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Introduction to Seismology
Seismic Hazard Analysis 1(pp.455-460)
Department of Earth SciencesKFUPM
Ali [email protected].
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There are several online catalogs of earthquakes. In this exercise, you will need to access one of these. For earthquakes any place in the world, a good place to start is: http://wwwneic.cr.usgs.gov/neis/epic/epic.html A catalog of focal mechanisms (CMT Solutions) is at the Harvard seismology site: http://www.seismology.harvard.edu/ You will need to use an Excel spreadsheet to solve some of these problems.
Homework on Earthquake Search due May, 3
1. How many earthquakes occurred for the Saudi Arabia and vicinity since 1973
a) with magnitude 6.0 or larger.
b) with magnitude 5.0 or larger.
c) with magnitude 4.0 or larger.2. Present your data, giving the average number of earthquakes per year and establish Log N= a – b M.3. By consulting the Harvard catalog of moment tensors, for the largest of the events in this region, infer the main tectonic process in this region. Explain the reasoning behind your response.In
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33° E 60° E
10° N
37°N
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Oncel, 2006
Depth=0-20kmTime Interval: 1973-2005
Log (N)= 8.06 – 1.12 M
Frequency-Magnitude Model
Mc=4.6
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Oncel, 2006
Zoning: Spatial mapping of the variations in seismicity or earthquake strong ground motion (and identification of similar zones)
Parameters to map:Occurrence of damaging earthquakes (Mallett 1858)Number of felt earthquakes (e.g. Balloré 1896)Io
Macrozoning on the regional scale
Microzoning takes into account localised conditions e.g. rock and soil type
Recall: Seismic ZonationIn
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Microzoning for Saudi Arabia
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Regionsa-value b-value Mmax Area (Km2)1 4.66 0.67 7 320582 4.93 0.67 7.4 430503 850324 986185 366386 4.77 0.82 5.8 674767 496148 4.67 0.7 6.7 780099 4495810 5.14 0.75 6.9 11235811 3.08 0.55 5.6 4495812 3.62 0.5 7.2 6732313 4.71 0.67 7 33585114 3.21 0.59 5.4 34351615 2.34 0.59 4.6 37973016 3.64 0.66 5.5 53317417 4.02 0.65 6.2 25779818 6.83 0.94 7.2 16064419 5.84 0.84 6.9 14863620 40863621 2.42 0.51 4.8 40358022 7.15 1 7.2 14009623 3.35 0.59 5.7 32406024 6.06 0.85 7.1 20958525 4.35 0.71 6.1 238136
Al-Amri (2005)
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b-value
0.4
0.8
1.2
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
b-value
Mmax4
5
6
7
8
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
Mmax
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Oncel, 2006 after Al-Amri, 2005
What about the Mmax?
Magnitude prediction equations
• Best known: Wells and Coppersmith (1994).
– Distributed to the class.
– Recommendation: read the article, and learn
how to use these relations.
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See pp. 437 of Bullen and Bolt
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Adams, 2006Al-Amri, 2005
Macro-/Microzoning for Saudi Arabia
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Abdalla and Al- Homoud (2004)
Al-Amri (2005)
Compared Models of Seismic HazardIn
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5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9
2 3
2 4
2 5
2 6
2 7
2 8
2 9
3 0In
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5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9
2 3
2 4
2 5
2 6
2 7
2 8
2 9
3 0
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Abdalla and Al- Homoud (2004)
Case Work: Eastern ArabiaIn
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Abdalla and Al- Homoud (2004)
Seismic Zones on Eastern Arabia In
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Seismic Sources for Eastern Arabia
Abdalla and Al- Homoud (2004)Intr
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Maximum Expected Earthquakes for Seismic Sources
Abdalla and Al- Homoud (2004)Intr
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Hazard Parameters for Seismic Sources of Eastern Arabia
Could you write Magnitude-Frequency Relations for Regions 1 and 2?
Log N= 10.17 – 1.22 M Region 1
Log N= 6.99 - 0.94 M Region 2
What is the number of M7 for regions 1 and 2?
Abdalla and Al- Homoud (2004)
1008-2002
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What is the Frequency?
Log (N/Tobs)= 10.17 – 1.22 M Region 1
Log (N/Tobs)= 6.99 - 0.94 M Region 2
Tobs= 995 yearsWhat is the number of M7 for regions 1 and 2?
(N/Tobs)= 10 10.17-1.22*7
(N/Tobs)= 10 6.99-0.94*7
0.043 for Region 1
0.03 for Region 2
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What is the recurrence period for M7 events?
T(1)= 1/ (N/Tobs)=
T(2)=1/ (N/Tobs)=
23.33 yrs387.10 yrs
Which of those regions has large hazard?
Region 1? Or Region 2?
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What is the Recurrence Time?
Probability is given by formula as:
P(t)= 1-e-t/T
Recall T is recurrence time while t is years
Then calculate the M=7 probability for 30 years?
P(t)= 0.72 or % 72 for Region 1
P(t)= 0.07 or % 7 for Region 2
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What is the Earthquake Probability?
