A modelling study on tsunami propagation in the Red Sea: Historical events, potential hazards and spectral analysis

A modelling s udy on sunami p opaga ion in he Red Sea: His o ical e en s, po en ial haza ds and spec al analysis J.M. Ab il, R. Pe iáñez ⁎ Dp o. Física Aplicada I, ETSIA, Uni e sidad de Se illa, C a. U e a km 1, 41013-Se illa, Spain Keywo ds: Red Sea Tsunami Nume ical simula ion Fluid dynamics Spec al analysis ABSTRACT This wo k epo s esul s om nume ical simula ions o he sunami igge ed by 1995 Nuweiba ea hquake, in he Gul o Aqaba, which a e consis en wi h he a ailable obse a ions. A se ies o 12 po en ial sunamigenic sou ces a e hen conside ed in he Red Sea: ela ed o majo subma ine ea hquakes; olcanism (en y o py oclas ic flows and calde a collapse) and subma ine landslides. Nume ical simula ions ha e been ca ied ou o sol e he spa ial dis ibu ion o maximum ampli udes o wa e ele a ions and cu en s, and he flooded coas al a eas. The peak ene gy in he simula ed e en s ange om 1 k (1 k =4.18×10 12 J) up o 1.5 M , and global flood olumes ange om 0.005 km3 up o 4.4 km3. A linea co ela ion can be es ablished be ween bo h magni udes o he se o sunamis igge ed by ea hquakes up o 300 k . Tsunamis igge ed by subma ine landslides show high di ec ionali y, bu hey occu in deep wa e s and showed lowe impac s on he sho eline, as hose igge ed by olcanism. A FFT analysis shows ha in his basin, sunamis exci e low equency cons i uen s which can be in e p e ed as eigenmodes. High equencies a e exci ed only in he p oximi y o he sou ce, and he Gul o Suez exci es only hose eigenmodes close o he ones o he main basin. 1. In oduc ion The geodynamics o he Red Sea a ea is go e ned by he in e ac- ions be ween he A ican, A abian and Le an ine-Sinai pla es, being he mos ele an geophysical ea u es he Ri o Suez, he Dead Sea shea zone, he Red Sea Ri and he A a iple junc ion (Mascle e al., 2000; Boswo h e al., 2005; d'Almeida, 2010). This complex ec onic is esponsible o in ense ea hquake and olcanism ac i i y. Seismici y in he a ea has been s udied, among o he s, by Fos e and Jackson (1998),Boswo h e al. (2005) and Mohamed e al. (2012). La ge ea hquakes a e possible pa icula ly along he Gul o Aqaba-Dead Sea ans o m and he No he n Red Sea iple junc ion poin (Mohamed e al., 2012). The majo ecen e en s we e he 1995 Nuweiba ea h- quake in he Gul o Aqaba, wi h magni ude M w =7.3 (on June 2015 ano he e en in he same a ea eached magni ude 5.5); and he 1977 Massawa ea hquake in sou he n Red Sea, wi h M w =6.6. The Abu Dabbab seismogenic zone ex ends offsho e in he Red Sea and i is cha ac e ized by “cannon”ea hquakes, long con inued seismic ac i - i y, and equen ea hquake swa ms. An unique p ope y is ha ea hquake signals can be hea d by humans due o he loca ion o an ac i e aul below a la ge, igid, non-de o med block o P ecamb ian igneous ock, which eaches a dep h o ∼10 km (El Kh epy e al., 2015). The Zubai a chipelago, along wi h he Jebel a Tai and he Hanish-Zuku islands a e he main exponen s o olcanism in he sou he n Red Sea. F om Sep embe 2007 o Janua y 2008 he Jebel a Tai e up ion e en ook place, which expelled a bulk olume o 2.2×10 7 m 3 o la a (Xu and Jónsson, 2014). In 2011–2013 subma ine e up ions lead o he o ma ion o wo new olcanic islands in he Zubai a chipelago (Xu e al., 2014). A he cen al Red Sea, Miocene e apo i es, kilome e s in hickness, we e deposi ed du ing i s con inen al i ing phase, la e being co e ed wi h hemipelagic sedimen s o up o some hund ed me e s hick. Mi chell e al. (2010) iden ified a ema kable se ies o s uc u es esembling iscous g a i y flows a ound The is Deep, and in e p e ed as flowage o he e apo i es. They ound flow-pa allel lineamen s and ex ensional aul s lying, espec i ely, pa allel and o hogonal o he di ec ion o maximum seabed g adien . Feldens and Mi chell (2015) ha e iden ified six sal flows wi h heigh s o se e al hund ed me e s and wid hs be ween 3 and 10 km a ound The is Deep and A lan is II Deep, and be ween A lan is II Deep and Po Sudan Deep. They ound flow speeds o se e al mm/yea o he offsho e sal flows in ce ain loca ions. Mass was ing e en s ha e no been iden ified, al hough in o he scena ios sal ec onics ha e igge ed some gian g a i y-d i en landslides (Loncke e al., 2009). The in ense ea hquake and olcanism ac i i y may ha e igge ed la ge sunamis in he pas . Thus, Shaked e al. (2004) p o ided ⁎ Co esponding au ho . E-mail add ess: [email p o ec ed] (R. Pe iáñez). MARK Canal, o g ea comme cial and s a egic alue (Finkl e al., 2012). The model is b iefly desc ibed in Sec ion 2.1 and he diffe en sunami sou ces a e p esen ed in Sec ion 2.2. Resul s a e desc ibed in Sec ion 3. Ini ially, he simula ion ca ied ou o he 1995 Nuweiba Ea hquake, o which some obse a ional da a exis , is p esen ed (Sec ion 3.1). Then, esul s on he po en ial sunamis igge ed by o he ea hquakes, landslides and olcanic ac i i y a e desc ibed (Sec ion 3.2). The spec al analysis which has been ca ied ou is desc ibed in Sec ion 3.3.Some gene al discussion on sunami haza d in he Red Sea closes he pape (Sec ion 3.4). 2. Me hods 2.1. Model desc ip ion The sunami p opaga ion model is based on he 2D dep h-a e aged ba o opic shallow wa e equa ions, which desc ibe he p opaga ion o su ace shallow wa e g a i y wa es. The nume ical ool has been adap ed om p e ious wo ks, and i has p o ed o be a e y obus compu a ional ool (Pe iáñez and Ab il, 2013, 2014a, 2014b). The wo componen s o he dep h-a e aged wa e cu en (u, ,in he eas -wes and sou h-no h di ec ions, espec i ely), along wi h he wa e su ace ele a ion abo e he e e ence le el, ζ, a e gi en by he equa ions o conse a ion o mass and momen um: ζ x Du yD ∂ ∂+∂ ∂()+ ∂ ∂()=0 (1) ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ u uu x u ygζ xΩ τ ρD Au x u y ∂ ∂+∂ ∂+∂ ∂+∂ ∂−+ = ∂ ∂+∂ ∂ u2 2 2 2(2) ⎛ ⎝ ⎜⎞ ⎠ ⎟ u x ygζ yΩu τ ρD A x y ∂ ∂+∂ ∂+∂ ∂+∂ ∂++ = ∂ ∂+∂ ∂, 2 2 2 2 (3) whe e his he undis u bed wa e dep h, ζis he displacemen o he wa e su ace abo e he undis u bed sea le el measu ed upwa ds, D hζ=+ is he o al wa e dep h, Ωis he Co iolis pa ame e (Ωwλ=2 sin , whe e wis he Ea h o a ional angula eloci y and λ is la i ude) and Ais he ho izon al eddy iscosi y. τ u and τ a e ic ion s esses which ha e been w i en in e ms o a quad a ic law: τ kρu u τ kρ u =+=+ u 22 22 (4) whe e k is he bed ic ion coefficien . All he equa ions a e nume i- cally sol ed using explici fini e diffe ence schemes (Kowalik and Mu y, 1993) wi h second o de accu acy. In pa icula , he MSOU (Mono onic Second O de Ups eam) is used o he ad ec i e non- linea e ms in he momen um equa ions. Values o k =0.0025 and A=10 m 2 /s ha e widely p o ed hei use in models o ide and sunami p opaga ion (e.g., Pe iáñez and Ab il, 2013, 2014a, 2014b). The model domain (Fig. 1) ex ends om 32.0°E o 45.0°E, and om 10.0°N o 30.5°N, wi h a spa ial esolu ion o 60 s o a c. A highe esolu ion sub-domain has been used o he no he n Red Sea, which is 30 s o a c esolu ion, and ex ends om 32.0°E o 39.0°E and om 24.0°N o 30.0°N. The ba hyme ies ha e been ob ained om he GEODAS and GEBCO08 (60 and 30 s o a c espec i ely) da abases, a ailable on-line. Due o he wide ange in la i ude, he Co iolis pa ame e and he spa ial esolu ion in longi ude a e allowed o a y wi h λ. The con inui y equa ion was app op ia ely w i en o accoun o such a ia ion in x Δ . Time s eps o 1 s and 2 s we e fixed o he 30″ and 60″ mesh esolu ions, espec i ely. A g a i y wa e adia ion condi ion is used o sea su ace ele a ion (Pe iáñez and Ab il, 2014a) along he open bounda y in he sou h- eas e n side o he domain. A we ing/d ying algo i hm is implemen ed ollowing he nume ical scheme desc ibed in Kamp (2009). I allows he calcula ion o unup o e land. S ill wa e s (ze o wa e ele a ions and eloci ies o e all he domain) a e used as ini ial condi ions in all e idence o a ca as ophic sedimen a y e en a he no h-wes ma gins o he Gul o Aqaba, da ed a 2.3 ka BP, ha killed he Ela inging co al ee . The e en would ha e been likely igge ed by a sunami. Salem (2009) epo ed e idences o paleo- sunami deposi s on a coas al a ea o he Red Sea no h o Ma sa Alam ci y, Egyp . The Red Sea coas line is mos ly a dese and, his o ically, only e y ew pe manen human se lemen s ha e been loca ed he e. Fo such dese egions i is difficul o es ablish an accu a e ca alogue o his o ical sunamis. The NGDC/WDS Global His o ical Tsunami Da abase (NGD, 2016) eco ds 5 sunamis in he las millennium. In 1068 a sunami o igina ed in he Gul o Aqaba a 34.950°E, 29.500°N, wi h in ensi y 4.0 in he NEAMTIC scale. In 1879 a sunami was igge ed by a ea hquake wi h epicen e in he Gul o Suez (33.000°E, 29.000°N). A To , in Sinai, a sea-wa e flooded he illage. A landslide is a possible sou ce o his sunami, bu he e is no any documen a- ion in he his o ical eco ds (Jo dan, 2008). A damaging ea hquake occu ed in E i ea in July 1884, wi h epicen e offsho e Massawa (39.600°E, 15.700°N). High sea wa es buil up in he ha bo o his ci y and he sea flooded he land se e al imes. On Ma ch 1969 an ea hquake wi h epicen e in he Gul o Suez (34.000°E, 27.700°N) affec ed he islands o Shadwan, Tawila and Gubal. Dead fish and some agi a ion o he sea we e no iced a e he main shock. A s ong ea hquake, M w =7.3, occu ed in he Gul o Aqaba on 22 No embe 1995, wi h epicen e a 34.75°E, 28.97°N (Bae e al., 2008). In he ci ies o Aqaba (Jo dan) and Eila (Is ael), a he no he n eaches o he gul , a small wa e swep he beach acco ding o wi nesses (Klinge e al., 1999). Majo damage occu ed a he ci y o Nuweiba, whe e fi e people died and 11 we e inju ed. Many buildings and he ha bo a ea suffe ed s uc u al damage, and lique ac ion phenomena we e also epo ed (Al-Ta azi, 2000; Klinge e al., 1999). Bas a e al. (1996) men ioned ha a sunami 3–4 m high hi Nuweiba ha bo . The sou ce pa ame e s o he Nuweiba ea hquake ha e been de e mined by se e al independen s udies (Klinge e al., 1999; Bae e al., 2008 and e e ences wi hin), which allows nume ical simula ions o he sunami p opaga ion. The nume ical modelling o sunami p opaga ion is a ela i ely well es ablished me hodology which has been alida ed agains eco ded da a om his o ical e en s o e he wo ld (Choi e al., 2008; Alasse e al., 2006; Ioualalen e al., 2010; Pe iáñez and Ab il, 2013, 2014a). The main agen s igge ing sunamis a e ea hquakes by geological aul s, subma ine and sub-ae ial landslides, en y o py oclas ic flows and calde a collapse in olcanoes. Reliable modelling s a egies ha e been de eloped o all o hem (Iglesias e al., 2011; No iko a e al., 2011; Okal e al., 2011; Pe iáñez and Ab il, 2014a). As a as we know, sunami modelling wo ks ha e no been p e iously conduc ed in he Red Sea a ea. This pape is aimed a s udying he sunami p opaga ion in hese wa e s by adap ing p e- iously es ed nume ical ools. The cha ac e iza ion o he sou ce pa ame e s o he 1995 Nuweiba ea hquake, along wi h he sca ce desc ip ion o he sunami effec s (as abo e commen ed) p o ide a minimum basis o suppo ing a modelling exe cise. F om he a ailable s udies on he seismici y in his a ea, i is possible o cons uc hypo he ical sunamigenic sou ces by handling he known ocal pa a- me e s, namely he epicen e and aul angles. Simila ly, om he known main ea u es o he olcanism and sal flows, i is possible o buil hypo he ical scena ios o he en y o py oclas ic flows, o calde a collapse and subma ine landslides. These nume ical exe cises a e expec ed o p o ide some insigh on he main ea u es o he sunami p opaga ion in his ma ine sys em, which exhibi s a qui e singula geome y. Resul s can allow he assessmen o egional exposu e. Thus, he Red Sea and he gul s o Aqada and Suez con o m long and na ow open basins o which undamen al pe iods o se e al hou s (wi hin he ange o hose o he main idal cons i uen s) a e expec ed (Rabino ich, 2009). S udying e en ual wa e amplifica ion and esonance effec s may be o pa icula in e es o he main ci ies in he coas al a ea, and o assessing he po en ial isks o he Suez 2 he domain excep o hose a eas affec ed by he de o ma ion in he ee su ace induced by olcano calde a collapse, o by subma ine ea hquakes igge ed by geological aul s. Fo sunamis p oduced by ea hquakes in geological aul s, he sea- floo de o ma ion p oduced by he ea hquake is compu ed using he classical Okada o mulae (Okada, 1985). Inpu s o his equa ion a e aul plane s ike, ake, dip, slip, loca ion, leng h and wid h, as well as seismic momen and igidi y. The s anda d p ocedu e assumes ha such de o ma ion is ins an aneously ans e ed o he ee wa e su ace, and i is imposed as he ini ial condi ions o he nume ical simula ion (see, o ins ance, Ioualalen e al., 2010; Ab il e al., 2013). Due o he explo a o y cha ac e o his s udy, he simples app oach by Ha bi z (1992) and Cecioni and Bello i (2010) has been adop ed o simula e sunamis igge ed by subma ine landslides. The slide can be desc ibed as a solid body whose downslope mo emen locally modifies he ba hyme y and induces changes in he le el o he o e lapping wa e s, which p opaga e as g a i y wa es. The adop ed geome y is a box o leng h L, wid h Band maximum hickness h Δ , and wi h an exponen ial smoo hing o e a dis ance Sin he on and ea and B / 2 on he flanks. The esul ing olume is V BhL S= 0.90 Δ ( + 0.90 ) (Ha bi z, 1992). The maximum eloci ies and du a ion o he displace- men can be es ima ed om he slope, maximum heigh and ic ion and d ag coefficien s (Ha bi z, 1992). The wo-slope kinema ic model by Pe iáñez and Ab il (2014a) has been adop ed. Applica ions o his model can be ound in such e e ence and in Ab il e al. (2013),Ab il and Pe iáñez (2015). Tsunamis gene a ed by a py oclas ic flow in o he sea can be modelled as a pa icula case o a subma ine landslide in which he ini ial leng h o he slide is ze o and i inc eases in ime as he py oclas ic flow is en e ing he sea. The high ini ial eloci y, U o , dec eases o ze o as he flow comple es a displacemen R 2 . These pa ame e alues can be es ima ed ollowing he me hodology by No iko a e al. (2011). Applica ions o his model can be ound in his e e ence and in Pe iáñez and Ab il (2014a). Fo modelling a olcano calde a collapse, he me hodology by No iko a e al. (2011) has been adop ed. The ini ial wa e le el co esponds o he dep h o he calde a o med. Thus, he ini ial wa e displacemen is nega i e (i.e., downwa ds). Al e na i ely, he o mula desc ibed by To s ik e al. (2010) o unde -wa e explosions could be used. 2.2. Tsunamingenic sou ces in he Red Sea 2.2.1. The 1995 Nuweiba Ea hquake ( M =7. 3 w ) The Gul o Aqaba lies a he sou he n segmen o he Dead Sea Faul (DSF) sys em. I is 180 km long and 10–25 km wide, esul ing om he succession o h ee pull-apa basins: he Daka Deep, he A agonese Deep and he Ela Deep. Dep hs wi hin he gul each 1800 m deep in places, and i is su ounded by he high moun ain anges o Sinai and Hedjaz. The M w 7.3 1995 Aqaba ea hquake is he la ges ins umen ally eco ded ea hquake along he DSF (Klinge e al., 1999). A desc ip ion o i s effec s on he coas al a eas o he Gul o Aqaba and he ci ies o Aqaba, Eila and Nuweiba can be ound, among o he s, in he wo k by Klinge e al. (1999), and hey ha e been summa ized in he In oduc ion sec ion. These au ho s epo ed small sunami wa es a Aqaba and Eila . Men ion o high sunami wa es, up o 3–4 m in he Nuweiba ha bo is ound in he wo k by Bas a e al. (1996), as epo ed by Salem (2009). The epicen e o he ea hquake was offsho e. The sou ce pa a- me e s ha e been s udied by diffe en au ho s based on seismology and InSAR me hods, as summa ized by Bae e al. (2008). These au ho s p o ided he mo e upda ed es ima ion in ol ing a single e en wi h a a iable slip o 0–3 m. Thei esul s, wi h he maximum slip alue o 3 m ha e been used o define he sou ce F1 in his s udy (Table 1). Klinge e al. (1999) sugges ed a sequence o h ee e en s, wi h 2.5 m slip o he la ges one, bu wi hou quan i ying he aul wid h. Sou ce F1b in Table 1 is a e sion o F1 wi h his lowe slip alue. The su ace de o ma ions, es ima ed om he o mula o Okada (1985) lead o a Fig. 1. Compu a ional domain o he 2D simula ions wi h a spa ial esolu ion o 60 s o a c. The squa e delimi s a highe esolu ion domain which uses 30 s o a c. Dep hs a e aken om GEGCO08 and GEODAS da abases. Scale colo -ba in m, measu ed posi i e below he p esen sea le el. Table 1 Faul pa ame e s used in simula ions. Geog aphical coo dina es co espond o he aul cen e . Re e ences: [1] Bae e al. (2008) [2] Klinge e al. (1999),Bae e al. (2008). Hypo he ical aul s based on ocal mechanisms o eco ded ea hquakes and imposed alues o leng h, wide and slip: [3] Mohamed e al., 2015; e en s 1–2004 ( hei Table 2) and 3–2006 ( hei Table 3); [4] Fos e and Jackson (1998) e en s 670313, 771228 and 930313 and 800114, wi h uned pa ame e s; [5] This is a pu e syn he ic sou ce. Fo he hypo he ical aul s he ake angle has been uned o ze o in he applica ion o he Okada o mula o enhance he e ical displacemen . Tsunami ϕ E °λ N Leng h (km) Wide (km) Slip (m) S ike (°) Dip (°) Rake (°) Re e ence F1 (Nuweiba 1995) 34.75 28.97 58.5 30.0 3.0 197.5 67.0 −4.0 [1] F1b (Nuweiba 1995) 34.75 28.97 58.5 30.0 2.5 197.5 67.0 −4.0 [2] F2 (Gul o Suez) 33.10 28.47 50.0 20.0 8.0 308.0 53.0 −63.0 [3] F3 (Sou h Sinai) 34.62 27.39 80.0 30.0 8.0 125.0 52.0 −69.0 [3] F-RS1 (670313) 38.75 19.68 160.0 60.0 10.0 309.0 45.0 −100.0 [4] F-RS2 (771228) 40.28 16.66 120.0 40.0 10.0 106.0 66.0 −171.0 [4] F-RS3 (930313) 38.85 19.67 180.0 80.0 12.0 144.0 40.0 −84.0 [4] F-RS4 (800114) 40.34 16.52 200.0 90.0 14.0 24.0 30.0 −9.0 [4] F-RS5 34.62 27.35 150.0 60.0 14.0 125.0 52.0 0.0 [5] 3 Fig. 2shows wo snapsho s wi h he compu ed ins an aneous wa e su ace ele a ions 15 and 60 min a e he 1995 Nuweiba ea hquake using he sou ce pa ame e s F1 (Table 1). Along he deepes cen al axis o he Gul , he speed o g a i y wa es can su pass 450 km/h. Al hough i is lowe in he shallowe coas al a eas, in his na ow wa e body he sunami signal eaches Nuweiba and Haql in less han h ee minu es (Fig. 3), and a e se en minu es i is pe cei ed a Aqaba. The eflec ed wa es hen p oduce mul iple in e e ences wi hin he gul , and he sea becomes s o my. Fig. 3 shows he compu ed ime se ies o wa e ele a ions o fi e selec ed loca ions along he gul sho eline ( hey a e labelled in Fig. 2). The fi s wa e a Aqaba, a he no he n eaches o he gul , has an ampli ude o 0.8 m (0.7 when using he al e na i e sou ce F1b om Table 1). Then, wa e s ecede and a new se ies o wa es hi he sho eline a in e als o oughly 30 min. A Nuweiba, he fi s wa e is 1.5 m heigh (1.3 wi h sou ce F1b). A his loca ion he maximum ange be ween high and low wa e le els eaches 2.9 m. The sunami signal is noisie , wi h high equency cons i uen s, bu as ime goes on, he ∼30 min pe iod becomes dominan . A simila end is obse ed in Haql, in he eas e n sho e o he Gul o Aqaba, bu wi h a maximum ampli ude o 0.6 m, and wi h a highe con ibu ion o high equency cons i uen s. The sunami signal in Nabq, close o he gul mou h, is smoo he , simila in ampli ude o ha o Haql, and bo h end o un in phase. The signal a She m, a sou he n Sinai and ou o he Gul o Aqaba, has a maximum ampli ude o only 7 cm. Fig. 4 shows he compu ed maximum ampli ude o wa e ele a- ions and wa e cu en s 6 h a e he 1995 Nuweiba ea hquake. Ampli udes o 1 m can be encoun e ed in he wes e n sho e o he Gul , a ound he a ea o Nuweiba, and in he opposi e eas e n coas s, being he las di ec ly affec ed by he ini ial seafloo de o ma ion. Mode a ely high ampli udes (o e 0.8 m) a e ound in he no he n a ea o he Gul and in some sca e ed embaymen s. Ou o he Gul o Aqaba he impac o he sunami is e y week. As seen in he same figu e, wa e cu en s o e 0.4 m/s a e ound only along ew coas al a eas and in he sou he n gul . Those land g id-cells ha a any ime become flooded by he sunami appea as open ed ci cles in Fig. 4 ( he size has been exagge a ed). The e a e only 10 places, which co espond o coas al a eas wi h mean land ele a ion a ound 1 m abo e sea le el. They a e flooded by wa e laminae wi h hickness anging om 0.1 up o 1.1 m. I is wo h no ing ha ides in he Gul o Aqaba ha e an ampli ude o he o de o 0.6 m, wi h su ace wa e cu en s ha a ely su pass 20 cm/s (Monismi h, 2004; Ahmed e al., 2012), Al hough wi h a s o my sea, he cha ac e is ic pa e n o s anding wa es eme ged along he gul axis. Nodal lines which sepa a e a eas wi h high and low wa e le els (Fig. 2) appea wi h a configu a ion close o node n=2 o an open-mou h ec angula basin ( L λ=T 5 4, whe e λ T is he wa eleng h o he sunami; see Rabino ich, 2009). Thus, wi h he known alues o he leng h o he Gul o Aqada (L=180 km) and i s axial dep h (H∼1800 m), i is possible o es ima e a pe iod T ∼0.5h 2 ( T Ln gH=4 /[(2 +1) ] n ;Rabino ich, 2009). The ime se ies in Fig. 3 we e used o e alua e he powe spec al densi y (p opo ional o he ene gy spec al densi y) om FFT analysis (Sahal e al., 2009; Pe iáñez and Ab il, 2014b). Resul s a e shown in Fig. 5 o ou o he selec ed loca ions. A majo peak appea s in all cases o a pe iod o 0.55 ± 0.05 h ( he ange co esponds o hal he ime window esol ed by he applied Ma lab FFT algo i hm, as in Pe iáñez and Ab il, 2014b), which compa es well wi h he p e ious es ima e. A pe iod o 1.0 ± 0.2 h is well esol ed in Aqaba and Naql si es, which fi s o he heo e ically es ima ed alue o T ∼0.9h 1. A pe iod o 0.38 ± 0.02 h is obse ed a h ee o he si es, which co esponds o T ∼0.4h 3 . A Nuweiba he sunami signal has a high in ensi y, and i is possible o sol e he pe iod 0.30 ± 0.2 h (T 4 ). The undamen al pe iod T ∼2.7h 0is obse ed in all he cases, al hough wi h a poo e esolu ion. maximum (g a i a ional po en ial) ene gy o he igge ed sunamis o 1.24 and 0.86 k (1 k =4.18×10 12 J) o F1 and F1b, espec i ely. 2.2.2. Sou ce pa ame e s o hypo he ical sunamis igge ed by subma ine ea hquakes Table 1 epo s aul pa ame e s o a se o se en sunamigenic sou ces used in simula ions. Epicen e and aul angles a e based on he seismici y s udies epo ed by Mohamed e al. (2015) -e en s 1– 2004 and 3–2006, and Fos e and Jackson (1998) - e en s 670313, 771228, 930313 and 800114. This selec ion o sou ces is linked o he majo ea hquakes e en s and i co e s he main seismic zones wi hin he s udied domain. The alues o leng h, wid h and slip ha e been imposed wi h he c i e ia o gene a ing ene ge ic e en s able o p opaga e o e la ge a eas wi hin he Red Sea. In o de o enhance he e ical displacemen , he ake angle has been uned o ze o deg ees in he applica ion o he Okada o mula. Sou ces F2 and F3 ha e been simula ed wi h he 30-seconds esolu ion mesh, and sou ces F-RS1 o F-RS5 wi h he 1-min esolu ion mesh. 2.2.3. Tsunamis igge ed by py oclas ic flows and calde a collapse The Jebel a Tai olcano has been selec ed as he scena io o hese sunamigenic sou ces. The olcanic island has an ellipsoidal shape wi h a majo diame e o 4.4 km. The e up ion e en o Sep embe 2007 has been well desc ibed by Xu and Jónsson (2014). I expelled 2.2×10 7 m 3 o la a wi h wo main flows in he E-NE and W-SW di ec ions. He e we explo e he effec s o a mo e se e e e up ion, p oducing a py oclas ic flow wi h a o al olume o 5.4 km 3 , en e ing in o he sea a he no he n a ea o he Jebel a Tai olcano. The flow is 3.6 km wide ( ∼2Δx ), a hickness o 60 m, and i is di ec ed o 323° (measu ed clockwise om he No h). Following he modelling app oach by No iko a e al. (2011), he ini ial eloci y o he flow was es ima ed as 68 m/s, and i s du a ion was 0.32 h. The Jebel a Tai ises on a opog aphic low in he Red Sea Ri . The on o he flow would be cap u ed wi hin his geological bowl, comple ing a maximum un-ou dis ance o 25 km. A sinus unc ion has been adop ed o he a enua- ion o he flow speed. This scena io can be compa ed wi h hose epo ed by No iko a e al. (2011). Thus, he o al olume o py oclas ic flow in he 1883 K aka au e up ion was 20 km 3 wi h a maximum eloci y o 150 m/s and a hickness o 20 m. These magni udes ook alues o 20 km 3 , 200 m/s and 80 m o he 1815 Tambo a e up ion. The calde a collapse is assumed o be p oduced in he no he n a ea o he olcanic island, wi h a o al olume o 5.0 km 3 and a mean deple ion dep h o 250 m. This figu e can be compa ed wi h he 19– 34 km 3 collapse modelled by No iko a e al. (2011) o he La e B onze Age e up ion o The a. 2.2.4. Tsunamis igge ed by subma ine landslides Two hypo he ical mass was ing e en s ha e been conside ed, loca ed a he on o wo sal flow lobes iden ified by Feldens and Mi chell (2015) in he The is Deep and he A lan is II Deep ( hei egions C and D, espec i ely). F om he de ailed elie image o mul ibean da a i is possible o ex ac ealis ic alues o he on posi ion, opog aphic slopes, slide wid h, unou dis ance and di ec ion o displacemen , which a e comple ed wi h es ima es o leng h, smoo hing dis ance, and maximum hickness o gene a e sunamigenic e en s in ol ing 21.0 and 26.5 km 3 , espec i ely. Table 2 summa ies he geome ic and kinema ic pa ame e s o his wo subma ine landslides. The slide SL2 is a e sion o SL1 wi h a la ge unou dis ance. 3. Resul s and discussion 3.1. The 1995 Nuweiba ea hquake 4 3.2. Hypo he ical scena ios o sunamis in he Red Sea 3.2.1. Tsunamis igge ed by subma ine ea hquakes in geological aul s The sunami F2 (Table 1) occu s in he cen al Gul o Suez, whe e he seafloo de o ma ion injec s 7.7 k in o he wa e column as ini ial po en ial g a i a ional ene gy. Fig. 6 shows he compu ed maximum ampli udes o wa e ele a ions and wa e cu en s a e a simula ion ime o 6 h. Wa e ele a ions su pass 3 m in he a ea o e he geological aul and hey p oduce no iceable flooding in he adjacen sho eline, wi h unups o e 3 m (yellow ci cles in his figu e) and wa e cu en s o e 1 m/s. The impac o he sunami dec eases no hwa ds, bu an amplifica ion phenomena is obse ed a ound he Po o Suez whe e he coas al zones a e flooded wi h a wa e laminae o some 0.5 m. Sou h o he sou ce a ea he ampli udes and eloci ies a e also high, pa icula ly along he eas e n sho eline. The sunami impac s a e negligible ou o he Gul o Suez. Faul F3 (Table 1) is loca ed sou heas o he Sinai Peninsula, and he associa ed sunami has an ini ial ene gy o 18.8 k . I shows a high di ec ionali y no mal o he aul s ike. In he di ec ly impac ed coas s, his sunami p oduces unups o e 3 m (Fig. 7). High wa es p opaga e along he sho elines, p oducing floods o e 1.0 m a many places. Compu ed ime se ies o wa e ele a ions a some selec ed loca ions a e sunamis F2 and F3 a e shown in Fig. S-1, in Elec onic Supplemen a y Ma e ial (ESM). Figs. 8 and 9show he compu ed maximum ampli udes o wa e ele a ions and cu en s o he wo mos ene ge ic ea hquakes, F-RS3 and F-RS4 (Table 1), wi h ini ial ene gies o 300 k and 550 k , espec i ely. Tsunami F-RS3 p oduces high wa e ampli udes in a wide band o he Cen al Read Sea sou h o he line defined by he ci ies o Sudan and Yidda, whe e he coas al a eas a e flooded wi h unups o e 3 m. Ele a ions o e 1 m p opaga e along he sho elines flooding a eas wi h low opog aphic ele a ion. An amplifica ion phenomena is ob- se ed in he no he n sho eline o he main basin and in he Gul o Aqaba, wi h wa e ele a ion ampli udes a ound 0.8 m. This sunami induces s ong cu en s in he shallow and ela i ely dis an a eas o he Fa asan Islands and he Dahlak A chipelago. Tsunami F-RS4, has i s epicen e in he Sou he n Red Sea, a only 20 km om he no he n Dahlak A chipelago, and 150 km om he Fa asan Islands. Thus, i s ongly impac s hese a chipelagos, whe e i p oduces high wa e cu en s and no iceable floods. A Massawa, he fi s wa e is 2.4 m high. No h o Sudan wa e ele a ions a e negligible, al hough an amplifica ion effec appea s again in he Gul o Aqaba, wi h ampli udes o e 0.5 m. Wa e cu en s o 0.15–0.20 m/s un along mos o he sho eline o he Red Sea. The e is a sligh amplifica ion a he en ance o he Gul o Suez. Tsunami F-RS2 (no shown) has he same epicen e han F-RS4, bu diffe en geome ical and ocal pa ame e s. I s ini ial ene gy is 39.2 k , which is mos ly dissipa ed a ound he sou ce a ea and in he eas e n edge o he adjacen i . Some flooding appea s along he no he n Dahlak A chipelago and in nea by sho e o E i ea. Table 2 Sou ce pa ame e s o hypo he ical sunamis igge ed by subma ine landslides in cen al Red Sea. They a e de ined as in Ha bi z (1992) wi h kinema ics a e Pe iáñez and Ab il (2014a). The slide olume is V BhL S=0.9 Δ ( +0.9 ) ;B, wid h; L, leng h; S, smoo hing dis ance; hΔ , maximum hickness. Slide di ec ion is measu ed clockwise om he no h. The posi ion e e s o he ini ial on loca ion. Landslide Geome ical pa ame e s Posi ion Di Kinema ics L(km) S(km) B(km) Δh (m) V(km 3 )ϕ E °λ N °θ°R 1 (km) α 1 (°) U max, 1 (m/s) R 2 (km) α 2 (°) U max, 2 (m/s) SL1 9.0 3.0 10.0 200 21.0 37.819 22.444 245 4.5 6.0 50.0 4.5 1.8 37.8 SL2 9.0 3.0 10.0 200 21.0 37.819 22.444 245 6.0 5.0 50.0 10.0 1.8 37.8 SL3 12.0 3.0 10.0 200 26.5 38.280 20.572 190 7.5 4.5 50.0 7.5 4.5 50.0 Fig. 2. Compu ed ins an aneous wa e su ace ele a ions 15 and 60min a e he 1995 Nuweiba ea hquake (sou ce pa ame e s F1 in Table 1). 5 Figu es S-2 and S-3 (in ESM) show he compu ed maximum ampli ude o wa e ele a ions and wa e cu en s o sunamis F-RS1 and F-RS5, espec i ely. Thei ini ial g a i a ional po en ial ene gies we e 130 k and 215 k , espec i ely. F-RS1 gene a es high wa e ele a ion ampli udes in he Cen al Red Sea, and high wa e cu en s which un along he sho elines, flooding a eas a ound Yibdda and Po Sudan (Fig. S-2). The sunami F-RS5 s ongly impac s all he egions in No he n Red Sea and p oduces unups o e 1.0 m along he sho eline down o Yibdda and Po Sudan (Fig. S-3). The o al olume o seawa e flooding he coas al a eas can be es ima ed by mul iplying he maximum wa e heigh a each flooded g id-cell by i s su ace. I was (in km 3 ) 0.011, 0.005, 0.150, 0.330, 2.215, 0.391, 4.447, 3.449 and 3.691 o sunamis F1, F1b, F2, F3, and F-RS1 o F-RS5, espec i ely. A linea co ela ion can be es ablished a 99% confidence le el be ween flooded olume and ene gy o his se o sunamis igge ed by subma ine ea hquakes wi h ene gies up o 300 k (e.g., excluding F-RS4). The fi ed pa ame e alue o he slope was o 0.0157 ± 0.0006 km 3 /k . This is an empi ical ela ionship which Fig. 3. Compu ed ime se ies o wa e ele a ions a fi e selec ed loca ions (see map in Fig. 2) a e he 1995 Nuweiba ea hquake. Fig. 4. Compu ed maximum ampli ude o wa e ele a ion and wa e cu en s due o he 1995 Nuweiba sunami. Red open ci cles co espond o hose coas al a eas being flooded by a wa e laminae wi h hickness anging om 0.1 up o 1.1 m. 6 holds o he s udied domain and o his pa icula se o sunamis. I can be used wi h ca e, along wi h he sunami dispe sion pa e ns shown in he p e ious figu es, o ge a fi s p oxy o he po en ial sunami impac s. 3.2.2. Tsunamis igge ed by py oclas ic flows and calde a collapse As he py oclas ic flow en e s in o he sea i ans e s po en ial and kine ic ene gy o he wa e column. A peak ene gy o 240 k is achie ed a e 7 min. La e ene gy dissipa ion becomes dominan . The flow descends owa ds a opog aphic low whe e i is apped. Thus, he igge ed sunami p oduces a a he local impac . High alues o wa e cu en s a e ound in he shallow a eas o he su ounding a chipela- gos, whe e some flooded si es also appea (Fig. 10). The o al olume o seawa e flooding he coas al a eas was 0.622 km 3 , six imes lowe han he expec ed om a ea hquake- igge ed sunami wi h equi alen ene gy. The calde a collapse igge s a sunami wi h an ini ial ene gy o 1.5 M , bu i s effec s emain cons ained o he Sou he n Red Sea and hey a e compa able o hose p oduced by he en y o py oclas ic flows (Fig. 11). Indeed, he o al flooded olume was 0.434 km 3 . 3.2.3. Tsunamis igge ed by subma ine landslides Subma ine landslides a e e y ene ge ic e en s. The sunamis igge ed by SL1 (Table 2) ans e s a peak ene gy o 390 k o he ocean. I is only sligh ly highe o SL2 (400 k ), which has a la ge unou dis ance. The sunami SL3 is e en mo e ene ge ic, wi h a peak ene gy o 1.0 M . These simula ed sunamis show a s ong di ec ion- ali y and a he local impac s (Figs. 12 and S-4 -in ESM). Thus, o SL3 mos o he sunami ene gy is di ec ed owa ds he coas a ound Po Sudan, whe e a no iceable flooding is p oduced. A his loca ion he fi s wa e eaches 4.9 m high. Flooding is also p oduced in he opposi e sho eline, a ound he si e o Yidda (see Fig. S-4, ESM). The o al flooded olumes we e (in km 3 ) 0.260, 0.325 and 1.415 o landslides SL1 o SL3, espec i ely. They a e one o de o magni ude lowe han hose expec ed om ea hquake- igge ed sunamis wi h equi alen ene gy. 3.3. Spec al analysis The ene ge ic e en s F-RS1, F-RS4 and F-RS5, wi h epicen e s in he Cen al, Sou he n and No he n Red Sea, espec i ely, ha e been used o gene a e ime se ies o wa e ele a ions o a se o 15 syn he ic gauges dis ibu ed along he sho eline (gi en in Table 3 and depic ed in Figs. 4 and 9). The ime se ies co e a e 24 h long wi h a ime s ep o 2 s. They se ed o e alua e he powe spec al densi y om FFT analysis and o iden i y he pe iods o he majo cons i uen s (Pe iáñez and Ab il, 2014b). Resul s a e shown in Fig. 13 o all loca ions in Table 3. The h ee sunamis a e able o exci e a low equency cons i uen wi h pe iod 8 ± 2 h in mos o he places. Pe iods o 4.8 ± 0.4 h and 3.0 ± 0.3 h a e also ubiqui ous. These figu es oughly fi he ha monic sequence wi h n=1,2,3 om a model o a ec angula open-mou h basin wi h leng h ∼2000 km and uni o m dep h ∼1150 m ( T Ln gH=4 /[(2 +1) ] n ;Rabino ich (2009)). The undamen al pe iod o ∼21 h canno be esol ed wi h his nume ical expe imen . Fo he sake o compa ison, Fig. 13 plo s he pe iods p edic ed by his simple model o n =1− 5 and n=9. High equencies (low alues o pe iods) Fig. 5. Compu ed powe spec al densi y (using FFT) om ime se ies o wa e ele a ions ( Δ =1.0 s; ime-se ies leng h 6 h) a a se o selec ed loca ions (see Fig. 2). Fig. 6. Compu ed maximum ampli ude o wa e ele a ion and wa e cu en s due o he F2 sunami (Table 1). Those land g id-cells flooded wi h unups in he ange o 1–3 m and highe han 3 m a e depic ed as open ed and yellow ci cles, espec i ely ( he size o he ci cles has been exagge a ed). 7 a e exci ed only in places ela i ely close o he ea hquake epicen e . The deep Gul o Aqaba (gauges 1–2) ollows he end o he main Red Sea basin, while he shallow Gul o Suez (gauges 4–5) shows a diffe en beha io . In his case only hose eigenmodes which a e close o he equencies o he main basin a e exci ed. 3.4. Discussion on sunami haza ds in he Red Sea The 1995 Nuweiba ea hquake has been he la ges ins umen ally eco ded ea hquake along he DSF. Despi e he p oximi y o he epicen e , majo damages in Nuweiba we e due o he di ec effec s o he ea hquake, wi h li le o null e e ence o sunami wa es. The Aqaba and Suez gul s a e long and na ow wa e -bodies. Tsunami wa es each he sho eline quickly, whe e hey dissipa e mos o he ene gy. This limi s any po en ial long dis ance effec s. The same is applicable o he main Red Sea basin. The ew his o ical sunami e en s eco ded in he las millennium e e o some a he local impac s. The 12 po en ial sunamigenic sou ces conside ed in his s udy include e en s wi h diffe en peak ene gies, bu all o hem a e one o wo o de s o magni ude mo e ene ge ic han he 1995 Nuweiba sunami. Al hough linked o po en ial sunamigenic sou ces (subma ine ea hquakes, landslides and olca- nos) hei p obabili y o occu ence canno be assessed om his o ical eco ds, al hough i can be guessed as e y low. Fig. 7. As Fig. 6, bu o he sunami F3 (Table 1). Fig. 8. As Fig. 6, bu o sunami F-RS3 (Table 1). 8 Tsunamis igge ed by subma ine ea hquakes p oduce highe impac s in he sho eline han he se o s udied e en s igge ed by subma ine landslides, en y o py oclas ic flows and olcano calde a collapse. The linea ela ionships ound be ween peak ene gy and o al flood olumes o he fi s g oup, along wi h he maps wi h he spa ial dis ibu ions o maximum wa e ele a ion and cu en ampli udes, can Fig. 9. As Fig. 6, bu o sunami F-RS4 (Table 1). Fig. 10. Compu ed maximum ampli ude o wa e ele a ion and wa e cu en s due o he en y o 5.4 km 3 o py oclas ic flow (see ex ). Flooded a ea a e depic ed wi h he same c i e ia as in Fig. 6. 9