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Seismic hazard in lebanon
 

Seismic hazard in lebanon

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    Seismic hazard in lebanon Seismic hazard in lebanon Document Transcript

    • Fellow Constructor S.a.r.l 16/01/2012 Seismic Hazard of LebanonReliable historical records, observational data and field information show that Lebanon is in anactive region, where high magnitude earthquakes and tsunamis have struck and destroyedBeirut several times in the past, causing severe destruction and high death tolls.Energy release associated with rapid movement on active faults is the cause of mostearthquakes; through years eleven major faults emerged within Lebanon: AT-Aakkar Thrust,DSF-Dead Sea Fault, GhF-Ghab Fault, MLT-Mountain Lebanon Thrust (newly discovered), NT-Niha Thrust, RaF-Rachaya Fault, RF-Roum Fault, SF-Serghaya Fault, TT-Tripoli Thrust, YF-Yammouneh Fault; ZCF-Zrarie-Chabriha Fault. The most recent large earthquake along the northern DSF system occurred on 25 November 1759 with an estimated magnitude exceeding 7.0. Below, a full account of the most damaging historical earthquakes in Lebanon is given. 303 Apr 2-An earthquake shook Sidon and Tyre causing a non-damaging sea wave. Many buildings collapsed, killing thousands of people. 455 Sept-An earthquake destroyed Tripoli. 476 Sept-An earthquake destroyed the town of Gabala. 551 July 9-An earthquake along the DSF was felt. It generated a seismic sea-wave off the Lebanese coast which flooded and partly flattened many cities.847 November 24-An earthquake destroyed Darayyah and Beit Lihyah along with other places.991 Apr 5-An earthquake sunk Duma into the ground.1063 Aug- An earthquake caused the walls of Tripoli to fall down, and there was widespreaddestruction in Antioch, Laodicea ,Tyre, Acre and in many other cities in both Byzantine and Arabterritory.1202 May 20- An earthquake occurred in the Middle East around daybreak. Tyre and nearbyBaalbek were mostly affected; not to mention rock falls in Mountain Lebanon that killed 200people.1354 Oct 28 - An earthquake shook Baalbek causing many casualties. References available upon request
    • Fellow Constructor S.a.r.l 16/01/20121759 Oct 30 - An earthquake totally ruined Safad and Qunaitra. The Damage extended to Saida,where a few houses collapsed. In addition to that, a tsunami flooded Acre and the docks atTripoli.1759 Nov 25 -This was a major shock which lasted 50 sec. and almost totally destroyed allvillages in a narrow zone extending to the north-east for about 120 km along the Litani andBekaa Valley into the upper reaches of the Orontes river in southwest Syria.1837 Jan 1- An earthquake occurred at about four in the afternoon and lasted about 20seconds. It was probably a multiple event, the second shock occurring about five minutes afterthe main shock. Destruction or heavy damage was done along a relatively narrow zone whichextended from the coastal area of Saida through the inland regions of al-Touffa, Marjuyum,Bshara to Lake Tiberias, for a total length of about 120 km.Maximum damage was experienced along the RF.1956 Mar 16- An earthquake shook the southwestern Lebanon range. In all, 122 people werekilled in 33 settlements and villages. The shock triggered slides, rock-falls and damagedretaining walls of mountain roads.Outside this region damage decreased rapidly with distance concentrating on vulnerable sites.In Beirut the shock was felt, at a few places causing some minor damage and the evacuation of13 old houses. The earthquake was felt as far north as Baniyas, in Damascus, Amman, innorthern Israel and in south-east Cyprus, within a radius of 170 km.Moreover, several neighboring seismic sources may affect the seismic hazard of Lebanon andare as follows: Dead Sea fault, Ghab fault, Kara, Syria region, Cyprus region. The figures shownbelow illustrate large historical earthquakes in and around Lebanon. References available upon request
    • Fellow Constructor S.a.r.l 16/01/2012 Mw 8 7.5 Magnitude 7 6.5 6 Year (gregorian) Based on the chart above, the maximum return period of an earthquake with a magnitude higher than 7.0 , since the year 1000 A.D was 139 years Such an earthquake struck the Lebanese region in 1837, i.e. 175 years ago. This puts the country in the critical time period.Seismic hazard refers to the quantitative estimation of ground shaking and its likely effects onnature and man for public safety considerations; the results of such studies are published asseismic hazard maps showing peak ground acceleration (PGA). With hazards thus determined,their risks are assessed and included in building codes and safety measures.Based on the results of a study published by “Lebanese Science Journal, Vol. 12, No. 2, 2011”,the following conclusions can be drawn:“Lebanon is a country of moderate to high seismic hazard. The expected PGA with a 10%probability of exceedance in 50 years varies mostly between 0.20 g and 0.3 g.The presence of the newly discovered Mount Lebanon thrust does indeed have a significantimpact on the earlier established seismic hazard map of Lebanon, especially for the coastal areawhere more than 70% of the country’s population and capital investments concentrate.The proposed seismic zone parameter for the coastal area between Saida and Tripoli, as well asfor the area around the central part of the Yammouneh fault should be increased from itspresent value of 0.2 g to 0.3 g. The proposed parameter for the remaining part of the country is0.25 g.This increase in seismic hazard implies that all civil engineering facilities, including buildings andbridges, that are yet to be constructed in the coastal zone between Saida and Tripoli should bedesigned using the design and reinforcement detailing requirements (in reinforced concretestructures) of “high seismic hazard” established in international codes of practice.” References available upon request
    • Fellow Constructor S.a.r.l 16/01/2012 The frequency is recorded worldwide. References available upon request