Effect of Directivity in Northeastern ALBANIA (5.4 MW) Earthquake of September 6, 2009, from Radiated Seismic Energy

We have quantitatively estimated an observed directivity effect, direct from the radiated seismic energy of September 6, 2009, in north-eastern Albania. Despite its moderate magnitude (Mw = 5.4), much damage was caused from this earthquake in its epicenter area, being broadly felt. Field observations, in near field to the causative fault, demonstrated a directional shaking effect pronounced mostly westward with severe effects at Çereneci and Shupenza localities. Earthquake has been instrumentally recorded from ASN and several regional broadband seismic stations, being thus the strongest event occurred since 2007, within Albanian territory. We estimated the radiated seismic energy from corrected broadband waveforms. It is considered as the most important parameter relating the dynamics and the observed directivity effect of the causative fault. A finite source model is considered, though in its simplified form it was assumed as a point source, an approximation used throughout the spectral analysis. Based on energy we could estimate the effect of directivity varying within the interval 0.0004 - 6.0, as an absolute factor on cumulative spectrum at different azimuthal angles on the focal sphere. Results are in accordance with fault geometry determined from focal mechanism solution. Earthquake of September 6, 2009 was caused from a normal fault system, striking 2200, dipping 400 and slipping -900. The effect of directivity on radiated energy, in far field was more pronounced at TIR and PUK stations and less detected at PHP and BCI stations, nearly at the opposite of the active fault striking direction

ANOMALOUS OF LOW-VELOCITY ZONE, THERMAL WATER AND SEISMICITY IN THE ELBASAN-DIBRA FAULT ZONE

A detailed investigation of the hypocenter distribution beneath Elbasani, Albania, reveals a NE-SW-trending linear alignment of seismicity within the Elbasani-Dibra transversal zone. In the zone of Elbasani, hot mineral water (thermal waters) spot out from natural springs which have been known since the 19th century. We estimate the 3D seismic velocity structure in the Elbasani zone to understand the factors controlling the genesis of such earthquakes. A narrow low-velocity zone is imaged within the transversal fault zone over a length of ∼50 km, which partly penetrates into the mantle. The low-velocity zone correlates in space with the NE-SW trending earthquake cluster. A reactivation of thermal water fracture zone is probably related to the low-velocity anomaly.Where geological conditions are favourable, rainwater seeps through the surface and becames trapped in vast underground reservoirs so deep below the Earth”s surface that it becomes heated to high temperatures by the LVFZ. The typology of earthquakes in Elbasan-Dibra comprises all three main well-known types of earthquakes: the earthquakes with main-shock followed by aftershocks, the earthquakes with foreshocks, the compound earthquakes, and the swarms. Seismic hazard for series of earthquakes in this urban area is very high and direct connection with the geology and hydrogeology of the location

Regional and temporal evaluation of seismicity in the Vlora-Elbasani-Dibra Transversal Fault Zone, Albania

Characteristics of seismic activity along the Vlora- Lushnja-Elbasani-Dibra (V-L-E-D) Transversal Fault Zone are analyzed between 1964 and 2015. There are a total of 2814 events in the time interval 1964 and 2015 with Md1.7. This study is focused on the correlation of seismotectonic b-value, precursory quiescence Z-value, and interrelationships between some other seismicity parameters. The distribution of the relatively low b-value coincides with the tectonic compression field which acts along the V-L-E-D Transversal Fault Zone. The distribution of the relatively low b-value coincides with the tectonic compression field which acts along the V-L-E-D Transversal Fault Zone. Anomalously low b-value areas coincide more or less with the spatial distribution of M≥5.0 earthquakes and their known rupture extents. Temporal changes in b-value may be related to the stress variations in these times before and after the main events. The lowest Z-values show that the variations in seismic activity rate are not significant, and the highest Z-values demonstrate a decrease in seismicity rate. In the Z-value maps for all parts of the V-L-E-D, three areas exhibit significant seismic quiescence: centered at 41.00°N-19.78°E (region A, around Lushnja), 40.99°N-20.03°E (region B, in the Cerriku), 40.81°N-19.86°E (region C, including Kucova). In addition to these three significant areas, there are some small quiescence areas in different parts of the V-L-E-D

An Application Of The Aftershock Probability Evaluation Methods For Recent Albania Earthquakes Based On Gutenberg-Richter And Modified Omori Models

In this study, an assessment on the aftershock occurrence probability based on the combination of Gutenberg-Richter and modified Omori formulae is made in order to forecast how many large aftershocks should follow small main shocks and in order to evaluate aftershock probability that a randomly chosen event is greater than or equal to a certain magnitude of aftershock. For this purpose, we made an application of aftershock probability evaluation methods to nine aftershock sequences in which occurred Albania between 2004 and 2009 with magnitude level between 4.5 and 5.0

Assessment Of The Seismoactive Layers And Features Of The Albanian Earth's Crust.

Accurate assessment of seismoactive layers represents large interests for recognition of real depth of seismic energy generation.The database of this study are relocated earthquakes of period 2001-2010 that are in considerable numbers, and due to the digital equipment records errors in determining of the depths are less than 3 km. Depth of generating earthquakes represent interest for seismoactive studies especially in seismic hazard assessment. Shallow earthquake with low energy causes higher damage in buildings than a deep earthquake with higher energy. In this study we present the determination of fault zones and low speed zones, which enable us for correct interpretations of Geodynamic phenomena of the Earth's crust. We can say that, these layers are promoters of seismic activity in Albania and can explain mobility of the earth's crust blocks and generating earthquakes from this movement. Most seismic events across our country have occurred in middle and upper crust of the earth. Based on the depths of earthquakes data is showed that the seismoactive layer in Albania earth crust has the bottom in the depth of about 20-25 km. These results are first steps towards more detailed geodynamic and seismotectonic analysis. In conclusion the hypocenter of earthquakes in the territory of Albania and its surrounding earth crust are explaned with active fault zones and lower velocity zones

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

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

Reflections from the 2019 Durrës Earthquakes: An Earthquake Engineering Evaluation for Masonry Typologies

Two earthquakes struck the NW region of Albanian territory on 21 September 2019 (Mw = 5.6) and on 26 November 2019 (Mw = 6.4). The epicenters of the seismic activity were located offshore NW Durrës, one of Albania’s most populated cities, located 30 km from the capital Tirana. Various aftershocks followed subsequently. While there were no reported injuries, a number of buildings sustained significant damage near the epicenter following the initial event. Subsequently, during the second event, there was loss of life and extensive damage to civilian structures, resulting in multiple collapses. This study focuses on the earthquake damages observed in residential and public buildings in the earthquake-affected region. The earthquakes predominantly affected low-rise masonry buildings, while the newly constructed RC structures built according to the latest seismic rules were almost unaffected. The commonly encountered building typologies in the region, together with photos showing the amount of destruction are presented here. As observed by the authors during the reconnaissance visit to the stricken area, examples of various damage patterns are presented, along with a technically substantiated description of the reasons for those damages. Although modern buildings during recent earthquakes in the region show acceptable performance, the detailed surveys from the Durrës Earthquakes showed that there is still an important level of deficiency in current masonry buildings built by conventional methods and materials. This problem may reoccur in future earthquakes that may hit other rural regions of Albania, which must be focused on systematically in the near future