comparative studyof the intraplateBasel - ETH E

DISS. ETH NO. 15537
Adaptation of the paleoseismologicalapproach to local
tectonic regime: comparative study of the intraplate BaselReinach fault, Switzerlandand the interplate North
Anatolian fault, Turkey.
A dissertation submitted to the
SWISS FEDERAL INSTITUTEOF TECHNOLOGYZÜRICH
For the Degree of
Doctor of Sciences
Presented by
FERRY, MATTHIEU ALEXIS
DEA IPGS EOST STRASBOURG
Born March 23rd, 1973
Citizen of France
-
-
Acceptedon the recommendationof
Prof. Dr. D. Giardini, examiner
Prof. Dr. M. Meghraoui, co-examiner
Prof. Dr. A. Pfiffner, co-examiner
Prof. Dr. R. Armijo, co-examiner
2004
Abstract
The assessment of seismic risk in a given region relies on the proper estimate of
related seismic hazard, i.e. the probability that an earthquake of said magnitude
occurs
within
a
said time window.
Calculating
that
probability requires
a
precise
knowledge of local seismotectonic parameters such as the frequency of damaging
earthquakes, their magnitude and the annual deformation rate. These parameters
may only be properly determined when observed over a representative time window.
As return periods for strong earthquakes vary between a few decades and several
millennia, instrumental and historical seismological datasets often prove to be
insufficient. To improve the completeness of available seismicity catalogues, we
applied the paleoseismologicalapproach to two different regions: the Basel region
(southern Upper Rhine Graben) which was Struck by a destructive earthquake in
1356 and the Izmit region (east of the Marmara Sea), partly destroyed in August
1999 by a magnitude 7.4 tremor.
A füll integrated study involving geomorphology, geophysics and trenching in the
Basel region led to the identification of the seismogenic fault responsible for the last
strong earthquake and to deciphering its seismic history for the Holocene. Thus, we
demonstrate that the newly identified Basel-Reinach fault is the locus for a magnitude
6.4-6.7 earthquake every -2600 years, on average. Furthermore, we give strong
evidence for the probable extension of the fault through the city of Basel to the north
and the folded Jura to the south. These results have a direct impact on the level of
seismic risk to the region as it was consequently lowered by one degree on the basis
of our original work.
We applied a similar, though adapted, approach to the North Anatolian fault around
the Marmara Sea. An extensive trenching effort combined with
ground-penetrating
profiles carried out on the Ganos fault to the west and the Izmit-Sapanca
segment to the east evidence several recent events and yield measurements of
pertaining co-seismic offsets. They clearly show characteristic behavior on both sides
of the Marmara Sea, however with varying offsets: 4 to 5 m for the Ganos fault and 2
to 2.5 m for the Izmit-Sapanca segment. This brings new constrains to better
characterize faulting behavior in the region and consequent seismic risk to the city of
radar
Istanbul.
5-
Resume
risque sismique dans une region donnee passe par
l'evaluation de l'aleas, c'est-ä-dire la probabilitequ'un seisme de magnitude definie
se produise dans un intervalle de temps defini. Le calcul de cette probabilite repose
sur certains parametres sismo-tectoniques locaux tels que la frequence des
tremblements de terre destructeurs, leur magnitudeainsi que le taux de deformation
annuel. Ces parametres ne seront convenablement determines qu'en disposant
d'une fenetre d'observation repräsentative des phenomenes en jeu. Face ä des
periodes de retour variant de quelques decennies a plusieurs millenaires, les
La
prise
donnees
en
compte
du
sismologiques
instrumentales et
historiques
se
revelent souvent
completer les catalogues de sismicite disponibles, nous avons
appliques les methodes de la paleosismologie ä deux regions tres differentes: la
region de Bäle (sud du Fosse Rhenan) frappee par un seisme destructeuren 1356 et
la region d'lzmit (est de la Mer de Marmara) en grande partie detruite en Aoüt 1999
par un seisme de magnitude7.4.
Une etude integree complete de la region de Bäle a permis d'identifier la faille
responsable du dernier grand seisme puis de retracer son histoire sismique
holocene. Nous avons ainsi demontre qu'elle est le lieu d'un evenement de
magnitude 6.4-6.7 tous les 2600 ans, en moyenne. De plus, nous donnons des
indications fortes sur son prolongement au travers de la viHe de Bäle, au nord, et du
Jura Plisse, au sud. Ces resultats ont une incidence directe sur le niveau de risque
sismique regnant dans la region. En effet, celui-ci a diminue d'un degre depuis la
prise en compte de ces elements jusqu'ici inedits.
Nous avons applique une approche similaire, quoique adaptee, ä la faille Nord
insuffisantes.Afin de
Anatolienne autour de la Mer de Marmara. Une campagne de tranchees menee sur
la faille de Ganos ä l'ouest et sur le segment Izmit-Sapanca ä Test ainsi que des
profils de radar geologique ont mis en evidence plusieurs evenements recents et
permis de determiner l'amplitude des mouvementsco-sismiques produits lors de ces
seismes. Ceux-ci montrent clairement un comportement caracteristique des deux
cotes de la Mer de Marmara, avec toutefois des deplacements co-sismiques
differents : 4 ä 5 m pour Ganos et 2 ä 2.5 m pour Izmit-Sapanca.