Transcript Climate change and Urban Vulnerability in Africa

Climate change and Urban
Vulnerability in Africa
Assessing vulnerability of urban systems,
population and goods in relation to natural and
man-made disasters in Africa
“Training on the job” Course on Hazards, Risk and
(Bayesian) multi-risk assessement
Napoli, 24.10.2011 – 11.11.2011
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Fatemeh Jalayer
1
Earth Structure
Crust: The uppermost 5-70 km of the earth. There are
two types of crust: continental and oceanic.
Continental crust ranges from 10-70 km thick and has
a composition approximating that of granite. Oceanic
crust, on the other hand, is approximately 5 km thick
and has a composition similar to basalt, making it
significantly denser than continental crust.
Mantle: The middle portion of the interior of the
earth, starting below the crust at 5-70 km below the
earth’s surface and continuing to a depth of 2900 km.
Core The innermost layer of the earth, which starts at
~2900 km depth. The core is composed mainly of iron
and consists of a molten outer core and a solid inner
core.
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Plate Tectonics
Subduction zones
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Mid-Ocean ridges
Slide 3
Plate Tectonics
Map showing earthquakes from 2003-2011 with magnitude greater than 3. Colors indicate
depth of hypocenter, or origin of the earthquake: red is 0-33 km, yellow is 33-100 km, green
is 100-400 km, and blue is >400 km depth. Data are from the Advanced National Seismic
System.
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Plate Tectonics
Map showing volcanoes that have been active in the last 10,000 years. Colored triangles
indicate different volcano types: red triangles are primarily calderas, green triangles are
stratovolcanoes, blue triangles are shield volcanoes and fissure vents. Data are from the
Smithsonian Institution, Global Volcanism Program.
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Plate Tectonics
Divergent boundaries
Cross-section of the Mid-Atlantic Ridge near latitude 14° S. Blue triangle represents the location of fissure
volcanoes. Colored circles represent earthquakes, color-coded by depth
Transform boundaries
Cross-section of the San Andreas Fault in
California near latitude 36° N. Colored circles
represent earthquakes, color-coded by depth
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Plate Tectonics
Convergent boundaries
Oceanic meets continental
Oceanic meets more oceanic
Cross-section of the South American subduction zone
near latitude 22° S. Green triangles represent the
locations of stratovolcanoes. Colored circles represent
earthquakes, color-coded by depth
Cross-section of the Tonga trench near latitude 21° S.
Colored triangles represent the location of volcanoes,
color-coded by type of volcano. Colored circles
represent earthquakes, color-coded by depth.
Continental meets more continental
Cross-section of the Himalayas along 88° E longitude.
Colored circles represent earthquakes, color-coded by depth
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Ipocenter and Epicenter
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Distance Typology
Epicentral distance
Epicenter
Site
Closet distance to the seismogenic
part of the rupture surface
Ipocentral
distance
Seismogenic
Depth
Closet distance to the rupture surface
Slant Distance
Ipocenter
Rupture
Fault
Joyner-Boore Distance
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Fault typologies
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Fault typologies
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Fault typologies
Strike-slip fault
Normal fault
Reverse fault
Normal-oblique fault
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Waves propagation
Body waves
Surface waves
Rayleigh wave
p wave
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s wave
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Love wave
Slide 13
Waves propagation
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Site response
In alluvial basins on stiff bedrock,
wave interpherences occur due to:
- multiple reflections,
- diffractions,
- body to surface mode conversions.
surface waves
reflected waves
These phenomena induce, overall:
- higher peak amplification
- significant increase of duration with respect to 1D conditions.
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Earthquake intensity
Mercalli intensity scale
The scale quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made
structures on a scale from I (not felt) to XII (total destruction). Values depend upon the distance to the earthquake,
with the highest intensities being around the epicentral area. Data gathered from people who have experienced the
quake are used to determine an intensity value for their location. The Mercalli (Intensity) scale originated with the
widely-used simple ten-degree Rossi-Forel scale, which was revised by Italian vulcanologist Giuseppe Mercalli in
1884 and 1906.
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Earthquake intensity
Mercalli intensity scale
Damage map – Irpinia Earthquake, 1980
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Earthquake intensity
Richter magnitude
His inspiration was the apparent magnitude scale used in astronomy to describe the brightness of stars and other
celestial objects. Richter arbitrarily chose a magnitude 0 event to be an earthquake that would show a maximum
combined horizontal displacement of 1 µm (0.00004 in) on a seismogram recorded using a Wood-Anderson torsion
seismograph 100 km (62 mi) from the earthquake epicenter. This choice was intended to prevent negative magnitudes
from being assigned. The smallest earthquakes that could be recorded and located at the time were of magnitude 3,
approximately. However, the Richter scale has no lower limit, and sensitive modern seismographs now routinely
record quakes with negative magnitudes.
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Earthquake intensity
Moment magnitude
Fault moment
M0 = m ∙ A ∙ D
Average offset ≈ Slip [L]
Rigidity G [F/L2]
Fault area [L2]
Moment Magnitude
M0 [dyne cm]
Kanamori 1977
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Magnitude relationship
In seismology, the Gutenberg–Richter law (GR law) expresses the relationship between
the magnitude and total number of earthquakes in any given region and time period of at
least that magnitude
or
Where N is the number of events having a magnitude > M; a and b are constants calibrated
on a given set of events.
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Magnitude relationship
The constant b is typically equal to 1.0 in seismically active regions. This means that for every
magnitude 4.0 event there will be 10 magnitude 3.0 quakes and 100 magnitude 2.0 quakes. There
is some variation with b-values in the range 0.5 to 1.5 depending on the tectonic environment of
the region. A notable exception is during earthquake swarms when the b-value can become as
high as 2.5 indicating an even larger proportion of small quakes to large ones. A b-value
significantly different from 1.0 may suggest a problem with the data set; e.g. it is incomplete or
contains errors in calculating magnitude
The a-value is of less scientific interest and
simply indicates the total seismicity rate of the
region.
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Ground Motion
prediction relations
State-of-the-art estimates of expected ground motion at a given distance from an earthquake of a
given magnitude are the second element of earthquake hazard assessments. These estimates are
usually equations, called attenuation relationships, which express ground motion as a function of
magnitude and distance (and occasionally other variables, such as type of faulting). Commonly
assessed ground motions are maximum intensity, peak ground acceleration (PGA), peak ground
velocity (PGV), and several spectral accelerations (SA). Each ground motion mapped
corresponds to a portion of the bandwidth of energy radiated from an earthquake. PGA and 0.2s
SA correspond to short-period energy that will have the greatest effect on short-period structures
(one-to two story). PGA values are directly related to the lateral forces that damage short period.
Longer-period SA (1.0s, 2.0s, etc.) depict the level of shaking that will have the greatest effect on
longer-period structures (10+ story buildings, bridges, etc.). Ground motion attenuation
relationships may be determined in two different ways: empirically, using previously recorded
ground motions, or theoretically, using seismological models to generate synthetic ground
motions which account for the source, site, and path effects. There is overlap in these approaches,
however, since empirical approaches fit the data to a functional form suggested by theory and
theoretical approaches often use empirical data to determine some parameters.
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Ground Motion
prediction relations
The ground motion at a site, for example Peak Ground Acceleration depends on the earthquake
source, the seismic wave propagation and the site response. Earthquake source signifies the
earthquake magnitude, the depth and the focal mechanism, the propagation depends mainly on
the distance to the site. The site response deals with the local geology (site classification); it is the
subject of microzonation.
The basic functional (logarithmic) form for ground motion attenuation relationship is defined as
(Reiter 1990)
ln Y = ln b1 + ln f1(M) + ln f2(R) + ln f3(M,R) + ln f4(P) + ln e
Where: Y is the strong motion parameter to be estimated (dependant variable), it is lognormal
distributed; f1(M) is a function of the independent variable M, earthquake source size generally
magnitude; f2(R) depends on the variable R, the seismogenic area source to site distance;
f3(M,R) is a possible joint function between M and R (for example for an earthquake with big
magnitude the seismogenic area is large and the source to site distance may be different);
f4(P) are functions representing possible source and site effects (for example different style of
faulting in the near field may generate different ground motions values Abrahamson and
Shedlock (1997)); e is an error term representing the uncertainty in Y
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Ground Motion
prediction relations
Sabetta e Pugliese (attenuation law for Italy)
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Seismic zoning
Punctual source: this typology of modeling it’s used for fault very deep or very
far from the interest area.
Linear source: this typology of modeling it’s used with hypothesis that all the
point of the line can be fracture point with the same probability.
Planar source: this typology of modeling it’s used with hypothesis that all the
point of the line can be fracture point with the same probability.
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PSHA
Probabilistic Seismic Hazard Analisis
For each Seismic zones target is to evaluate the annual exceedance frequency of a given
intensity trough the follow integral:
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PSHA
Probabilistic Seismic Hazard Analisis
Starting from the knowledge of Seismic Zone Typology, of Attenuation Law and G-R Law is
possible to evaluate:
Extension to more Seismic Zones
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PSHA
Probabilistic Seismic Hazard Analisis
To convert the annual rate of events to a probability, we consider the probability that the ground
motion exceeds test level x at least once during a specific time interval. A standard assumption is
that the occurrence of earthquake is a POISSONIAN process.
For t=1 this probability is the annual hazard. Starting from previous relation is possible to obtain
the Return Period of the generic event that has an exceedance probability of P in time t:
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Deaggregation of Hazard
The hazard curve gives the combined effect of all magnitudes and distances on the probability of
exceeding a given ground motion level. Since all of the sources, magnitudes, and distances are
mixed together, it is difficult to get an intuitive understanding of what is controlling the hazard
from the hazard curve by itself. A common practice is to break the hazard back down into its
contributions from different magnitude and distance pairs to provide insight into what events are
the most important for the hazard.
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Example
Site and Event description
The example site considered has two faults. Fault A, produces earthquakes with magnitude
M=6 and distance R=10km from the site; and has an annual occurrence rate of l=0.01; we
denote this earthquake Event A. Fault B produces earthquakes with magnitude M=8 and
distance R=25km from the site, and has annual occurrence of l=0.002; we denote this
earthquake Event B. Both events have strike slip mechanism.
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Example
PSHA Computation
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Example
Deaggregation of Events
In this simplified site, each event (Eventj) corresponds to a single magnitude (mj) and distance
(rj). The conditional probability that each event causes Sa>y is given by follow equation:
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Example
Deaggregation of Magnitude
The deaggregation mean magnitude associated with a specific GMPM can be found using
equation:
Bold line
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Example
Deaggregation of Distance
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