake can load
stress onto another fault; therefore, it might advance time of earthquake on the closer
faults. It will help us to predict the location of the next earthquake. Consequently,
rapid estimate earthquake risk requires a great investment to deploy seismic networks
for both monitoring aftershocks and measuring ground motion. However, a national
earthquake rapid assessment team needs organizing to cooperate for accomplishing
different tasks as shown in the model.