The results of the analysis, based on the parameters of events and some features of
seismicity that have occurred in the Lezha-Ulqini seismogenic zone during period of time
2001-2012, are presented in this paper. This seismogenic zone presents a significant seismic
hazard to those living in northwestern Albania, southern Montenegro not only due to the
pending earthquake but also due to a lots of earthquakes certain to follow the mainshock. In
total, 112 earthquakes are registered during overmentioned period in this zone, and one with
ML=5.0 (Richter) occurred on 21 August 2009. Lezha-Ulqini seismogenic zone present a
threat to nearby urban areas in Albania and the Montenegro. The goal of this study is to
determine tipology of seismicity, the source parameters of the mainshocks and their
aftershocks in order to shed light on the seismotectonics of the area on the stress field and to
evaluate the seismic hazard. The region affected by the August 2009 sequence, together with
the seismogenic region of the 15 Aprile 1979 Ulqini event (M7.0), forms a roughly NW−SEtrending
active seismotectonic zone in western Albania and continues through southern
Montenegro

Adisa, Daberdini

Astrit, Shatro

Edmond, Dushi

Fatmir, Basholli

Rrapo, Ormeni

Epoka University

192nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, AlbaniaRecent Seismic Activity of the Lezha-Ulqini Seismogenic Zone and itsAssociated HazardOrmeni Rrapo1, Dushi Edmond1, Shatro Astrit1,Daberdini Adisa2, Basholli Fatmir3,1Institute of GeoSciences, Energy, Water and Environment , Polytechnic University of Tirana. Address: “DonBosko” street, Nr.60, Tirane – Albania, e-mails: rrapo55@yahoo.com.2Faculty Physicis Engineer and Math Engineer,Polytechnic University of Tirana, e-mails:adisadaberdini@hotmail.com3Vitrina University of Tirana. Adress: City Park, Kashar, fbasholli@yahoo.comABSTRACTThe results of the analysis, based on the parameters of events and some features ofseismicity that have occurred in the Lezha-Ulqini seismogenic zone during period of time2001-2012, are presented in this paper. This seismogenic  zone presents a significant seismichazard to those living in northwestern Albania, southern Montenegro  not only due to thepending earthquake but also due to a lots of earthquakes certain to follow the mainshock. Intotal, 112 earthquakes are registered during overmentioned period in this zone, and one withML=5.0 (Richter) occurred on 21 August 2009. Lezha-Ulqini  seismogenic zone present athreat to nearby urban areas in Albania and the Montenegro. The goal of this study is todetermine tipology of seismicity, the source parameters of the  mainshocks and theiraftershocks in order to shed light on the seismotectonics of the area on the stress field and toevaluate the seismic hazard. The region affected by the August 2009 sequence, together withthe seismogenic region of the 15 Aprile 1979 Ulqini event (M7.0), forms a roughly NW−SE-trending active seismotectonic zone in western Albania and continues through southernMontenegro.KEY WORDS: Seismicity, Adriatic Sea earthquake, focal mechanism, faults, aftershocksI. INTRODUCTIONThe Albanian mountain belt is a segment of the Dinarides-Hellenides orogeny that trendsNNW–SSE (Fig. 1). It was formed by Alpine orogenic processes related to the Apulia andEurasia convergence and the closure of the Mesozoic Tethyan Ocean [1],[5]. In 2009 onemoderate earthquake of 21 August hit Northwestern Albania with intensity I0=VI-VII (MSK-64) (Fig. 2). This earthquake highlight the increased seismic activity of the Lezha-Ulqinseismogenic zones in 2009. During the last century, several devastating earthquakes haveoccurred, causing casualties and substantial damage [15].The epicenter of the M=5.0, 21 August 2009 earthquake, which caused no damage, was 17 kmoffshore west Albania in the Adriatic Sea. The most recent previous strong event in this regionwas the Ulqini earthquake of 15 April 1979 (GMT 06:19:40; Ms7.1; 41.94° N 19.408° E; h=8km), which caused extensive damage along 100 km of the coastline, killed 129 people, injured1554 people in the former Yugoslavia and Albania, and left more than 80,000 homeless[13].During this earthquake were observed tsunami wave with an amplitude 0.5-1 m in theUlqin coastline. Other stronger earthquakes on record in the Lezha-Ulqini-Shkodra zoneaffecting Albania and Montenegro, such as the MS6.9 earthquake on January 13, 1563; theMS7.2 July 25, 1608 earthquake; the MS7.2 and I0=X(ten) degrees  April 6 1667 earthquake; the202nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, AlbaniaMS6.6 June 1, 1905 earthquake [15]. The body waveform modeling inversion has confirm thefocal mechanism of the mainshock of 15 April 1979  as a pure thrust mechanism and rule outthe existence of considerable strike slip component in the motion. The mainshock occurredalong a shallow (depth 7 km), low angle (14°) thrust fault, parallel to the coastline and dippingto the NE. The aftershock mechanisms also demonstrate that these earthquakes were caused bya compressional regime.II. GEOLOGIC, TECTONIC / NEOTECTONIC SETTINGS OF ALBANIA ANDTHE LEZHA-ULQINI AREAFrom a geologic standpoint, Albaniabelongs to the Dinarides, the southern branch of the Alpinefolded belt. The Dinarides are separated into two portions: the Dinarides and the Hellenides.The Dinarides transition into the Hellenides in Albania, with most of the country encompassedby them where these are called Albanides. To the west, they are bounded by the Apulia-Gargano foreland. The Albanides consist of Ordovician to Quaternary magmatic andsedimentary rocks.The Lezha-Ulqin area occurred at the border of Adria microplate and the Eurasian platform,where the folded Alpine Dinarides-Albanides-Hellenides mountain ranges are located andcontinental collision occurs [2],[3]. The seismicity is distributed in tectonic units of the Lezha-Ulqin area. The area consists of three tectonic units: the Albanian Alps, the Krasta Cukali andthe Kruja units (Fig. 1). Carbonate formations from the Albanian Alps unit comprise theeastern and the northern part of region, outcropping along a narrow belt[7].Fig.1. Tectonic features of the Lezha-Ulqini-Shkodra area.The Albanian Alps do not continue further south. The cause of the southern closure of theAlbanian Alps unit is controversial: it may be related to the strike-slip Shkoder- Peje fault(known as the Shkoder–Peje transversal fault) or have another cause. To the north, theAlbanian Alps unit continues as the High Karst unit in Montenegro. The central part of theregion has been built up by the Krasta Cukali unit, which continues to the northwest in212nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, AlbaniaMontenegro, where it is known as the Budva unit. The Krasta–Cukali unit (Budva unit) iscomposed of carbonate formations, flyshes and volcano-sedimentary formations. In the east,the Albanian Alps unit over thrusts the Krasta-Cukali unit, while to the west, the Krasta–Cukaliunit over thrusts the Kruja unit. The Kruja unit forms much of the western part of the regionand is composed mainly of carbonate formations. In Montenegro, the Kruja unit is known asthe Dalmatian unit, and within the Adriatic Sea, it over thrusts the Adria platform [1],[2],[4].Insome cases where seismic energy failed to be released through these faults, reverse faults havedeveloped, as in the Ulqin area. The buried orogenic front, which trends NW here, is expressedby thrusting of the Kruja zone over the Albanian Basin.III. DATA AND METHODThese earthquakes were recorded by permanent broadband seismological stations that are partof the Albanian Seismological Network (BCI, PUK, PHP, VLO, KBN and SRN), as well byneighboring seismic networks AUTH (FNA, IGT, NEST, THE, LKD2, MEV), MSO (PDG,BEY, BRY, BDV, HCY, NKY, PVY, ULC), INGV (MRVN, NOCI, SCTE, SGRT) andMEDNET (TIR). The aftershocks were located using data from three or more seismic stations.The formula to calculate local magnitude is ML=log10(A/1000)-3.37+3·log10(D) that is dividedwith a regression coefficient for each station. The P- & S-wave arrivals from series ofearthquake are accurately re-picked to obtain a high-quality data set. This data set provideshighly precise hypocenter location determinations. The average of the root mean square (RMS)is 0.27s for all earthquakes, where minimum is 0.06s and maximum is 0.52s. The errors in theearthquake depths (vertical, error) are smaller then 3 km. The epicenters were located using Pand S onsets, a local velocity model [12], and the Hypoinverse program [9]. A complete andhomogenous catalog of earthquakes is provided. There were 112 earthquakes with 1.5≤ML≤5.0,and two of them with M ≥ 4.5 (Fig 2). The focal mechanism solutions for the 21 August 2009main-shocks and selected aftershocks are based on the classical method of first-onset polarities,using the Focmec routine in the Seisan package [6].IV. RECENT SEISMICITOn the Lezha-Ulqini seismogenic zone, 112 earthquakes with ML>1.5 were located, of which27 of magnitude ML≥3.0 , 7 of  magnitude ML>4 and the strongest event with magnitudeM=5.0 (fig 2). Focal depth analysis reveals that this seismicity was mainly generated in theupper und middle crust [10], under the tectonic conditions described previously. Larger numberof seismic events are present during 2009-2012 years .The strongest event occurred on 21 August 2009 (M5.0) and the other occurred on  26 March2012 (M4.5). These earthquakes highlight the increased seismic activity of the Lezha-Ulqiniseismogenic zone. The moderate earthquake of on  26 March 2012 (M4.5) at 04:08 local time,21km depth, occurred in the Adriatic Sea. In this serie, about 5 aftershocks with magnitudeML=2.0-3.4 were located. The 21 August earthquake hypocentral coordinates are 41.86°N and19.13°E, with a focal depth 12.9 km. In the series were located 31 aftershocks with magnitudeML=1.5-4.1 depths ranging from 1-25 km. Figure 3 shows the “b” estimate for the eleven years2001 – 2012 (about 112 events). For the period 2003-2008 the b value is increasing for eachyear because there were not  moderate events. After 2008 with the strongest event (M5.0) in2009 the b value is lower than 0.7.222nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, AlbaniaFig 2. The map of earthquake epicenters occurred in Lezha-Ulqini zone during period 2001-2012The parameter b is believed to depend on the stress regime and tectonic character of the region.Changes in b-value are believed to be inversely related to changes in the stress level. Thesmaller b-value means that the stress was high in the Lezha-Ulqini region. The major shock 21August (Ulqini) earthquake (M5.0) was   followed by a decrease in b-value in  months beforethis earthquake. Before 2009 year  the  b coefficent has smaller values correlated withincreasing stress level.Fig 3.Temporarly distribution  'b' value for each year during this century for events with ML>1.5V. INSTRUMENTAL PARAMETERS AND FOCAL MECHANISMSSOLUTIONS OF EARTHQUAKE OF 21 AUGUST 2009232nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, AlbaniaThe 21 August earthquake hypocentral coordinates are 41.86°N and 19.13°E, with a focaldepth 12.9 km. Figure 4 illustrates the distribution of aftershocks recorded from 21 August to30 September 2009 with 2.0≤ML≤4.0 on the Dalmat coast. The epicenters of these secondaryevents are located northeast of the main-shock at 5-15km depth [11]. The aftershock activitydeveloped in the seismically active upper crust beneath Albania, which has a thickness of 20-25 km [10].Aftershocks began immediately after the mainshock and were distributed along anarrow SE-NW belt with over the Adriatic coastline, but progressed towards the mainshock.The aftershock locations indicate that many occurred on subsidiary faults and were limited tothe primary fault plane. Aftershocks that were distant from the mainshock rupture planeindicate that the stresses on cracks increased as a result of the mainshock.Fig. 4. Epicenters of mainshocks and aftershocks of the earthquake that occurred in 2009 in the Adriatic Sea.We determined the focal mechanisms of the 21 August 2009 mainshock and three ML>3.7aftershocks. The parameters of the four focal mechanisms are listed in Table 1. The 21 August2009 mainshock has a strike of 158°, a dip of 50° and a rake (slip) of 90°.VI. SEISMOTECTONIC INTERPRETATIONS OF ZONES FROM SOURCESPARAMETERS OF 21 AUGUST EARTHQUAKE SEQUENCE.Here we study the rupture processes of the four strongest events in the aftershock sequence ofthe 21 August 2009 earthquake, focusing on the slip distribution along the fault planes.Analysis of the focal mechanism solution shows that the earthquake was triggered by pure242nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albaniathrust with a NE-SW direction of compression (Fig. 5). The hanging wall of the fault has a dipof 50° and its NW-SE trend is associated with activation of the Adriatic Sea deep crustal faultzone at the border of the Adriatic Sea platform and the orogen. The focal mechanism solution ofthis shallow earthquake demonstrates ongoing NW-SE horizontal compression (thrust faulting)along the Ulqincoastline.Fig.5. Detailed seismotectonic map of Lezha-Shkodra-Ulqini and the surrounding area based on seismic andgeologic data [14], and focal mechanisms of the 21 August 2009 mainshock and its aftershocks withML>3.7.The focal mechanism of the first aftershock, which occurred four minutes after the mainshock,indicates pure thrust faulting and for the 23 and 24 August aftershocks show thrust faultingwith a strike-slip component.The focal mechanisms of the mainshock and the strongestaftershocks show that the seismic activity along the Adriatic coastline in the Lezha-Ulqin zoneis due to regional compression (Table 1, Fig. 5). These earthquakes were caused by motionalong a pure thrust fault with a NE-SW compressional stress direction. The axes ofcompressional stress are perpendicular to the coast of the Adriatic Sea. The dislocation planesactivated by the earthquakes coincide with the fault planes based on geological and geophysicaldata. Thus, the 21 August 2009 mainshock was generated by the reactivation of a NW-trendingreverse fault (N22W) in the Ulqin zone.The associated seismic hazard has a direct connection with the geology of the location. While theseismic hazard resulting from thrust fault earthquake is well recognized and discussed, little attentionhas been given to quantifying the subsequent aftershock activity and its potential impact oncommunities in the region. Results of seismicity presented in this paper are intended to enablecommunity officials and the general public to better understand the Lezha-Ulqini zone earthquakesthreat and to encourage a more comprehensive discussion of the Lezha-Ulqini thrust fault zone with aNE-SW direction of compression.Table 1. The focal mechanism parameters of the Ulqin main-shock and selected aftershocks252nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, AlbaniaVII. CONCLUSIONSThis study focuses on the recent  features of seismicity of Lezha-Ulqini most seismogenic zone inAlbania.Focal depth analysis reveals that this seismicity was mainly generated in the upper and middle crust,under the tectonic conditions described previously. Analysis of focal mechanisms shows thepredominance of thrust faulting with a normal component onLezha-Ulqin in western Albaniathat is compatible with the present-day NE-SW compression.The 21 August 2009 Adriatic Seaearthquake ruptured along a dipping plane with a strike subparallel to the coastline andpredominately thrust motion. The earthquake is consistent with hypothesis of the convergenceof the Adriatic block and the European mainland. This sequence confirms the northwestcontinuation of thrust faulting along roughly NNW-SSE-trending faults related to the coastlineof the Adriatic Sea.Thrusting   faulting in Albania are likely to be the result of differences ingravitational potential energy between the lowlands of western Albania and the mountains inthe east of the country. TheLezha-Ulqin fault zones have produced earthquakes in the past, andthey are expected to continue to be active in the future. This study of   earthquakesemphasizes many geologic and seismotectonic characteristics of the areas constituting a threatfor nearby urban areas of Albania,   and Montenegro.REFERENCE[1] Aliaj, Sh. Sulstarova E. Muço, B. Koçiu, S. (2001).Seismotectonic map of Albania,schale  1:500.000. Seismological Institute Tirane[2]   Altiner, Y. Bacic , Z. Basic,  T. Ctichia,  A. Medved,  M. Mulic,  M. Nurçe  B. (2006).Present-tectonics in and around the adria plate inferred from GPS measurements.Geological society of America Special Paper 4009.[3]    Anderson, H. & Jackson, J.A (1987). Active tectonics of the Adriatic region.Geophysical Journal of the Royal Astronomical Society91, 937–983.[4]    Copley, A. Boait, F., Hollingsworth, J. Jackson, J.A. &Mckenzie, D.(2009). Subparallelthrust and normal faulting in Albania and the roles of gravitational potential energy andrheology contrasts in mountain belts. Journal of GeophysicalResearch, 114, B05407,N DateY/m/dTimeh:m:sRMS(s)Lat Long Depth(km)ML Strike Dip Rake Type ofMechanism.1 09/08/21 13:37:56 0.05 41.86 19.13 12 5.0 158 50 902 09/08/21 13:41:24 0.09 41.94 19.22 7.6 4.0 151 40 903 09/08/23 21:44:53 0.18 41.91 19.18 12 3.9 11.1 64. 564 09/08/24 00:03:22 0.24 41.90 19.18 15 3.7 108.5 90 65262nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May 2013, Epoka University, Tirana, Albaniadoi:10.1029/2008JB00593[5]    Doglioni, C. Carminati, E. Cuffaro, M& Scrocca, D.( 2007). Subduction kinematicsand dynamic constraints. Earth ScienceReviews 83, 125–175,doi:10.1016/j.earscirev.2007.04.001.[6]    Haskov,  J & Ottemoller, L. (2008).Seisan: The erthquake analysis software.University of  Bergen, Norway[7]    Kilias, A. Tranos, M. Mountrakis, D. Shallo, M. Marto, A& Turku, I. (2001).Geometry and kinematics of deformation in the Albanian orogenic belt during theTertiary.Journal ofGeodynamics 31, 169–187.[9]    Klein, F.W. (2002).Hypocenter location program Hypoinvers, USGS.[10]   Ormeni, Rr. (2007). The general model of construction of the Albanian earth crust andits seismoactive features according to the seismological data.  PhD  thesis,  Tirana.[11]  Ormeni, Rr.Öztürk, S.Gumeni, Fand Naço, P. (2010). The Adriatic sea earthquake ofAugust 21, 2009 (ML=5.0), 3rd International Earthquake Symposium, Bangladesh,Dhaka, March.5-6 2010,[12]   Ormeni, Rr. (2011). "P- & S-Wave Velocity Model of the crust and uppermost mantleof the  Albania region" ELSEVIER, Journal of Tectonophysic, Vol 497,  January 2011,pp 114_121[13]   Papazachos, B. Savvaidis, A. Papazachos, C. Papaioannou, Ch. Kiratzi, A.Muco,B., Kociu, S., Sulstarova, E.(2001). Atlas of  isoseismal maps for shallow earthquakesin Albania and surrounding area. Publ. Dep. Geophys. 10, 57.[14]   Publik Diplomacy Division NATO. (2007). “Harmonization of seismic hazard mapsfor the  western Balkan countries”, (SfP Project Number983054).[15]    Sulstarova, E. Kociaj, S. Aliaj, Sh.(1980).  “Seismic Regionalizition of Albania”,Published, Science Academy of Albania,   Tiranë.

Recent Seismic Activity of the Lezha-Ulqini Seismogenic Zone and its Associated Hazard

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Recent Seismic Activity of the Lezha-Ulqini Seismogenic Zone and its Associated Hazard

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