open and almost shut case for explosive eruptions vent processes determined by so2 emission rates at karymsky volcano kamchatka vent processes were examined at karymsky volcano kamchatka by measuring so2 emissions using a correlation spectrometer cospec continuous high sensitivity cospec measurements and physical observations were collected on 11 and 12 september 1999 when karymsky was producing small ashy eruptions every 5 20 min each eruptive event began with an explosion and audible rumbling lasting 30 s followed in some cases by audible chugging lasting to 2 min gas plumes accompanied each event and almost without exception the plumes dissipated and became invisible despite significant so2 emissions variations in so2 output show distinctive patterns that correlate with eruption activity maximum so2 output occurred following each explosion and then declined rapidly to low but detectable levels in contrast a second type of event often associated with audible chugging was characterized by high so2 output long after the initial ash blast variations in degassing at karymsky can be explained by secondary boiling gas pressure accumulation and vent resealing we developed a new application of the cospec technique to study the dynamic vent processes of erupting volcanoes this application provides insights into the processes that occur at the otherwise inaccessible vents of erupting volcanoes particularly when a volcano changes from passive degassing and small explosions to degassing patterns that may precede a larger and more dangerous eruption

the arcs of the western alps and the northern apennines an updated view abstract the arcs of the western alps and the northern apennines and the link between them are in the process of being investigated using the european geotraverse and they have historically been interpreted in many different ways new information particularly geophysical further constrains possible models both arcs have evolved in several stages sometimes complexly interrelated and sometimes independent of each other compressional belts produced in these stages have either been of the push arc type indentation into a deformable mass or the pull arc type backward migration of hinge of a subduction zone leading to small extensional basins known as back arc basins and pores with an arcuate mountain range on the subduction side extensional periods with the possible formation of pull arcs in the alps comprise the gosau period between the eo and meso alpine push arc phases and the oligocene lull period between the meso and the neo alpine push arc phases in the northern apennines remainders of the meso alpine nappes were involved in oligocene early miocene pull arc formation associated with spreading in the balearic sea followed by push arc formation particularly in the middle miocene and by renewed pull arc formation from the latest late miocene to the present during all of these developments the moho was modified by such processes as lithospheric stretching asthenospheric intrusions subhorizontal shearing and isostatic uplift the present moho configuration is consequently a collage of moho patches formed at different intervals both push and pull arcs are laterally bounded by complementary strike slip or transform zones these too were modified in the course of history and their final geometry is consequently of a very complex nature in the alps for instance the insubric fault zone appears to have been the main dextral transform fault of the neogene push arc until it was sinistrally kinked by the giudicarie fault zone and probably deactivated dextral transpression being briefly transferred to the en echelon brachyanticlines of the late alpine windows in the case of the oligocene apennines the sinistral rotations of corsica and sardinia otherwise hard to understand may be attributed in part to sinistral transform motions along the eastern border zone of the oligocene early miocene balearic extension

joining up land and marine seismic data case study from procida and ventotene islands tyrrhenian sea italy abstractthe seismic refraction survey routinely used to obtain information on subsurface geology has a limited use in the foreshore zone we have evaluated a nonstandard approach to acquire seismic data in the backshore foreshore area joining up land and marine seismic data the innovative part was the acquisition of a continuous seismic profile that allowed the recording of high resolution data in a transition zone tz to establish an integrated approach for improving the land marine seismic model in areas characterized by a complex near surface geology to achieve this objective two seismic tests were carried out along the beaches of the tyrrhenian islands of procida and ventotene we defined the p wave vp and s wave velocities vs with depth by integrating the tomography of the refracted first arrivals vp velocities versus depth with the inversion of the phase velocities dispersion curves extracted from the surface waves 1d vs velocities models working with both seismic methods allowed us to o

arguments for the pre rift uplift and rift propagation in the ligurian provencal basin northwestern mediterranean in the light of pyrenean provencal orogeny the cenozoic provencal orogeny and the subsequent opening of the ligurian provencal basin were caused by a geodynamic mechanism that originated in the cretaceous it is evident from the arguments presented that 1 regional doming preceded rifting of the continental margin and this uplift widened and or migrated during the ensuing opening of the ligurian provencal basin 2 clastic sedimentation on the provencal platform was initiated during the early cenomanian 3 deformation in the provencal block which varies from late cretaceous to miocene reflects a migration of the north south compression from west to east accross the block 4 the languedoc provencal fold belt was initiated during the eocene as a result of tectonic uplift and sinistral displacement of the paleozoic basement toward the north significant geologic features of the region associated with these events include 1 similarities in shape of the languedoc virgation and the provencal thrust front with the shape of geophysical features over the golfe du lion 2 the unusual width of the young stretched continental margin in the golfe du lion 3 the distinctive v shaped form of the ligurian oceanic crust and 4 the concordance in age of the earliest post rift deposits which increasingly young toward the east and magnetic anomalies that parallel the basin axis these events and structures are attributed to the uplift of a paleozoic block situated to the south in the golfe du lion and previously buried under the mesozoic cover the development of this crustal uplift since upper aptian and its northeastwards migration and or gradual widening account for both sedimentary events and tectonic deformation that occurred on the provencal platform until upper eocene and the later stage of rifting and formation of the provencal margin in the ligurian provencal basin the synthesis of marine data as well as relevant terrestrial data indicates that rifting propagated towards the gulf of genoa while the corsica sardinia block rotated to the southeast

new data and hypothesis on the development of the tyrrhenian basin abstract among those basins which developed during the neogene and quaternary at the rear of the perimenditerranean mountain chains the tyrrhenian basin is the most recently formed comparing the available geological and geophysical data the tyrrhenian domain and its neighbourhoods can be divided into more or less homogeneous sectors namely northern and southern tyrrhenian apenninic chain maghrebides chain apulian and iblean african foreland ionian foreland for each sector the different phenomena involved and the crustal characteristics are discussed the evolution of the domain has been explained by the application of a crustal stretching model developed for continental margins this approach predicts the formation of basinal areas as a result of the europe africa collisional movements within a plastic rigid deformation model taking into account the mass redistribution after collision the model explains both the distension developed within the collisional system and the penecontemporaneous development of compressive and distensive phases as a consequence of the intraplate stresses horizontal shearings affecting the whole lithosphere at different levels occur with delaminations asthenosphere uprising and gradual collapse in the upper crust e w trending and strike slip dextral faults played a primary role in the evolution of the tyrrhenian basin inducing the largest tearings at the end of the major transcurrent systems such an evolution is complicated by the migrating motion of the shear zone from n to s and by the penecontemporaneous stop in the extension from the northern towards the southern domains of outstanding importance is the shear zone which borders the southern tyrrhenian enabling the opening of the basin and allowing the development of the major group of en echelon sub basins with a nw se trend

types of crust beneath the ligurian sea the structural setting beneath the ligurian sea resujts from several tectonic events reflected in the nature of the crust the central western sector called the ligurian basin is part of the northwestern mediterranean it is a marginal basin that was generated in oligocene miocene time by subduction of the adriatic plate beneath the european plate and by the eastward drift of the corsica sardinia block the eastern sector belongs to the tyrrhenian basin system and is characterized by extensional activity which since tortonian time superimposed an earlier compressional regime our effort has been addressed in particular towards simplifying the complex nature of the crust of the ligurian basin by modelling its genesis using uniform extension and sea floor depth variation with age in the rift stage of the basin s evolution the initial subsidence reaches the isostatic equilibrium level of the asthenosphere by a thinning factor of 3 15 the additional passive process corresponding to the cooling of the lithosphere since 21 ma leads to a total tectonic subsidence of 3 4 km representing the boundary of the extended continental crust for values up to 4 1 km a transitional type crust is expected whereas for higher tectonic subsidence values a typical oceanic crust should exist after setting these constraints the boundaries of the different crust types have been drawn based on total tectonic subsidence observations deduced from bathymetry and post rift sediment thickness although there is a general agreement with the previous reconstructions deduced from other experimental data the oceanic realm has wider extent and more complex shape the northernmost part of this realm shows crust of sub oceanic type altemating basement highs with lower subsidence values the observed surface heat flux is consistent with the predicted geothermal held in the alpine provencal continental margin and in the oceanic domain however a characteristic thermal asymmetry is clearly visible astride the basin due to the enhanced heat flux of the corsica margin even if the uniform extension model accounts well at a regional level for the present basement depth a remarkable tectonic subsidence excess has been found in the alpine provencal continental margin this evidence agrees with the reprise in compression of the margin the direction of the greatest principal stress is n120 e on average

why is the ligurian basin mediterranean sea seismogenic thermomechanical modeling of a reactivated passive margin 1 the seismic activity of the ligurian basin the northeastern termination of the western mediterranean basin is larger than in surrounding regions even though recent geodetic studies attest that this area is subject to very low levels of deformation this basin is an example of a type of passive margins that cannot be considered solely as inert sites of sedimentation and of progressive subsidence and that are reactivated in a compressive pattern other examples include the kwanza basin angola and the brazil margin we investigated by means of 2 d thermomechanical modeling the structural and rheological heterogeneities that can lead to concentration of strain in this marginal basin we deduced that the deformation of the basin is due to its particular geometric features narrow and with a thick surrounding continental crust related to its position at the southern termination of the alps this sharp transition in terms of both geometry and rheological contrast is a main factor in explaining the weakness of the margin we discuss the importance of buoyancy forces versus tectonic forces as well as thermal effects on the observed reactivation influence of contrast in rheology between an oceanic type crust and continental crust is also studied geodynamical implications are proposed for the region the good agreement between the predicted localized deformation and the observed seismicity distribution should help improve seismic hazard assessment in the region

the geophysical exploration of the upper crust from the ligurian coast to the northern margin of the po valley problems and results abstract the available geophysical data are assembled and compared along an average profile that runs northwards from the ligurian coast near genoa crossing the apennines and the po basin and reaching the region of the lombardian lakes the main objective of this survey is a contribution to the knowledge of the structure of the upper crust in the transitional area from the ligurian to the padanian adriatic crust and its relationship both with the shallow geological features and with the lower crust gravity and aeromagnetic anomalies along several s n profiles are compared with the results of seismic surveys the latter are of variable type and reliability while the po basin has been intensively explored by a dense network of commercial near vertical profiles nvr only some wide angle lines war are available across the apennines the constraints of both seismic techniques are described as well as the difficulties of comparing the different sets of data gathered in various geological settings difficulties involved in geophysical exploration under a thick chaotic overburden like the one found in the apenninic range are also stressed the integrated profile supports the evidence of a sharp discontinuity both in the upper and in the lower crust between the ligurian and the adriatic domains

seismicity and crustal structure beneath the western ligurian sea derived from local earthquake tomography abstract in this paper we present and comment on the results of a tomographic inversion of p arrival times of local earthquakes to better understand the structure and features of the ligurian sea an oceanic basin originated in the oligocene miocene this tomographic inversion is the last step in a long and careful revision of the data available for the ligurian sea an accurate catalogue derived from a controlled compilation of data from the numerous stations monitoring seismic activity in this young oceanic basin has been used for computation of a one dimensional 1d reference model a high quality subset of the new catalogue has been used for the non linear 3d tomographic inversion by iteratively solving the coupled hypocenter velocity problem in a least square sense careful analysis of the resolution capability of the used data set has revealed the better resolved features for interpretation the resulting 3d model shows a high velocity layer extending from the northeastern side of the model where it lays about 30 km deep to the southwestern part where it shallows to 15 km the shallow part of this high velocity body is located near the original area of the opening of the ligurian sea that took place between the oligocene and early miocene its velocity is comparable with that of an oceanic moho around 7 8 km s a lens shaped high velocity body about 25 km long located at a depth of 8 15 km is interpreted as a series of ophiolitic bodies intruded into the upper crust

the gross structure of the crust under corsica and sardinia as part of the european geotraverse project egt a number of international cooperative seismic refraction surveys were carried out along the n s segment from the ligurian sea across the islands of corsica and sardinia to the sardinian channel between sardinia and north africa from 1982 to 1985 for all the experiments offshore explosions served as energy sources ranging from 200 to 1125 kg the main result is that the crust in the ligurian sea is of transitional type with a thickness of only 18 km the two continental blocks of corsica and sardinia have a maximum crustal thickness of 33 and 34 km with average crustal velocities of 6 4 and 6 3 km s respectively other results are that the internal crustal structure as derived from the available data in both islands is rather undifferentiated with only local evidence for a more steplike interface in the lower crust corsica 6 3 to 6 6 km s sardinia 6 5 to 6 8 km s there are also indications of a slight velocity inversion under the southwestern part of sardinia farther south in the sardinian channel the crustal thickness decreases again to 20 km a significant feature is the observed pn velocity this parameter increases from the relatively low value of 7 5 km s in the north ligurian sea to 7 7 km s and 7 9 km s for corsica and sardinia and finally to 8 0 km s under the sardinian channel these values reflect the tectonic evolution of that part of the mediterranean sea

a cross section of the lithosphere along the european geotraverse southern segment from the alps to tunisia abstract the european geotraverse southern segment egt s is a 200 300 km wide strip from the alps to tunisia which crosses the youngest tectonic provinces of europe where continued alpine compression is accompanied by recent extension e g in the ligurian sea and sicily channel the geophysical research along the egt s has been nearly continuous both on land and sea from 1982 to 1987 with deep seismic sounding dss experiments and collection of heat flow gravity magnetic seismological and seismotectonic data the new dss and seismic reflection data testify to the asymmetry of the alpine edifice the deepest part of the crust mantle boundary is found beneath the internal and external crystalline massifs where the european moho disappears after a steep flexure in the seismic reflection data the continuation of the moho discontinuity into the southern alpine domain is however evident in the seismic refraction data seismic evidence and heat flow data indicate incipient rifting in the ligurian sea which is underlain by a mantle with an anomalously low pn velocity of only 7 5 km s the palaeozoic crust of the sardinia corsica block exhibits a bowl shape with a rather undifferentiated internal structure average p wave velocity of 6 3 6 4 km s crustal thickness increases from 20 km at its margins to more than 30 km beneath the centre of the islands a thinned crust with thrusted blocks in its upper part characterizes the sardinia channel finally the preliminary dss results from tunisia show an abrupt deepening of the moho from 20 to approximately 35 km in the tell area very low average crustal velocity which requires a velocity inversion within the lower crust and subcrustal reflectors revealing a structured upper mantle

dynamics and seismotectonics of the west alpine arc abstract in this paper we present a comparative review of structural seismic and focal mechanism data from the west alpine arc in the western alps seismic activity is concentrated along an external belt corresponding to the penninic front and an internal belt corresponding to the austro alpine front and its southern extension these seismic belts are connected in the ne by a seismic lineament corresponding to the simplon and centovalli line and in the south by the e w trending seismic stura couloir located between the argentera and dora maira massifs the simplondashcentovalli tonale system and the stura couloir are dextral and sinistral strike slip systems respectively this implies a westward translation of the west alpine arc and the po plain based on these observations a seismotectonic model is proposed in which the frontal penninic thrust and the basal surface of the accretionary wedge corresponding to the penninic sole thrust are reactivated activity along the frontal thrust increases the arcuate shape of the western alps and disengages them from the central and the ligurian alps along the tear faults of the simplondashcentovalli tonale system and the stura couloir respectively in the wider framework of northern italy the sector of the eastern alps north of the gailtal line is moving in an orogendashparallel direction towards the east areas with lateral escape in opposite directions towards the west for the po plain and towards the east for the eastern alps north of the gailtal line are separated by the south alpine atesine indenter a model postulating a double lateral escape and a central indenter matches most of the features of the models of poinconnement the seismic features of northern italy agree with the seismicity of the stable sector of northern europe up to the north sea this area is fragmented into blocks bounded by seismic bands some of which probably reactivate pre existing structures the overall stress field of cratonic europe is dominated by ndashnw directed trajectories of maximum horizontal compression the seismicity of the european alpine foreland is interpreted as the response of a stable block to the same stress field of northern italy which is induced by the ondashgoing nw se africa europe convergence we suggest that the westward translation of the west alpine arc continues at present and is the driving mechanism of the observed seismicity

an introduction to the european geotraverse project first results and present plans abstract the european geotraverse egt is an international multidisciplinary project focused on a north south orientated lithospheric profile 4000 km long and of varying width extending from northernmost scandinavia to north africa this profile consists of three interlinking segments northern central and southern comprising a continuous succession of tectonic provinces ranging from the oldest precambrian areas of the baltic shield to the currently active area of the western mediterranean the broad aim of the egt project is to obtain a better three dimensional picture of the structure state and composition of the continental lithosphere to use as a basis for an understanding of its evolution and dynamics all of the 12 major projects that constitute the egt joint programme have now been initiated and several of these projects are nearing completion along the northern segment data from the fennoscandian long range project fennolora a 2000 km long seismic profile across the precambrian baltic shield show that except beneath southern sweden the shield is characterized by a high velocity 40 50 km thick crust including a 5 10 km thick crust mantle transition zone an alternating series of 4 6 high and low velocity zones is present in the subcrustal lithosphere the base of which increases in depth from ca 110 km to ca 230 km from south to north beneath the shield the top of the mantle transition zone lies at a depth of about 450 km the second major project along this segment the eugeno s european geotraverse northern segment southern part project is a multidisciplinary study of the fennoscandian border zone and was largely completed in 1984 with the realization of a large scale seismic experiment preliminary interpretation of the excellent data obtained indicate the presence of strong lateral variations in internal crustal structure beneath the danish basin field work for a third major project a multidisciplinary transect of the archaean and early proterozoic terrains in the northernmost part of the shield the polar profile was carried out in 1985 a series of deep seismic reflection lines has so far been realized in the area of the central segment in the context of german national programmes first interpretations of the seismic data from a 260 km long profile across the two main intra variscan hercynian lineaments have shown the presence of numerous horizons making up a highly reflective zone in the lowermost 10 km of the crustal section studied and distinct changes in reflectivity between the main variscan tectonic zones in 1986 the entire segment will be investigated in detail in an ambitious international programme of integrated geological and geophysical studies a series of seismic experiments termed egt s have been carried out across the southern segment in 1982 1983 and 1985 interpretation of data from the 1982 and 1983 experiments have led to several interesting results including 1 1 the suggestion that two crust mantle like interfaces exist beneath the po basin at depths of about 35 and 50 km and adjacent tectonic units these interfaces marking a deep contact zone between the adriatic and european plates 2 2 in the area between genoa and corsica the ligurian sea is underlain by a greatly thinned distinctly layered section of continental crust and 3 3 corsica and sardinia are underlain by bowl shaped typically variscan continental crusts the 1985 phase of seismic surveys focused on crustal structure beneath tunisia and the adjacent seas in addition two off traverse projects are being realized first a wide aperture network of autonomously recording seismic stations nars installed along the line gothenburg malaga between 1982 and 1984 is already yielding high quality data on the upper 600 700 km of the mantle second an investigation of lithospheric seismic anisotropy in the area of the iberian peninsula is being organized for 1987 1988 finally of great importance are the systematic compilation of existing data and where needed in critical regions collection of new geophysical and geological data presently being carried out for the entire area encompassed by the egt it is expected that these compilations will be completed by 1987 at about the same time that full results from the main large scale seismic experiments become available enabling the construction of an integrated lithospheric cross section along the egt requiring a final phase of intensive multidisciplinary collaboration

crustal features of some main suture zones along the european geotraverse the european geotraverse egt crosses along a 4000 km profile from the north cape to tunisia the following main suture zones the tornquist teisseyre zone between the baltic shield and the variscan realm the transition zones between rhenohercynian and saxothuringian as well as between saxothuringian and moldanubian zones in the variscan part of central europe and the collision zone between the european continent and the adriatic microplate

several location methods for underwater shots in the gulf of genoa western mediterranean structural implications abstract during the egt survey 50 underwater shots were detonated on a n s section through the gulf of genoa running from the northern margin 44 12 n towards corsica 42 90 n along the 9 e meridian the aim of this work is in a first stage to establish the propagation model of regional phases in this region and consequently to improve the location of epicentres and afterwards to refine our structural knowledge of this complex crustal area the relocation of these shots was carried out with arrival times of seismic signals recorded at land stations we have used different location methods all of which led to similar crustal models they reveal a low p n velocity area in the northern ligurian sea and in the gulf of genoa with a 20 km thick crust in the southern part approximately south of latitude 43 7n a 4 km thick oceanic crust covered by 8 km of sediments is clearly confirmed using these models a significant improvement of epicentre locations was obtained these improvements to propagation models lead to the two main structural conclusions 1 1 in the southern part of the investigated area the spread of an oceanic type domain as far as the foot of the continental margin 2 2 a sharp transition between the two domains of different stretching rate the northern one with a moho depth of about 20 km and the southern one with an average moho depth of about 14 km these observations substantiate the presence of a transform margin between the rifted gulf of genoa and the oceanic type ligurian basin

european geotraverse a seismic refraction profile across the ligurian sea abstract a seismic refraction profile was shot in the ligurian sea between italy and corsica in september 1983 the profile which is part of the southern portion of the european geotraverse was shot using small dynamite charges and the seismograms were recorded by ocean bottom seismometers and land stations resulting in a number of partially overlapping reversed profiles the refraction data were interpreted by means of the velocity intercept and ray tracing methods using seismic reflection derived velocity depth information for the sedimentary section refraction velocities of 4 8 6 0 and 6 6 km s 1 were calculated for the base of the sedimentary section crystalline basement and lower crust respectively an upper mantle velocity of 7 4 km s 1 was inferred using the refraction profiles recorded on corsica the interpretation of the data indicates a prominent high in the crystalline basement in the northern part of the profile while the sedimentary section increases in thickness from about 1 5 km over the basement high to over 6 km between the basement high and corsica and includes a considerable thickness of pre miocene sediments the crust mantle boundary shows shoaling towards the centre of the profile where a minimum crustal thickness of 16 km is reached the model therefore is that of a stretched and thinned continental crust which was rifted in oligo miocene times the presence of a low velocity upper mantle may be indicative of the present renewal of subcrustal activity under the ligurian sea

crustal structure from the ligurian sea to the northern apennines a wide angle seismic transect abstract a new wide angle seismic reflection profile 250 km long was shot along a line extending from parma in the apennines to the deepest part of the ligurian sea thirty seismic land stations lobs and 25 ocean bottom seismographs obs recorded 54 shots fired at sea the resulting 55 record sections allowed the definition of the transition from continental to oceanic crust in a geologically complex and hitherto poorly understood region the subducted continental crust beneath the northern apennines has a thickness of 40 km consisting of 30 km of igneous crust overlain by 10 km of sediments two sedimentary layers are identified with vp velocities in the range from 2 8 to 5 5 km s the igneous portion of continental crust thins gradually to approx 11 km across a 120 km wide zone extending from the southwestern part of the apennines some 20 km inland into the ligurian sea an easterly thinning low velocity body 7 2 7 5 km s immediately beneath the base of the crust is interpreted as an underplated unit emplaced prior to the onset of seafloor spreading this may have been initiated by magmatic activity along the incipient continental oceanic boundary a basement high coincides with the northeastern edge of the ligurian sea and is interpreted as part of the alpine ophiolite belt indicating strike slip motion the two sedimentary layers above the transition zone are typically 5 km thick and have slightly lower velocities than those further to the northeast a sharp continent ocean break is recognised in the ligurian sea oceanic crust is 6 7 km thick and is overlain by a two layered sedimentary succession approx 5 km thick mantle velocities in the region range from 7 9 km s beneath the thinned crust to 8 1 km s beneath the thick crust the ratio c o of continental to oceanic crustal thickness at the continent ocean transition is approx 1 5 and the overall crust stretching factor at that boundary is approx 3 5 these values are similar to other continent ocean boundaries and indicate that the oceanic crust in the ligurian sea formed largely by stretching with a small pull apart component

shear controlled evolution of the red sea pull apart model abstract results of seismic and other geophysical investigations suggest that strike slip processes controlled the break up of the arabian plate from africa and initiated the red sea rift early oceanisation was facilitated by nucleation of pull apart basins and massive intrusives the evolution of the red sea has gone through different stages it was a zone of structural weakness already during the pan african orogeny approximately 600 ma a major reactivation however that gradually led to the present day configuration was initiated during the late oligocene with intense magmatic activity and the development of a continental rift wrench faulting played a key role in the early evolution of the red sea as it shaped most of its western flank as a sharp plate boundary and resulted in the generation and rapid oceanisation of linearly arranged pull apart basins spatial distribution of these basins reflects the geometry of the strike slip zone which was controlled by pre existing fault systems like the najd shear system the central african fault zone or the onib hamisana and baraka suture zones strike slip motion along the latter zones of weakness influenced mainly the egyptian and sudanese coastal areas arabia was therefore separated from africa by oceanisation in those regions where pull apart basins developed they were still connected in the in between segments by stretched continental crust with arabia as the moving and africa as the stable plate the eastern red sea flank was formed by pure shear through stretching thinning and diffuse extension as a consequence the eastern and western flanks of the red sea are asymmetrical the acceleration of the movement of arabia in early middle miocene could no longer be accommodated by the opening in the gulf of suez and consequently the dead sea strike slip fault developed approximately 14 ma ago since plate motion was still oblique to the major structural trends the pull apart evolution on the western flank continued and the oceanisation was accentuated while in the north the eastern flank developed en echelon fractures of aqaba orientation seafloor spreading commenced 5 ma ago at parts of the central and southern red sea this final stage is also responsible for the bathymetry with maximum depth values of 3000 m in the seafloor spread areas and a much shallower basin in the north the metalliferous red sea deeps are either associated with this infant mid ocean ridge or with the en echelon fractures in the north

a possible mechanism for the thermal asymmetry of the ligurian basin we propose a thermo mechanical model and a new interpretation of heat flux data for the ligurian basin that may be a key to understanding the evolution of the nw mediterranean the model incorporates the removal of a portion of mantle lithosphere to explain the heat flux and subsidence anomaly of the eastern corsican margin of the basin this process is envisaged as a result of eastward asthenosphere flow induced by the apennines subduction system after a heating phase time dependent conductive cooling and re thickening of the lithosphere result in re equilibrium of the thermal gradient to its initial value such a rifting mode can account for the asymmetric heat flux and subsidence pattern observed across the basin and the present day lithospheric thickness