Climate change and Urban Vulnerability in Africa Assessing vulnerability of urban systems, population and goods in relation to natural and man-made disasters

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

1

“Training on the job” Course on Hazards, Risk and (Bayesian) multi-risk assessement

Napoli, 24.10.2011 – 11.11.2011

10/04/23 Fatemeh Jalayer

10/04/23 Fatemeh Jalayer Slide 2

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.


Plate Tectonics

Subduction zones Mid-Ocean ridges


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.

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.

Plate Tectonics


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

Divergent boundaries

Transform boundaries

Cross-section of the San Andreas Fault in California near latitude 36° N. Colored circles represent earthquakes, color-coded by depth

Plate Tectonics


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.

Oceanic meets continental Oceanic meets more oceanic

Convergent boundaries

Continental meets more continental Cross-section of the Himalayas along 88° E longitude. Colored circles represent earthquakes, color-coded by depth

Plate Tectonics


Ipocenter and Epicenter


Distance Typology

FaultRupture

Ipocenter

Epicenter Site

Epicentral distance

Closet distance to the rupture surfaceSlant Distance

Seismogenic Depth

Closet distance to the seismogenic part of the rupture surface

Ipocentral distance

Joyner-Boore Distance


Fault typologies


Fault typologies


Fault typologies

Strike-slip fault Normal fault

Reverse fault Normal-oblique fault


Waves propagation

p wave s wave

Rayleigh wave

Love wave

Body waves Surface waves


Waves propagation


Site response

surface waves

reflected waves

In alluvial basins on stiff bedrock, wave interpherences occur due to:- multiple reflections, - diffractions, - body to surface mode conversions.

These phenomena induce, overall:- higher peak amplification- significant increase of duration with respect to 1D conditions.


Earthquake intensityMercalli 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.


Earthquake intensityMercalli intensity scaleDamage map – Irpinia Earthquake, 1980


Earthquake intensityRichter 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.


Earthquake intensityMoment magnitude

Fault momentFault momentM0 = ∙ A ∙ D

Rigidity G [F/L2] Average offset ≈ Slip [L]

Fault area [L2]

M0 [dyne cm]

Kanamori 1977

Moment MagnitudeMoment Magnitude


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.


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.


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.


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

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)); is an error term representing the uncertainty in Y



Sabetta e Pugliese (attenuation law for Italy)


Seismic zoning

Punctual sourcePunctual source: this typology of modeling it’s used for fault very deep or very : this typology of modeling it’s used for fault very deep or very far from the interest area. far from the interest area.

Linear sourceLinear source: this typology of modeling it’s used with hypothesis that all the : this typology of modeling it’s used with hypothesis that all the point of the line can be fracture point with the same probability. point of the line can be fracture point with the same probability.

Planar sourcePlanar source: this typology of modeling it’s used with hypothesis that all the : this typology of modeling it’s used with hypothesis that all the point of the line can be fracture point with the same probability. point of the line can be fracture point with the same probability.


PSHAProbabilistic Seismic Hazard Analisis

For each Seismic zones target is to evaluate the annual exceedance frequency of a given intensity trough the follow integral:



Starting from the knowledge of Seismic Zone Typology, of Attenuation Law and G-R Law is possible to evaluate:

Extension to more Seismic Zones



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:


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.


Example

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 =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 =0.002; we denote this earthquake Event B. Both events have strike slip mechanism.

Site and Event description


Example

PSHA Computation


Example

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:

Deaggregation of Events


Example

Deaggregation of Magnitude

The deaggregation mean magnitude associated with a specific GMPM can be found using equation:

Bold line


Example

Deaggregation of Distance

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Climate change and Urban Vulnerability in Africa Assessing vulnerability of urban systems, population and goods in relation to natural and man-made disasters