IGCP-659 ANNUAL MEETING

Meeting's Objective


IGCP-659 ANNUAL MEETING
Seismic Hazard and Risk in Africa


5th November 2020
09:00 – 18:00

The technical and scientific IGCP-659 meeting addresses the topic on the seismic risk assessment in Africa. Presentations and discussion sessions are programmed on some targeted capital cities for the hazard and risk assessment. This year 2020, the IGCP-659 working group will meet in Sousse, Tunisia alongside the 3rd CAJG in order to establish plans for practical activities related with seismic risk reduction in selected major cities in Africa.

The meeting will focus on the following topics:

1. The regional seismotectonic, seismic zonig and hazards in Africa.
2. The perspectives for the seismic hazard assessment and risk mitigation of selected African capital cities located in seismically active zones.
3. Test sites for a warning seismic system in Africa.
4. The Challenge of a Seismological Center in Africa: Virtual or Continental-based Scientific Infrastructure.

The program of the IGCP-659 meeting includes a field trip to sites with earthquake damage in the cities of Sousse and Kairouan. The field trip is planned on 29 October 2020 and will be open to IGCP-659 working group only. The field trip is sponsored by the National Office of Mines in Tunisia.


Keynote


Tsunami risk along the Eastern African coast from mega-earthquake sources in the Indian Ocean

5th November 2020
09:30 - 10:00

  • Contact

    Emile A. Okal

    Guest of Editorial Board
    Arabian Journal of Geosciences
    Northwestern University, Evanston, USA

 


Organizing Team


This IGCP-659 meeting in Tunisia is organized by:

  • Contact

    Mustapha Meghraoui

    Associate Editor
    Arabian Journal of Geosciences
    IPG Strasbourg, France

  • Contact

    Najla Bouden-Romdhane

    Guest of Editorial Board
    Arabian Journal of Geosciences
    ENIT, Tunis, Tunisia

  • Contact

    Paulina Amponsah

    Guest of Editorial Board
    Arabian Journal of Geosciences
    Ghana Atomic Energy Commission, Ghana

  • Contact

    Nejib Bahrouni

    Guest of Editorial Board
    Arabian Journal of Geosciences
    ONM, Tunisia

  • Contact

    Vunganai Midzi

    Guest of Editorial Board
    Arabian Journal of Geosciences
    CGS Pretoria, South Africa

  • Contact

    Ahmed Ksentini

    Guest of Editorial Board
    Arabian Journal of Geosciences
    Sfax University, Tunisia


Sponsors & Partners


This IGCP-659 meeting in Tunisia is supported by:

 


Course 4

Dr. Mustapha Meghraoui

Mustapha Meghraoui

Associate Editor
Arabian Journal of Geosciences
IPG Strasbourg, France

How to mitigate the seismic risk in Africa: a multidisciplinary approach

2nd November 2020
08:00 – 12:30
14:00 – 16:00
18:00 – 19:00

 

Participation Fee:

0 Euros (student)
50 Euros (academic)
100 Euros (professional)

The technical and scientific IGCP-659 meeting alongside the 3rd Springer CAJG will address the topic of seismic risk assessment in Africa. Presentations and discussion sessions are programmed on some targeted capital cities for the hazard and risk assessment. The IGCP-659 working group will meet in Sousse in order to establish plans for practical activities related with seismic risk reduction in selected major cities in Africa. For more details, see IGCP-659 ANNUAL MEETING.


The IGCP-659 working group also organizes a training course dedicated to PhD students and young researchers in active tectonics, seismology, geology and geophysics, seismic hazard and risk assessment. The training course will cover:

  • Updated techniques for seismic source characterization from tectonic-remote sensing, seismology and geodesy (GPS).
  • The hazard and risk evaluation from multi-disciplinary approaches and most recent experiences.

Participation Fee:

0 Euros (student)
50 Euros (academic)
100 Euros (professional)

Objective:

The course provides the basics and necessary explanations on how multidisciplinary but closely related interdependent themes in solid earth geophysics address the issue of seismic hazard and risk assessment, in either interplate and/or intraplate domains.

About 20 - 25 (maximum) attendees of mainly PhD students and young researchers are expected to attend this one-day course. However, senior participants are also welcome to attend.

The course will be based on 5 modules of 1h each (45' lecture, 15' exercise) except for module 5 which will be given in 2 h. We also will leave 1h at the end for a general discussion.

The course will be in English and will be based on the following 5 modules. Attendees will need a personal computer for the data treatment and exercises.

  • 08:00 – 9:00
    Module 1: Plate Tectonics, Rheology and the behavior of the African lithosphere
    Instructor: Moctar Doucouré (Nelson Mandela University, South Africa)

This first module will cover plate tectonics as it relates to the formation of the oceanic lithosphere and its mechanical behaviour, extension of such behaviour to the continental lithosphere of Africa, and relationship to earthquakes.

The mechanical behaviour of the lithosphere will be described in terms of the flexure of an elastic plate model, using the elastic thickness as characteristic parameter. This thickness will be compared to that of the seismogenic crust from which the continental lithosphere derives its effective strength. This will lead, based on considerations of continental rheology, to an analysis of the African competent lithosphere and its variation with the age of the crust or tectonic domains. Participants to the module 1 will be given an opportunity to estimate the thickness of the competent lithosphere in various crustal domains of Africa.
  • 9:00 – 10:00
    Module 2: Seismotectonics and Earthquake Geology
    Instructor: Mustapha Meghraoui (IPG Strasbourg, France)

The realistic assessment and mitigation of geological and geophysical hazards requires the characterization of the main physical parameters and development of a database at the continental and regional scale. Therefore, the development of seismotectonic studies is a necessary step for the mitigation of earthquake disasters.

In this module 2, we address the synthesis of earthquake studies and active deformation that serve as a basis for hazard calculations and the reduction of seismic risk. All large and small infrastructure projects need a seismic hazard and risk assessment due to their important implications in the socio-economic environment.

Based on the local and regional studies, the characteristics of seismotectonic studies and earthquake geology are analyzed using the following items:

  1. The building of a homogeneous database of seismic parameters, fault kinematics with location of major earthquake ruptures and source parameters.
  2. The study of neotectonic structures with the identification of Quaternary and active faulting.
  3. Emphasize the paleoseismology database and the significance of seismic cycle.
  4. Improve the seismic faulting database in regions with low level seismicity and slow active deformation.

Finally, we focus on the integration of tectonic, seismic and geodetic data into the seismic hazard assessment.

  • 10:00 – 10:30
    Coffee break

  • 10:30 – 11:30
    Module 3: Earthquake Mechanisms and their Application in Seismotectonics
    Instructor: Silvia Pondrelli (INGV-Bologna, Italy)

During this class, I will describe:

  1. different methods of computation of focal mechanisms and seismic moment tensors
  2. different catalogs available worldwide and for the Mediterranean region
  3. use of these data for seismotectonic and seismic hazard studies

1) different method of computations of focal mechanisms and seismic moment tensors.
What ’s a focal mechanism? And a seismic moment tensors? These data are a different way to describe a seismic source. When a earthquake occurs, it is possible to understand the kind of the fault and the type of motion that produced it, analysing the recorded seismograms
Focal mechanisms can be obtained using the polarities of P-wave first motion. This old method is still used mainly for low magnitude events. At present it is more diffused to compute seismic moment tensors through the inversion of seismic signals. Some methods, as for instance CMT, apply an inversion over body and surface waves simultaneously, some others use just a portion of the waveform train. We will see several examples worldwide or on a regional scale.

2) different catalogs available worldwide and for the Mediterranean region.
Several catalogs of seismic moment tensors are available worldwide and at regional scale. Worldwide, the most used and known catalog is the Global CMT Catalog, that includes CMTs for events with a Mw greater than 5.0 ooccurred all over the world starting from 1977. A well-known regional catalo is the European Mediterranean RCMT Catalog, that includes CMTs for events of moderate to great magnitude (Mw starting from 4.5) occurred in the Mediterranean region starting from 1997. After a description of these and other useful catalogs, we’ll do a roundup of focal mechanisms catalogs including informations on very old events, i.e. for the last century. A comparison between all these different dataset allows to introduce to their use and applications.

3) use of these data for seismotectonic and seismic hazard studies
As previously said, it is possible to understand the kind of the fault and the type of motion that produced an earthquake, analysing the recorded seismograms to compute a focal mechanism. A massive use of these data for a region that is active seismotectonically, allows to describe the prevailing tectonic style, the strain and stress field acting and which faults are more prone to activate. Out of the help in a description of the seismotectonic of a region, the seismic moment tensors may be the starting point to evaluate the tectonic style of future possible earthquakes. We will see some examples already applied in the Mediterranean region and in particular in Italy, to produce the most recent seismic hazard map.

Examples and exercise:
b) How to compute seismic moment tensors components from focal plane data and vice versa (es. mt2fpl.f)
c) How to compute strain and stress dominant directions starting from seismic moment tensors (PNT axes, SH min, single data or using summation results)


  • 11:30 – 12:30
    Module 4: Geodynamics and Space Geodesy (GPS - InSAR): Implications for the seismic hazard assessment.
    Instructor: Esra Cetin (Dept. of Geological Eng., Mugla Sitki Kocman University, Mugla, Turkey)

The advanced development of the modern geodetic techniques has been proved to be more powerful to reveal the geophysical phenomena. Particularly GNSS (GPS) and InSAR are initially introduced to present their contributions in studying the seismic deformations with implications in the seismic hazard assessment.

InSAR and satellite geodesy are particularly utilized to reveal the surface deformation according to coseismic and interseismic stages of the seismic cycle. On the other hand, they have also significant contributions to investigate seismic cycle related slow crustal deformations such as postseismic transients and aseismic creep.

This 3rd module will focus on:
1) The global and continuous operations of geodetic techniques that provide us high-quality spatiotemporal measurements of pre-co- and postseismic deformation, and help us understand the spatial and temporal evolution of crustal motions. An effective way to study the temporal behavior is the generation of deformation time series.
2) Accordingly, InSAR and GPS time series will be presented as they allow us to determine the slip rates across continental faults in mm/yr resolution. The main contributions of InSAR and GPS are particularly on the determination of fault parameters, the distribution and partitioning of strain along faults, and the improvement of tectonic models.
3) The monitoring of surface displacements along active faults associated with dislocation modeling contributes to improve our understanding of the driving mechanisms behind earthquakes and the interaction between them.
Finally, attendees will test the knowledge of earthquake cycle using geodetic techniques as an important step, not only for the understanding of the short and long-term Earth deformation, but also for the seismic hazard assessment and the potential for the future earthquake generation.


  • 12:30 – 14:00
    Lunch

  • 14:00 – 16:00
    Module 5: Integration of seismic, tectonic and geodetic data into the Seismic Hazard assessment and Risk Mitigation
    Instructors: Vunganai Midzi (Council for Geoscience, Pretoria, South Africa) and Ahmed Ksentini (Sfax University, Tunisia)

In this 5th module, an introduction will be presented on the Probabilistic Seismic Hazard Assessment (PSHA) and its classical formulation. We will be starting from seismic source characterization towards recurrence models and Ground Motion estimation. Attendees will learn in details all PSHA steps that include:

  • Seismic source identification according to seismicity, tectonics, geodesy and crustal models. Discussion and exercises will be presented about integrating seismicity, paleoseismological data, geology, geodesy and tectonic settings (seismogenic depths) into the source model and the recurrence equations.
  • Ground motion prediction equation integration and relevant uncertainties
  • Logic tree approach and model calibration through branches weights.
  • Open source software initiation to compute seismic hazard according to regional data.

The Seismic Risk Assessment (SRA) will be explained and will include:

  • Exposure dataset and general building stock databases
  • Fragility curves computation according to mechanistic models
  • Vulnerability analysis through empirical laws
  • Seismic risk computation, loss curves and collapse maps.
  • Mitigation practices

This module will use open source software already installed on virtual machine and can be installed in students laptops.

  • 16:00 – 17:00
    Official opening ceremony of 3rd CAJG

  • 17:00 – 18:00
    Icebreaker of 3rd CAJG / Group photo

  • 18:00 – 19:00
    Questions and General Discussion

Field Trip

Neotectonics, archeoseismology and surface effects of historical earthquakes in Kairouan area


6th November 2020

Participation Fee:

  • 20 Euros (student)
  • 50 Euros (academic)
  • 80 Euros (professional)

Leaders:

  • Néjib Bahrouni, The National Office of Mines, Tunis, Tunisia
  • Mustapha Meghraoui, Institut de Physique du Globe Strasbourg, France
  • Klaus Hinzen, Cologne University, Germany
  • Ridha Maamri, The National Office of Mines, Tunis, Tunisia
  • Faouzi Mahfoudh, The National Institute of Heritage, Tunis, Tunisia

Kairouan city was built in AD 675 at the location of the Roman town Vicus Augusti, on the Roman “via” (road) that connects Hadrametum (now Sousse) to Amaedra (now Haïdra) passing by Aquae Regia (now Haffouz). The city is limited to the east by the small lake and swamp areas of Sebkhet Sidi El Hani and Sebkhet El Kelbia. Numerous villages can be found to the west built on alluvial fan deposits of the Wadi Zeroud and Wadi Merguellil rivers. Before the Arab conquest, this alluvial plain was the site of large fields with dense olive trees and gardens to the point that the Arab leader Okba Ibn Nafaa had to order deforestation to build Kairouan (Al-Bakri, XIth century, in. Mahfoud et al., 2004). The city became a large urban area during the Aghlabids dynasty (AD 800 – 909).

The region has a low level of seismicity with shallow instrumental earthquakes that hardly reach Mw 5.5 (in INM Catalogue). However, historical documents describe the occurrence of earthquakes with significant casualties and damage. This was the case for the Kairouan AD 859 earthquake that was responsible of numerous victims, homeless people, affected the great mosque and destroyed 13 villages in the region (Al Baghdadi, Al Tabari, Ibn Al Jawzi, Ibn Al-Athir, Ibn Adhari, Ibn Taghribirdi, Al Suyuti). This seismic event reported in historical manuscripts was however considered as dubious by other historians.

Recent field investigations conducted by the National Office of Mines in Tunisia in collaboration with the Institute of Earth Physics of Strasbourg (IPGS), and The National Institute of Heritage in Tunis “unearthed” historical documents that report the earthquake damage in Kairouan and Sousse areas during the 9th century (Bahrouni et al., 2020).

During the AD 859 earthquake the great mosque of Kairouan, the houses, fortifications and bridges suffered severe damage. The historical documents report that during the rule of the local governor Ibrahim Ahmed, important reconstructions and restorations were conducted in the city, the great Mosque in particular, bridges and battlements until Sousse city. Indeed, a poster exposed into the mosque courtyard shows the Mosque construction sketches before and after AD 859. The historians also report that the city (which reached about 100 000 inhabitants) suffered of severe water shortage due to the damage that affected the Cherichira aqueduct. Initially built at the Roman time and then retrofitted during the Aghlabids period, the aqueduct used to bring fresh water from the Oueslat Jebel (mountain) to Kairouan. Following the earthquake in AD 860, the Emir Ibrahim Ahmed decided the building of the large circular cistern called Feskiya Bab Tunis (literally the cistern of Tunis door).

This one-day field trip on 6th November 2020 will present the main features, damage and neotectonic observations associated with the AD 859 earthquake in Kairouan and Sousse. The itinerary will include the following stops:

  • 08:00 Departure from the conference hotel in Sousse
  • 10:00 Visit to the aqueduct damaged bridge at the Cherichira site
  • 11:30 Departure to Kairouan
  • 12:00 Visit of open air cistern also called Feskiya of Bab Tunis in Kairouan
  • 12:30 Visit of the Great Mosque: damage disorder and reconstruction work of the year AD 860.
  • 13:15 Lunch in the old city of Kairouan
  • 14:30 Departure to Sousse
  • 15:30 Visit of the still visible stone engraving (in Arabic Koufi writing style) that commemorates the reconstruction of the southern wall of the battlements of Sousse and related fortifications in AD 859-860.
  • 16:00 Visit of the old city Kasba
  • 17:00 Departure to the conference hotel in Sousse
  • 19:00 Dinner at the hotel