NATO North Atlantic Treaty Organization SCIENCE FOR PEACE AND SECURITY PROGRAMMEPublic Diplomacy Division

MINISTRY FOR ENVIRONMENTAND SPATIAL PLANNING Environmental Agency of the Republic of SloveniaSeismology and Geology Office

MINISTRY OF DEFENCEAdministration for Civil Protection and Disaster Relief

STABILITY PACT FOR SE EUROPEDisaster Preparedness and Prevention Initiative - DPPI

REPUBLIC OF SLOVENIA

FIRST WORKSHOPFOR THE NATO SCIENCE FOR PEACE PROJECT NO. 983054

“HARMONIZATION OF SEISMIC HAZARD MAPS FOR THE WESTERN BALKAN COUNTRIES”Ig near Ljubljana, Slovenia

7 – 9 November 2007

SEISMOGENIC MODELS FOR ALBANIA:SEISMOGENIC MODELS FOR ALBANIA:OVERVIEW OF RELEVANT DATA OVERVIEW OF RELEVANT DATA

Prof. Shyqyri AliajProf. Shyqyri Aliaj, , PhD in Geology (Seismotectonics)PhD in Geology (Seismotectonics)Director of Seismological Institute, TiranaDirector of Seismological Institute, Tirana

Edmond Dushi (Seismolog)Edmond Dushi (Seismolog)Head of Seismological Network DepartmentHead of Seismological Network Department

CONTENT

Introduction

Relevant Data Used to Delineatethe Seismogenic Models for Albania.

Seismogenic Models Delineated for Albania

Conclusions

INTRODUCTIONAdopting the methodology of GSHAP, we put forward the idea of a genetic two-step probabilistic assessment of earthquake hazard. According to this concept, the first, seismotectonic step involves identification of seismogenic zones, while the second, engineering step is concerned with the calculation of the seismic effect caused by these at the surface.

The delineation of seismic source zones is a fundamental step in probabilistic earthquake hazard analysis. A master seismicity source model, or so-called seismogenic model, for Albania describes the spatial-temporal distribution of earthquakes, using evidence from earthquake catalogue, seismotectonics, active faults and geodynamic models.

The seismogenic zones are delineated with two fundamental tools: a seismicity profile and the present-day tectonic regime of the region under consideration.

The earthquake epicenters are concentrated mostly along active faults or fault zones. Active faults represent zones of weakness, crustal “lesions” which open periodically and generate earthquakes. That’s why the identification of active faults is a very important step in seismotectonic analysis, requiring a good definition of seismic sources, i.e. of active faults along which the earthquakes occur. The active faults are represented on different maps for Albania, such as neotectonic, active faults and seismotectonic ones.

RELEVANT DATA USED TO DELINEATE THE SEISMOGENIC MODEL FOR ALBANIA

Earthquake Catalogue

Neotectonic Structure

Active Faults

Earthquake CatalogueThe Earthquake Catalogue of the Albanian earthquakes for historical and instrumental periods (Sulstarova et al., 1975, 2005) constitute the fundamental data for characterization of seismicity

Albania, characterized by shallow crustal seismicity, is one of the most seismically active countrys in Europe. Most strong earthquakes occur in 3 well-defined seismic belts:

I. The Ionian-Adriatic coastal earthquake belt, at the eastern margin of the Adria microplate trending northwest-southeast.

II. The Peshkopi-Korça earthquake belt trending north-south.

III. The Elbasani-Dibra earthquake belt trending north-easterly (Sulstarova et al., 1980; Aliaj, 2003).

Figure 1. The epicenters of earthquakes in Albania withM≥ 5.0 for the 20th century

(Muço et al., 2002)

The seismicity of Albania is characterized from 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 ≤ 7.0) and very seldom from strong earthquakes (M >7.0). The size of the earthquakes is given in terms of surface-wave magnitude Ms

The revised earthquake catalogue of Albanian earthquakes (Sulstarova et al., 2005) used in this analysis contains all events with M ≥ 4.5 (552 -events) from the 58 A. D. up to 2005 covering the time span of 1947 years (58-2005), occurred in the region within coordinates 39.00- 43.00 N and 18.50- 21.50 E.

Seismicity data can be divided into three time-period categories with a different determination accuracy of earthquake parameters Ho, φ, λ, h, M (time, hypocenter and magnitude):

1. Pre-1900, pre-instrumental, historical era: data sources are historical and macroseismic only (low accuracy of earthquake parameters).

2. 1900-1964, early instrumental data.

3. 1964-2005, modern instrumental data are available (the best determined earthquake data).

Figure 4. The epicenters of earth-quakes of Albania for the period 1976-2005 (M>3.0)

Figure 3. The epicenters of earthqu-akes of Albania for the period

1900-2005 (M>5.0)

Figure 2. Epicenters of historicalearthquakes of Albania for

the period 58-1900 (M > 6.0)

The analysis of completeness of the catalogue was performed according to Gasperini et al., 2000.

Using the cumulative number versustime curves, the slope changes were detected, assuming that the most recent change occurs when the data became complete for magnitudes above the reference.

These curves show, for four magnitude intervals. It is obvious that the catalogue can be considered complete for Ms≥4.5 since 1920, for Ms≥5.0 since 1890, for Ms≥5.5 1850 and Ms≥6.0 since at least 1550 (Sulstarova et al,. 2005).

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Figure 5. Cumulative number of seismic events with magnitude greater or equal to 4.5, 5.0, 5.5 and 6.0; the arrows indicate the slope change points.

Neotectonic Structure

Four large neotectonic units have been recognized in Albania based on the sense, intensity and chronology of vertical movements (Aliaj, 1998):

I. Internal Alpine unit affected by post-Pliocene extensional tectonics.

II. External Alpine unit strongly affected by pre-

Pliocene compression .

III. Periadriatic Foredeep strongly affected by post-

Pliocene compression.

IV. Foreland in Adriatic and Ionian offshore.

Figure 6. Map of neotectonic (Pliocene-Quaternary) zonation of Albania (from Aliaj, 2000a).The four large neotectonic units are noted by numbers on the map: 1. Internal unit, 2. External unit (02 = its offshore sectors3. Periadriatic Foredeep (03= its offshore sector), 04. Foreland in offshore (04a=Apulian platform, 04b=Albanian Basin).The Albanian orogenic front is cut and displaced by, from south to north, the Othoni Island-Dhermi (α), the Gjiri i Ariut-Duk(β), the north Sazani Island (γ), and the Gjiri i Drinit-Lezha (δ) strike-slip faults.

The neotectonic geomorphology of the interior of the country has a horst-graben arrangement due to Pliocene-Quaternary normal faulting, while in the external domain it is mountainous, except for the Periadriatic Depression.

The present-day tectonic stress field has been well studied via microtectonics (Aliaj, 1988) and focal mechanism solutions of earthquakes (Sulstarova, 1986; Muço, 1994).

In external domain the average axis of compression is of NE-SW direction (average azimuth 2250), while in internal domain the average axis of extension is of NNW-SSE (average azimuth 3400) (Aliaj, 1988; Sulstarova, 1986).

The internal unit comprises terrains east of Kruja Zone, while the external unit includes terrains of Kruja, Ionian and Sazani zones.

Active FaultsThree longitudinal and two transverse active fault zones are evidenced into the Albanian orogen:

1. The Ionian-Adriatic thrust fault zone, NW up to nearly NNW trending

2. The Shkodra-Mati-Librazhdi graben fault zone, NW trending

3. The Peshkopi-Korça graben fault zone, N-S trending

4. The Shkodra-Tropoja normal fault zone, NE trending

5. The Elbasani-Dibra normal fault zone, NE trending (Aliaj, 2000c)

Figure 7. Map of active fault zones in Albania (from Aliaj, 2000b)

The Ionian-Adriatic thrust fault zone, the longest fault zone along the Adriatic and Ionian coasts, is divided into three segments by the Shkodra-Peja (Scutari-Pec) and Vlora-Tepelena transversals:

a. Northern segment, WNW trending, consisted of Kruja (Dalmatian) zone pre-Pliocene pure compression thrust faults rarely cut by strike-slip faults E-NE trending, active up to present-days. This segment more than 200 km long from Lezha town west-northwestwards to Montenegro along the Adriatic coast.

b. Central segment, N to NNW trending, consisted of Periadriatic Depression post-Pliocene oblique compression thrust faults, which were cut by strike-slip faults, E-NE trending. This segment about 130 km long continues from Lezha to Vlora towns along the Adriatic coast.

c. Southern segment, NW trending, consisted of mainly Ionian zone pre-Pliocene pure compression thrust faults, active up to nowadays. The thrust faults were cut by strike-slip faults, NE and SE trending. The southern segment more than 250 km continues from Vlorasoutheastwards and further in Greece along the Ionian coast.

The Shkodra-Mati-Librazhdi graben faults zone, NW trending, is represented by three particular normal fault-controlled grabens and half-grabens, which are:

a. The Shkodra Pliocene-Quaternary graben about 50 km long; b. The Mati Miocene graben about 35 km long, c. The Librazhdi Miocene half-graben about 30 km long.

The Peshkopi-Korça graben fault zone, N-S trending for more than 230 km, is represented by particular Pliocene-Quaternary normal fault-controlled grabensand half-grabens, which from the north to the south are:

a. The Kukesi, Skavica, Peshkopi and Ohrid grabens.b. The Korça and Erseka half-grabens.This fault zone obliquely cuts the main pre-

Pliocene structures, NW trending. Normal faults bounding Pliocene to Quaternary depressions have a strike-slip component (Aliaj, 1998).

The Shkodra-Tropoja normal fault zone, NE trending for about 60 km, is consisted of normal faults, mainly along the boundary of Mirdita ophiolite zone, as well as of Tropoja Pliocene-Quaternary fault-controlled graben.

The Elbasani-Dibra normal fault zone, NE trending for about 60 km in Albanian territory, is consisted of fragmentary normal faults cutting across the Krasta zone and dividing into two main segments the Mirdita ophiolites.

SEISMOGENIC MODELS DELINEATED FOR ALBANIAFour seismogenic models for Albania have been determined last twenty years.

Longitudinal:Ionian-Adriatic [1]Shkodra-Mati-Bilishti [2]Peshkopi-Korça [3]

Transverse: Shkodra-Peja [4]Lushnja-Elbasani-Dibra [5]Vlora-Tepelena [6]

I. First earthquake source model (Aliaj, 1988), represented by 6 seismogenic zones, three longitudinal and three transverse seismogenic zones have been distinguished, as follows :

Figure 8. Map of seismogenic zones in Albania with anticipated maximum magnitudes (Aliaj, 1988).

1. Ionian-Adriatic seismogenic zone, along witch, earthquakes whith expected Mmax = 7.0- 7.4 may take place north of the Shkodra-Peja transversal and south of this feature, earthquakes with Mmax between 6.0 - 6.9 may occur (Aliaj, 1988). The seismicity across this seismogenic zone south of Shkodra-Peja transversal decreases gradually from the folded front eastwards.

2. Shkodra-Mati-Bilishti seismogenic zone, witch is capable of generating earthquakes with anticipated Mmax values 6.0 - 6.9 along the Shkodra graben, and with Mmax= 5.0-5.4 along the Kashnjeti-Bilishti segment.

3. Peshkopi-Korça seimogenic zone, where earthquakes with Mmax=6.0-6.9 may be expected along it.

4. Shkodra-Peja seismogenic zone, the seismic potential of witch is of Mmax=5.5-5.9

5. Lushnja-Elbasani-Dibra seismogenic zone, along witch the future earthquakes with surmised Mmax=6.0-6.9 can be awaited.

6. Vlora-Tepelena seismogenic zone, the anticipated seismic potential of witch is of Mmax=6.0-6.9.

II. Second earthquake source model (Sulstarova & Aliaj, 2001 with small improvements by Aliaj, 2003) represented by 8 seismic source zones.

Figure 9. Seismic source zones in Albania (from Sulstarova and Aliaj, 2001 with small improvements from

Aliaj, 2003).

Eight seismic source zones have been distinguished, as follows:

Lezha-Ulqini (LU) zone with Mmax=7. 2,Peri-Adriatic Lowland (PL) zone with Mmax=6.6,Ionian Coast (IC) zone with Mmax=7.0,Peja-Prizreni (PP) zone with Mmax=6.6,Kukesi-Peshkopi (KP) zone with Mmax=6.0,Korça-Ohrid (KO) zone with Mmax=6.7, Shkodra-Tropoja (ST) zone with Mmax=5.5, and Elbasani-Dibra (ED) zone with Mmax=6.6.

This model has been also fitted to “zoneless” methodology for seismic hazard assessment of a certain area developed by Frankel (Frankel, 1995) uses the spatially smoothed seismicity and is based on an earthquake catalogue and some well - defined faults considered as a separate model.

The main extension to Frankel’s methodology developed by Slovenian’s researchers (Poljak et al., 2000) wich is the fault rupture-oriented elliptical smoothing based on determined directions of seismogenic faults in different tectonic regions, following the computer code “Ohaz” instructions (Zabukovec et al., 2000) was applied also for the territory of Albania, which tent to describe the seismotectonic information in a quantitative way. Models of seismotectonic files has been prepared, for Albania, based mainly on the similar example of seismotectonic division of Slovenian territory.

Every seismogenic zone is characterised by one or more predominant tectonic structures (strike slip fault- s, thrust- t, and normal fault- n), their orientation (strike in degrees) and corresponding weights (the sum must equal 1) obtained through a statistical analysis of seismogenic zones.

All faults, in this seismotectonic model of Albania, statistically are represented by their weights for each seismogenic source zone separately

A1: Lezha-Ulqini A2: Periadriatik Lowland A3: Ionian coastt- 305°, 0.88 t-340°, 0.87 t-325°, 0.64s- 60°, 0.12 s-65°, 0.13 s1- 295°, 0.24

s2- 55°, 0.12A4: Peja-Prizreni A5: Kukesi-Peshkopi A6: Ohrid-Korça-

Leskovikun- 295°, 0.5 n-345°, 0.57 n-15°, 0.54n- 5°, 0.25 n- 15°, 0.43 n-355°, 0.46 n- 65°, 0.25

A7: Shkodra-Tropoja A8: Elbasani-Dibran- 35°, 0.86 n-35°, 1.0n- 55°, 0.14

Figure 10. The Seismotectonic model used for hazard analysis according to

Ohaz computer code requirements (from Aliaj, 2002)

III. Third earthquake source model by Aliaj (2002), represented by 9 seismogenic zones

The main sources for compilation of this seismotectonic model are the Seismotectonic Map of Albania, scale 1:500.000 (Aliaj et al., 2000), while for the neighbouring areas the neotectonic maps of Macedonia (Arsovski, 1997) and Kosova(Elezaj, 2002) has been used.

All faults representing the basic seismogenic structures have been statistically analysed and presented by weights for each seismogenic zone separately (Aliaj, 2002).

A1: Lezha-Ulqinit- 305°, 0.88s- 60°, 0.12

A2: PeriadriaticLowland

t- 340°, 0.87 s- 65°, 0.13

A3: Ionian Coastst- 325°, 0.64

s1- 295°, 0.24

s2- 55°, 0.12

A4: Albanian Alpsn- 35°, 0.86n- 55°, 0.14

A5: Kosovan- 345°, 0.56 n- 65°, 0.24 n- 295°, 0.12 n- 5°, 0.08

A6: Kukes-Peshkopin- 345°, 0.57n- 15°, 0.43

A7: Elbasani-Dibra-Gjilani

n- 35°, 0.59n- 65°, 0.41

A8: Ohrid-Korçaarea

n-15°, 0.43 n- 355°, 0.36

n- 335°, 0.21

A9: Adriatic platen- 290°, 0.1

IV. Fourth earthquake source model (Aliaj et al., 2004) with a few improvements, represented by 10 seismic source zones

Figure 10. Seismic source zones in Albania (from

Aliaj et al., 2004 with a few improvements).

From the considerations of present-day tectonic regime, the subset of the Albanian catalogue, the regional seismicity was divided into 10 seismic sources (Aliaj et al., 2004 with a few improvements), which includes some redefinition of 8 zones previsiouly discussed for Albania (Sulstarova and Aliaj, 2001; Aliaj, 2003) together with an interior background zone and a source zone to model earthquakes in the Skopje region (Talaganov et al., 2003).

The Kukesi-Peshkopi and Ohrid-Korçaseismogenic zones are extended in comparison with the seismicity model of Aliaj et al., 2004.

10 newly defined seismic source zones distinguished in Albania and its surroundings are following:

1. Lezha-Ulqini (LU) zone with Mmax=7.2

2. Peri-Adriatic Lowland (PL) zone with Mmax=7.0

3. Ionian Coast (IC) zone with Mmax=7.0

4. Peja-Prizreni (PP) zone with Mmax=6.8

5. Kukesi-Peshkopi (KP) zone with Mmax=6.9

6. Ohrid-Korça seismic (KO) source zone with Mmax=6.9

7. Shkodra-Tropoja (ST) zone with Mmax=6.5

8. Elbasani-Dibra-Tetova (EDT) zone with Mmax=6.8

9. Skopje (SK) zone with Mmax=6.5

10. Eastern Albanian Background (EAB) zone with Mmax=5.5

CONCLUSIONS

1. The Project SfP 983054 “Harmonization of Seismic Hazard Maps for the Western Balkan Countries”, undertaken in the framework of the NATO Science for Peace and Security Programme, is the best way and very good possibility for an appropriate seismic hazard assessment in each of our countries.

2. Regarding the probabilistic approach for seismic hazard assessment, we think that both “zone” and “zoneless”seismogenic models should be used in order to have a better judgment of gained results.

3. We consider that it is necessary to delineate a common seismogenic model for Western Balkan Countries based on joint efforts of our researchers.

Thank you