Disaster Risk Preparedness & Management: Cavinato - II

ASSESSMENT ANALYSIS OF SEISMOLOGIC RISK

AND GEOHAZARD VULNERABILITY OF FIRST LEVEL

IN MAJOR CULTURAL HERITAGE SITES OF ALBANIA

Gian Paolo Cavinato (*), Llambro Duni (**), Massimiliano Moscatelli (*), Iris Pojani (**),

Maurizio Simionato (*), Giuseppe Cosentino (*), Alessandro Pagliaroli (*)

(*) CNR- Istituto di Geologia Ambientale e Geoingegneria, Rome, Italy

(**) University of Tirana, Albania

Berat, 8th May 2012Conference on Disaster Risk Preparedness and Management in Cultural Heritage Sites

Conference on Disaster Risk Preparedness and Management in Cultural Heritage Sites. Berat, 8th May 2012

ASSESSMENT ANALYSIS OF SEISMOLOGIC RISK

AND GEOHAZARD VULNERABILITY OF FIRST LEVEL IN

MAJOR CULTURAL HERITAGE SITES OF ALBANIA

Contributions

• Historical and archaeological assessment (Iris Pojani)

• Regional seismic hazard assessment (Llambro Duni)

• Local seismic hazard assessment (CNR-IGAG work group)


Risk = Hazard x Elements at risk x Vulnerability

from Managing Disaster Risks (UNESCO 2010)

Risk preparedness in CH sites



Risk preparedness in CH sites




Seismic hazard - Foreword• Surface effects due to an earthquake propagation are related to several physical

phenomena, that can be summarized in three groups as: 1) source mechanism; 2)

propagation of seismic waves; 3) site effects.

• When seismic waves propagate from a source, their amplitudes, frequencies, and

durations are modified due to local conditions. These “modifications” are globally

defined as site effects or local seismic response.

• Modifications of the seismic input for a specific site are defined in comparison to a

seismic bedrock, where the seismic signal is assumed to be unmodified. This

seismic bedrock is generally located below the ground surface and underlies the

covering geological formations inducing site effects.

• Seismic response can be defined for several sites and a map grouping zones whit

homogeneous site effects can be produced: this is the seismic microzonation.

• Seismic microzonation in urban areas is a tool suitable for planners and decision

makers. Moreover, the seismic action calculated for significant monuments is useful

for consolidation works.


REGIONAL

SEISIMC HAZARD

IN ALBANIA

Albania is characterized from an intensive seismic microactivity (1.0<M≤3.0), from many small earthquakes (3.0<M≤5.0), from rare medium-sized earthquakes (5.0<M≤ 7), and very seldom from strong earthquakes (M>7.0). CH sites


Seismic microzonation

The seismic microzonation studies are aimed at streamlining the knowledge of local seismic hazard, returning useful information for:• guiding the choice of areas for new settlements;• planning investigations and levels of detail;• establishing guidelines and criteria of interventions in urban areas and

CH sites.• defining priorities for interventions.In retrofitting of existing infrastructures or monuments, seismic

microzonation studies highlight the importance of phenomena such as possible amplification of shaking and permanent deformation.

Following the Italian "Addresses and Criteria for Seismic Microzonation" (ICMS, 2008), the levels of analysis for studies of seismic microzonation increase in complexity and effort going from level 1 to level 3:

• level 1 is an introductory level designed to divide the territory into seismic microzones qualitatively “homogeneous” in seismic perspective;

• levels 2 and 3 produces a quantitative map of seismic microzonation, by means of numerical simulations.

LOCAL

SEISIMC HAZARD

EVALUATION

When seismic waves propagate from a source, their amplitudes, frequencies, and durations are modified due to local conditions. These “modifications” are globally defined as site effects or local seismic response.


Seismic microzonation of level 1

How is created?The input information can be summarized as follow:1) topographic (e.g., maps and Digital Terrain Models) and

geomorphological (e.g., escarpments and landslides) information ;2) geological maps with information on litho-type, i.e., “different kinds of

rocks or terrains”;3) already available geological, geotechnical, and geophysical

information from boreholes and other in situ tests;4) thickness of soft geological formations covering the seismic bedrock;5) evaluation of the seismic bedrock depth from noise measurements.

What is on the map?

• Stable zones, where significant local effects of any nature are unlikely. • Stable zones susceptible to local amplifications, where intensifications

of ground motion are likely.• Zones susceptible to geological instability, in which the predominant

and expected seismic effects are due to permanent deformations.

LOCAL

SEISIMC HAZARD

EVALUATION

When seismic waves propagate from a source, their amplitudes, frequencies, and durations are modified due to local conditions. These “modifications” are globally defined as site effects or local seismic response.


GEOLOGICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION

Different lithotypes behave in different ways when interested by a seismic wave: they have to be carefully mapped.Zones susceptible of permanent deformations in seismic conditions (i.e., landslide prone areas) have also to be mapped. Apollonia


NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION

Microtremor measurementsperformed to define site the fundamental frequencies, i.e., soil resonance frequencies when affected by an earthquake event.

ApolloniaTHE MONASTERY

f0=Vs/4H


ApolloniaTHE MONASTERY

NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION

MASW enable to characterize the velocity structure of the subsoil. The lower the shear velocity Vs, the poorer the «quality» of the soil in terms of site response. The higher the velocity contrast between superimposed layers of soils, the higher the susceptibility to local seismic amplification.

700 m/s


ApolloniaTHE THEATRE

SUSCEPTIBILITY

TO INSTABILITY

Define zones susceptible to geological instability, i.e., slope instability, differential settlement, liquefaction, in which the predominant and expected seismic effects are due to permanent deformations (amplification of ground motion is also possible).

earth flowaccumulation

crowns


SEISMIC

MICROZONATION

OF LEVEL 1 OF

APOLLONIA


What is critical?

The seismic microzonation level 1 enables to divide the territory of Apollonia in two main zones: 1) the hilly area, less susceptible to seismic amplification; 2) the coastal plain, more susceptible to seismic amplification, given the presence of Quaternary very soft sediments.

Where the weaknesses are?

The main uncertainties are related 1) to not well known distribution of lithotypes characterizing the geological bedrock, and 2) to not well known thickness of the Quaternary cover in the lateral valleys and coastal plain. For this motive is desirable that these uncertainties can be reduced through i) a detailed geological-geotechnical survey of the archaeological area, and ii) the use of geophysical methods which provide information on the thicknesses of the recent soft covers.

SEISMIC

MICROZONATION

OF LEVEL 1 OF

APOLLONIA


GEOLOGICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION

Different lithotypes behave in different ways when interested by a seismic wave: they have to be carefully mapped.Zones susceptible of permanent deformations in seismic conditions (i.e., landslide prone areas) have also to be mapped.

Berat


BeratTHE CASTLE

NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


f0=Vs/4H


BeratTHE OSUM RIVER

NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


f0=Vs/4H


NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


BeratTHE CASTLE

1200 m/s


NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


BeratTHE OSUM RIVER

1300 m/s

< 200 m/s


SUSCEPTIBILITY

TO INSTABILITY

Define zones susceptible to geological instability, i.e., slope instability, differential settlement, liquefaction, in which the predominant and expected seismic effects are due to permanent deformations (amplification of ground motion is also possible).

BeratTHE HISTORIC CENTER


SEISMIC

MICROZONATION

OF LEVEL 1 OF

BERAT


What is critical?

No relevant Vs contrasts were recorded in Berat, except for the Osum River valley, even if steep slopes can induce local seismic amplification and trigger gravitational instabilities.By the way, the main geohazard affecting the city of Berat is represented by the instability of rock escarpments overlooking the historic city center. The risk related to this criticality is high in static conditions and could be even higher if a seismic event should occur.


We suggest to carry out a detailed study of structural and geomechanical setting of the limestone cropping out along the escarpments, if not already available.

SEISMIC

MICROZONATION

OF LEVEL 1 OF

BERAT


GEOLOGICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


Butrint

fault scarp


ButrintTRICONCH PALACE

NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


f0=Vs/4H


ButrintACROPOLIS

NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


topographic effect


SUSCEPTIBILITY

TO INSTABILITY

ButrintTHEATRE AND DWELLING WITH ATRIUM

differential settlements

coastal plain

faul

t sca

rp

rock falls


SEISMIC

MICROZONATION

OF LEVEL 1 OF

BUTRINT


What is critical?

The territory of Butrint is heterogeneous in terms of susceptibility to seismic amplification, due to extreme geological variability. The most critical zone in terms of possible site amplifications is the coastal plain. High susceptibility to geological instability, both for differential settlements and rock falls, is related to the presence of the fault scarp bounding the Acropolis.


The seismic microzonation of level 1 of Butrint is affected by high level of uncertainty because of the lack of information about lithology, thickness, and shear wave velocity of the lithotypes. Lithostratigraphic and geometric uncertainty could be pulled down by means of one deep borehole located close to the Vivari channel, associated with Electrical Resistivity Tomographies (ERTs) oriented perpendicular to the fault scarp. Shear wave velocity could be detected by means of MASW measurements.

SEISMIC

MICROZONATION

OF LEVEL 1 OF

BUTRINT


GEOLOGICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION


Gjirokastra


GjirokastraTHE CASTLE

NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION

Microtremor measurementsperformed to define site the fundamental frequencies.These frequencies are related to the thickness of soft soils covering the basal rigid bedrock through the shear velocity, Vs.

f0=Vs/4H

topographic effect


GjirokastraTHE STADIUM

NEW

GEOPHYSICAL

SURVEY FOR

LEVEL 1 SEISMIC

MICROZONATION

Microtremor measurementsperformed to define site the fundamental frequencies.These frequencies are related to the thickness of soft soils covering the basal rigid bedrock through the shear velocity, Vs.


SUSCEPTIBILITY

TO INSTABILITY

GjirokastraTOPPLED BLOCKSAND ALLUVIAL FAN

historic wallsfracturedconglomerates

rafting blocks

rafting blocks

debries flows fromalluvial fan

castle


SEISMIC

MICROZONATION

OF LEVEL 1 OF

GJIROKASTRA

Z1 Z2 Z3 Z4 Z5-Z6


What is critical?

The most critical zones in terms of possible site amplifications: 1) buried narrow valleys located at the mouth of mountain streams (zone 4), carrying high volumes of coarse clastic materials to the valley Drino River; 2) narrow ridges bonding the buried valleys, where topographic effects highlighted by microtremors measurements could induce site amplification.A rigid fractured layer of conglomerates generally occupies the top of the narrow ridges (e.g., where the castle is located) and is highly susceptible to rock falls and toppling of isolated blocks.


Neither direct observation of subsoil nor Vs information are generally available for the site. No geotechnical parameters are available for a proper evaluation of the dynamic behavior of soils and rocks. An additional investigation survey and the passage to a level 3 of seismic microzonation is suggested.

SEISMIC

MICROZONATION

OF LEVEL 1 OF

GJIROKASTRA


What is useful for?

The seismic microzonation of level 3 is an advanced map that allows quantitatively to define homogeneous zones - in terms of site response - for a specific seismic input, i.e., for a specific earthquake scenario.

How is created?

The input information can be summarized as follow:

1) topographic (e.g., maps and Digital Terrain Models) and geomorphological (e.g., escarpments and landslides) information;

2) geological maps with information on lithotype, i.e., “different kinds of rocks or terrains”;

3) already available and new geological, geotechnical, and geophysical information from boreholes and other in situ and laboratory tests;

4) evaluation of the seismic bedrock depth from noise measurements.

5) seismic input from one or more earthquake scenarios.

Numerical modeling allows quantitatively to define site effects.

SEISMIC

MICROZONATION

OF LEVEL 3


Seismic microzonation of level 3 - Dynamic parameters

Vertical velocity gradient of the anthropic layer


Seismic microzonation of level 3 - Seismic input

Characteristics of the seismicity affecting Berat (left) andreference spectra selected for the microzonation (right)


Seismic microzonation of level 3 - Modeling of local

seismic response

Cross-section 2

Cross-section 7

Coliseum


Seismic microzonation maps of level 3 and response spectra

0 0 .5 1 1 .5 2P erio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pett

rale

, Sa(

g)

3 Ein p u t

0 0 .5 1 1 .5 2P erio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pett

rale

, Sa(

g)

3 Fin p u t

0 0 .5 1 1 .5 2P erio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pett

rale

, Sa(

g)

3 Gin p u t

0 0 .5 1 1 .5 2P erio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pett

rale

, Sa(

g)

3 Hin p u t

0 0 .5 1 1 .5 2P erio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pettr

ale,

Sa(

g)2 Ain p u t

0 0 .5 1 1 .5 2P erio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pettr

ale,

Sa(

g)

2 Bin p u t

0 0 .5 1 1 .5 2P erio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pett

rale

, Sa(

g)

2 Cin p u t

0 0 .5 1 1 .5 2P e rio d o , T (s)

0

0 .2

0 .4

0 .6

0 .8

Acc

eler

azio

ne s

pettr

ale,

Sa(

g)

2 Din p u t

ARCH OF TITUS

SAN TEODORO’SCHURCH

ARCH OF TITUS

SAN TEODORO’SCHURCH

lower orno mplification

higheramplification


Concluding remarks and future works

• Cooperation among the involved Institutions has been crucial for the project.

• The application presented in this work clearly demonstrates the potential for

full integration of geological, geophysical, and archaeological methodologies.

• Seismic microzonation in historical centers and archaeological areas is

strongly conditioned by the availability of data. For the sites of this project,

scarcity of data is the main factor affecting the reliability of seismic

microzonations of level 1.

• An integration of existing surveying is recommended for all the investigated

Albanian Cultural Heritage sites. Seismic microzonation of level 3 is

recommended for evaluating local seismic amplification, aimed at seismic risk

prevention and mitigation.

• Regarding seismic microzonation, addenda to available guidelines (i.e., for

seismic microzonation) is specifically required for archaeological areas or for

historical center of ancient and permanent urbanization.


Coming soon

Special issue of the Bulletin of Earthquake Engineering on:

Seismic Microzonation of the Central Archaeological

Area of Rome Editors: Massimiliano Moscatelli, Alessandro Pagliaroli, Gian Paolo Cavinato

(National Research Council), Sergio Castenetto, Giuseppe Naso (Italian Civil

Protection Department)

Contribution focused on:

Cultural heritage - proposal of guidelines for

evaluating local seismic hazard

Education

Disaster Risk Preparedness & Management: Cavinato - II