source parameters of the 1992 melilla spain mw 4 8 1994 alhoceima morocco mw 5 8 and 1994 mascara algeria mw 5 7 earthquakes and seismotectonic implications source mechanisms of the melilla alhoceima and mascara earthquakes including fault plane solutions waveform modeling and spectral analysis are presented strike slip solutions have been obtained for the melilla and alhoceima earthquakes and reverse faulting for mascara teleseismic p wave inversion using broadband data show a complex mechanism for the alhoceima earthquake formed by two subevents at very shallow depth 7 and 8 km and scalar seismic moments of 1 1 10e 17 n m and 4 8 10e 17 n m the mascara earthquake was a single event with a shallow depth 4 5 km and a scalar seismic moment of 3 3 10e 17 n m results of the alhoceima melilla and mascara earthquakes together with 53 focal mechanisms in the region show a regional stress regime that corresponds to horizontal compression in a nw se direction associated with the convergence between eurasia and africa a change of the stress regime in the plate boundary of the ibero maghrebian region has been found

an integrated geophysical investigation of recent seismicity in the al hoceima region of north morocco abstract data produced by the moroccan national seismological network and marine seismic reflection profiles are used to investigate the most seismically active region in morocco located on the mediterranean coast at the intersection of the rif mountain belt and the submarine alboran ridge this region in the vicinity of the city of al hoceima marks an east west transition in the marine and land deformation styles of the distributed plate boundary between africa and iberia and was the site of an m w 6 0 earthquake on 26 may 1994 the epicenter of the al hoceima earthquake is relocated onshore refining the initial submarine location close to the alboran ridge the spatial distribution of foreshocks and aftershocks shows a ne sw trend that continues partly offshore and is subparallel to the earlier yet still prominent miocene geologic structural trend the predominantly strike slip focal mechanism for the al hoceima event is characteristic of earthquakes in the region marine seismic reflection profiles that intersect the offshore region of seismicity image active high angle faults with possible strike slip components the seismicity trend is not directly related to the submarine alboran ridge or the geomorphologically prominent nekor fault deformation appears to be occurring on a number of subsidiary strike slip faults that together compose a ne sw zone of distributed shear the distributed strike slip and documented normal faulting taking place in the eastern rif mountains although characteristic of the rif region are in contrast to the thrusting style of deformation that occurs farther to the east in the algerian tell atlas this may be related to the reported lateral variations and evolution of the convergent plate boundary in these regions during the neogene and quaternary times

moment tensor solutions for small and moderate earthquakes in the ibero maghreb region 1 we applied time domain moment tensor inversion of local and regional waveforms to small and moderate mw 3 5 5 7 shallow earthquakes from the iberian peninsula northern morocco and northern algeria for the 6 years period from november 1995 to march 2002 and the previous network of autonomously recording seismograms nars experiment moment tensor solutions were obtained for 58 events considerably increasing the total number of available solutions in the study area for each event we performed a moment tensor inversion and a double couple grid search for simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation the computed mechanisms show regional consistency a large part of the iberian peninsula is characterized by normal faulting mechanisms with sw ne oriented t axes thrusting and se nw compression is dominant in algeria in the alboran sea the westernmost part of the mediterranean and the transition between both regimes strike slip mechanisms dominate with approximately n s oriented p axes this pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations

models of the complex source of the el asnam earthquake abstract the el asnam earthquake of 10 october 1980 was originated by a thrust across a sw ne oriented fault 36 km long and 15 km wide it is a complex event with a rupture propagating from the sw to the ne fault mapping hypocenter distribution and b factor studies indicate fault branching to the ne a dislocation model is used to explain the branch with normal faulting at beni rached as a consequence of the thrust across a main fault that changes orientation the mechanism of the 1954 earthquake must be similar even though only normal faulting was observed at the surface

intermediate and deep earthquakes in spain recent improvements in the seismological networks on the ibero maghrebian region have permitted estimation of hypocentral location and focal mechanisms for earthquakes which occurred at south spain alboran sea and northern morocco of deep and intermediate depth with magnitudes between 3 5 and 4 5 intermediate depth shocks range from 60 to 100 km with greater concentration located between granada and malaga fault plane solutions of 5 intermediate shocks have been determined they present a vertical plane in ne sw or e w direction seismic moments of about 1015 nm and dimensions of about 1 km have been determined from digital records of spanish stations p wave forms are complex this may be explained by the crustal structure near the station discontinuities in the upper mantle and inhomogeneities near the source deep activity at about 650 km has only 3 shocks since 1954 1954 1973 1990 shocks are located at a very small region fault plane solutions show a consistent direction of the pressure axis dipping 45 in e direction for the 1990 shock seismic moment is 1016 nm and dimensions 2 6 km thep waves are of simpler form with a single pulse the intermediate and deep activities are not connected and no activity has been detected between 100 and 650 km the intermediate shocks may be explained in terms of a recent subduction from africa under iberia in se direction the very deep activity must be related to a sunk detached block of lithospheric material still sufficiently cold and rigid to generate earthquakes

estimating bulk rheological properties of flowing snow avalanches from field data reference lhe article 2004 002view record in web of science record created on 2007 09 04 modified on 2016 08 08

inferences on flow mechanisms from snow avalanche deposits the deposit structure of 20 very small to large avalanches that occurred in the davos area eastern swiss alps during winters 2004 05 and 2005 06 was investigated snow cover entrainment was significant in the majority of events and likely to have occurred in all cases evidence was found both for plough like frontal entrainment especially in wet snow avalanches and more gradual erosion along the base of dry snow avalanches several of the dry snow avalanches both small and large showed a fairly abrupt decrease in deposit thickness in the distal direction often accompanied by changes in the granulometry and the deposit density combined with other observations snow plastered onto tree trunks deposit less flow marks in bends etc and measurements at instrumented test sites this phenomenon is best explained as being due to a fluidized low density flow regime that formed mostly in the head of some dry snow avalanches the mass fraction of the fluidized deposits ranged from less than 1 to 25 of the total deposit mass fluidization appears to depend rather sensitively on snow conditions and path properties

interface inversion using broadside seismic refraction data and three dimensional travel time calculations a procedure has been developed to interpret densely sampled broadside seismic refraction data recorded from a large air gun array first arrival travel times are inverted to find the structure on an interface beneath the shot line travel times are calculated for three dimensional velocity models using a rapid finite difference algorithm adapted to allow variable sampling of the model and the determination of rays a simple inversion parameterization eliminates the need for matrix inversion the complete inversion procedure is computationally rapid yet allows the determination of detailed three dimensional structure broadside refraction data recorded in the queen charlotte basin offshore western canada during a multichannel reflection experiment are used to demonstrate the procedure the data are inverted for the basement interface beneath the shot line defining a rapidly varying thickness of sedimentary basin fill the results of the inversion stimulate a reinterpretation of the reflection data and identify a new major basement fault structure out of the plane of the reflection section is determined including the strike of the fault and other nearby features

power laws and snow avalanches 1 this paper presents evidence of frequency size power laws in several groups of snow avalanche paths other natural hazards such as earthquakes and forest fires exhibit similar power law relationships in addition an analysis of the response of one group of snow avalanche paths to storms through time demonstrates a power law between the response of the system and the binned frequency of those responses our results as well as our experience with these complex non linear systems are consistent with self organized criticality the practical implication of this work is that the frequency size relationship for small and medium sized avalanches may be useful for quantifying the risk of large snow avalanches within a group of avalanche paths

the savage hutter avalanche model how far can it be pushed the savage hutter sh avalanche model is a depth averaged dynamical model of a fluid like continuum implementing the following simplifying assumptions i density preserving ii shallowness of the avalanche piles and small topographic curvatures iii coulomb type sliding with bed friction angle delta and iv mohr coulomb behaviour in the interior with internal angle of friction phi or delta and an ad hoc assumption reducing the number of mohr s circles in three dimensional stress states to one we scrutinize the available literature on information regarding these assumptions and thus delineate the ranges of validity of the proposed model equations the discussion is limited to relatively large snow avalanches with negligible powder snow component and laboratory sand avalanches starting on steep slopes the conclusion of the analysis is that the sh model is a valid model for sand avalanches but its mohr coulomb sliding law may have to be complemented for snow avalanches by a second velocity dependent contribution for very small snow avalanches and for laboratory avalanches starting on moderately steep and bumpy slopes it may not be adequate

snow avalanche mass balance calculation and simulation model verification two or three dimensional avalanche simulation models offer a wide range of applications however a challenging model verification process is demanded accompanied by a reliable determination of model input parameters we show that a verification process can be arranged with remote monitoring data from an artificially triggered avalanche leading to the calculation of avalanche mass balance two numerical methods are applied to increase the quality of the parameter fit and to reduce the number of simulations the quality of the parameter fit is verified by comparing measured and simulated run out lengths in addition a cross check is performed using velocities derived from doppler radar measurements

neogene extensional collapse in the western mediterranean betic rif alpine orogenic belt implications for the genesis of the gilbraltar arc and magmatic activity the betic rif orogenic belt crops out in the western mediterranean and constitutes the westernmost part of the alpine edifice the building up of this belt by compressional nappe tectonics occured during a series of alpine deformational episodes subsequent neogene extension resulted from the collapse of the previous compressional edifice through major extensional detachment systems this episode was accompanied by cafe alkaline to shoshonitic and lamproitic volcanism tectonic denudation of metamorphic core complexes and emplacement of peridotite bodies as a final consequence of the evolution of detachment systems furthermore we relate the generation of the gibraltar arc and the opening of the alboran sea to this major extensional event finally two main stages of tectonic denudation of these detachment systems are defined 1 nevado filabride stage with ex humation of metamorphic core complexes and 2 ronda beni boussera stage with a more advanced degree of denudation leading to the exhumation of upper mantle peridotites which may be tentatively termed mantle core complexes

variation of deposition depth with slope angle in snow avalanches measurements from vallee de la sionne 1 the snow surface height was precisely measured with a laser scanner before and after the passage of two dry mixed avalanches in vallee de la sionne during the winter of 2005 2006 the measurements were used to calculate the depth of the deposited snow along each entire avalanche path with a height resolution of 100 mm and a horizontal resolution of 500 mm these data are much more accurate than any previous measurements from large avalanches and show that the deposit depth is strongly negatively correlated with the slope angle that is on steep slopes the deposit is shallow and on gentle slopes the deposit is deep the time evolution of the snow depth showing the initial erosion and final deposition as the avalanche passed was also observed at one position using a frequency modulated continuous wave radar measurements at a nearby position gave flow speed profiles and showed that the avalanche tail consists of a steady state subcritical flow that lasts for about 100 s eventually the tail slowly decelerates as the depth slightly decreases and then it comes to rest we show that the dependency between the slope angle and the deposition depth can be explained by both a cohesive friction model and the pouliquen h stop model

stress and palaeostress in the betic rif cordilleras miocene to the present palaeostress orientation in the betic rif cordilleras can be determined for the miocene to the quaternary by analysis of brittle microstructures faults joints striated pebbles and stylolites in the central and northern south iberian domain 1 was subhorizontal and trended nw se from the early miocene to the present in the northern alboran domain from the burdigalian to the serravallian palaeostress ellipsoids were oblate with 3 subhorizontal and trending ene wsw in the southern part of the south iberian domain and in the northern part of the alboran domain betic cordillera from the tortonian to the quaternary palaeostress ellipsoids were variable in the granada region they were prolate with 1 subvertical but in the almeria region they were triaxial with 2 subvertical and 3 subhorizontal and trending ne sw to e w in the rif the alboran and african maghrebian domains were affected by palaeostresses with 1 subhorizontal varying from ne sw in tortonian times to n s in the plio quaternary a study of earthquake focal mechanisms by the right dihedra method indicates that the present day general stress field around the betic rif cordilleras is compressional with 1 subhorizontal and trending nw se in the betic rif cordilleras this general stress field is modified and the present day orientations of 1 2 and 3 are nearly the same as those of the palaeostresses in the pliocene and quaternary the distribution and evolution of stresses in the betic rif cordilleras from the miocene to the present can be correlated with the main neogene deformations extensional structures in the central and northern alboran domain and the southern part of the south iberian domain and compressional structures in the south iberian and african maghrebian domains and in the southern part of the alboran domain

monitoring of snow avalanches using a seismic array location speed estimation and relationships to meteorological variables 1 monitoring snow avalanches is necessary in order to better understand their triggering mechanisms and ultimately improve forecast performance seismic monitoring has been developed by several groups over the last 20 years and holds great potential to detect locate and characterize snow avalanches during the 2009 2010 winter a seismic antenna was installed in the french alps close to the village of saint christophe en oisans 1700 m above sea level the array of seven sensors operated during 50 days in october and november 2009 under snow free conditions and during 40 days in january and february 2010 in presence of snow it recorded different types of seismic events including snow avalanches rockfalls shots and regional and local microearthquakes eighty avalanche signals were visually identified using a beam forming method we were able to locate snow avalanches on slopes of various orientations in a radius of about 3 km and track their propagation the location technique allowed for the estimation of avalanches front speed which ranged between 12 and 32 m s 1 the method can also distinguish dry and wet snow avalanches durations of avalanches can be as long as 380 s because of the length of the slopes in the area seismic monitoring provides a catalog of avalanches with precise times which can be used to analyze the impact of meteorological forcings on the avalanche triggering snowfall is found to be the dominant forcing of avalanche activity during this period as revealed by the strongest correlation for the period of study our results suggest that the impact of precipitation on the snowpack instability lasts for about 6 days

the el asnam algeria earthquake of 10 october 1980 multiple source mechanism determined from long period records we present a study of the el asnam algeria earthquake of 10 october 1980 from a large collection of long period surface and body wave records the focal mechanism of the main shock is well constrained by the p wave first motions at teleseismic distances and field observations it was a thrust event on a plane striking n45 e and a dip angle of 54 to the north it had a small component of left lateral motion 83 ouyed et al 1981 gaudemer et al 1981 this earthquake was very well recorded on wwssn stations and on gdsn and ida digital stations with a good azimuthal distribution from these records we confirm the focal solution and obtain a seismic moment m o 5 1026 dyne cm the p wave seismograms indicate a complex source we show that it is not sufficient to model the source by a multiple event but it is also necessary to include a propagation effect in order to explain accurately the waveform with assumptions based on field observation of the surface breaks we model the p waves including two discontinuities of the propagation along the fault plane and obtain a good agreement of the waveform

ground motion hazard values for northern algeria this study examines distinctive features of ground motion parameters in northern algeria an initial computation of seismic hazard in terms of horizontal peak ground acceleration pga and spectral acceleration sa at different periods damped at 5 is carried out for three different types of soils rock stiff soils and soft soils for return periods of 100 and 475 years in addition uniform hazard spectra uhs are computed for these two return periods at several locations in the region then the uhs computed for different soil types are proposed as a starting point to define elastic design spectra for building code purposes we have used the well known newmark hall approach as proposed in the most recent international building codes the sa 0 2 s value is used to establish the spectral region for lower periods region controlled by acceleration whereas the sa 1 0 s value is used to establish the spectral region for intermediate periods region controlled by velocity we also obtained important relations dependent on site condition between sa 0 2 s sa 1 0 s or samax values and the pga for both return periods of 100 and 475 years other relationships between pga or samax values have also been derived for return periods of 100 and 475 years in this case independent of site condition

postseismic deformation at el asnam algeria in the seismotectonic context of northwestern algeria summary we use a combination of seismicity tectonic features focal mechanisms seismic strain and postseismic movement to study the western part of north algeria the el asnam region and its surrounding area in particular a seismotectonic map of this part of algeria delimited by the mediterranean sea in the north and the tellian mountains in the south was built from available geological and seismological data an examination of this map shows that the most significant earthquakes are concentrated along tectonic features and quaternary basins elongated in an east west direction suggesting nnw sse compressional movements during the large el asnam earthquake of 1980 october 10 m 7 1 vertical movement was measured along a 40 km northeastsouthwest thrust fault these movements were determined geodetically in 198 1 with reference to a basic network previously measured in 1976 in order to control postseismic movement and to ensure the monitoring of the seismic area a dense geodetic network has been regularly measured since 1986 both in planemetry and altimetry the results of the altimetric remeasurements show significant vertical movements the elevation changes of the benchmarks have been deduced from precise levelling measurements a remarkable uplift 5 1 5 1 9 mm yr of the northwestern block during the 1986 91 period has been observed whereas the southeastern block is seen to be relatively stable the sar el maiirouf anticline situated along the central segment of the el asnam surface breaks appears to be growing with a maximum postseismic slip rate of 9 6 1 4 mm yr i the mean uplift rates computed for the northwestern block support the view that the 1954 earthquake did not occur on the same reverse fault as the 1980 event

the 1954 and 1980 algerian earthquakes implications for the characteristic displacement model of fault behavior joint epicenter determination of earthquakes that occurred in northern algeria near ech cheliff named orleansville in 1954 and el asnam in 1980 shows that the earthquake of 9 september 1954 m 6 5 occurred at nearly the same location as the earthquake of 10 october 1980 m 7 3 the 1954 main shock and earliest aftershocks were concentrated close to the boundaries of segment b nomenclature of deschamps et al 1982 king and yielding 1984 of the 1980 fault system which was to experience approximately 8 m of slip in the 1980 earthquake later aftershocks of the 1954 earthquake were spread over a broad area notably in a region north of the 1980 fault system that also experienced many aftershocks to the 1980 earthquake the closeness of the 1954 main shock and earliest aftershocks to the 1980 segment b implies that the 1954 earthquake involved either 1 rupture of segment b proper or 2 rupture of a distinct fault in the hanging wall or footwall block of segment b the first interpretation cannot be accommodated in the characteristic displacement model of fault behavior but instead requires a model such as the time predictable model which would permit slip in 1954 to have released only a fraction of the elastic strain that was stored on segment b and which would later be released in 1980 the second interpretation specifically with rupture in the hanging wall block of segment b accounts more directly than the first interpretation for differences in the focal mechanisms and ground deformations associated with the two main shocks this interpretation is therefore preferred the second interpretation is consistent with a characteristic displacement model of the 1980 fault system no matter how it is modeled the algerian episode provides an example of an earthquake 1954 that was large enough to perhaps be judged the culminating event of the seismic cycle in a regionally important fault zone but that was followed instead by an even larger shock 1980 the space time characteristics of the episode are unusual enough that they cannot represent the most likely mode of strain release on reverse fault systems in general but the episode should be viewed as one possible scenario for the evolution of seismicity on other such fault systems

seismic hazard in northern algeria using spatially smoothed seismicity results for peak ground acceleration seismic hazard in terms of peak ground acceleration pga has been evaluated in northern algeria using spatially smoothed seismicity data we present here a preliminary seismic zoning in northern algeria as derived from the obtained results initially we have compiled an earthquake catalog of the region taking data from several agencies afterwards we have delimited seismic areas where the b and mmax parameters are different finally by applying the methodology proposed by frankel seismol res lett 66 1995 8 and using four complete and poissonian seismicity models we are able to compute the seismic hazard maps in terms of pga with 39 3 and 10 probability of exceedance in 50 years a significant result of this work is the observation of mean pgavalues of the order of 0 20 and 0 45 g for return periods of 100 and 475 years respectively in the central area of the tell atlas d 2003 elsevier b v all rights reserved

possible erosion mechanisms in snow avalanches snow erosion and entrainment processes in avalanches are classified according to their mechanisms the flow regimes in which they occur and their spatial position within the avalanche simple but process specific models are proposed for erosion by impacts abrasion plowing and blasting on the basis of order of magnitude estimates the first three mechanisms are clearly expected to be important the fourth mechanism stipulates that the compaction of the snowcover ahead of the avalanche leads to the flow of escaping air just in front of the avalanche that may disrupt the snowcover and support formation of a saltation layer the effects of this hypothetical mechanism resemble those of the plowing mechanism all mechanisms depend strongly on the snow properties but with plausible parameter values erosion rates at or above the experimentally found rates are obtained the entrainment rate of an avalanche is most often limited by the shear stress needed to accelerate the eroded snow to avalanche speed

study of a large scale dry slab avalanche and the extent of damage to a cedar forest in the makunosawa valley myoko japan accurate measurements of snow avalanche flows in forests are rare to understand how forests can stop avalanches we study a mixed flowing avalanche that stopped in a cedar cryptomeria japonica forest in japan the large scale dry slab avalanche occurred in the makunosawa valley in myoko on 17 february 2008 and damaged many trees the site contains a geophone and other devices to detect avalanche activity a nearby meteorological station provides weather information post event observations were made of the scale of the avalanche and tree damage these showed that the avalanche released from the east southeast facing slope at 1700 m a s l snow debris reached 770 m a s l the horizontal runout distance was 3000 m the area of the runout zone was 10 ha and the snow water equivalent of debris was 400 1500 mm the mass of the avalanche was roughly estimated at 5 10 10 7 kg 1 2 10 5 m 3 we used snowpack simulation models to estimate the height of the fracture zone the simulations revealed that a faceted snow layer formed at 2 m and the stability index was 0 5 poor at the time of the avalanche release due to heavy snowfall we estimated the avalanche velocity from the bending stress of the broken cedar trees in order to verify the effect of forests in reducing avalanche velocity the avalanche was estimated to flow into the forest at a velocity of 26 31 m s 1 with a 17 m high powder snow layer and a dense flow layer 2 m in height it appears to have slowed down and stopped at 130 m after penetrating the upper edge of the forest

discussion of origins of hinterland basins to the rif betic cordillera and carpathians abstract the hinterland basins of the rif betic cordillera western alboran sea and the carpathians pannonian basin are in part composed of a thick in excess of 3 4 km thermal sag basin sequence the underlying crust has been thinned to 25 km in parts of the pannonian basin and to 15 km in parts of the alboran sea modern tectonic models for these areas envision tectonic collision and thickening of the crust followed by crustal thinning either by gravitational collapse back arc extension or a combination of the two contemporaneous with thrusting basin and range type extension has been envisioned for parts of these extensional collapse systems extensional features are common and they interact in a complex way with strike slip systems flexural cantilever modelling agrees with earlier mckenzie type pure shear modelling of the extensional systems in suggesting that extension alone cannot generate sufficient thermal decay to explain the great thickness of the sag basins associated with the alboran sea and pannonian basin consequently it is suggested that uplift of the asthenosphere accompanying subduction roll back is an important factor in the evolution of these basins roll back of the mantle lithosphere permits hot asthenospheric mantle to upwell and lie close to the base of the crust initially uplift and erosion of the crust overlying the asthenosphere occurs as the thermal perturbation cools the crust thermally subsides to produce a large sag basin

a mass conserving fast algorithm to parameterize gravitational transport and deposition using digital elevation models 1 many natural phenomena such as snow avalanches debris flows or lahars involve gravitational transport and deposition that is largely governed by topography this paper describes a fast and mass conserving algorithm to parameterize mass transport and deposition mtd over a digital elevation model the algorithm is an extension to existing flow routing and terrain parameterization techniques its fast execution allows application over large areas or its incorporation into other models e g distributed glacier mass balance in mountain topography the proposed method does not include effects of kinetic energy and thus neglects potential uphill flow of fast moving mass the application of mtd is described at the example of small and frequent snow avalanches in steep terrain for which the required parameters are approximated from published data the algorithm mtd has been developed and is described for the gravitational redistribution of snow but it is also applicable to other types of mass movements

role of strike slip faults in the betic rifian orogeny abstract a new model for the betic rifian orogeny of the western mediterranean spain and north africa is proposed in which four strike slip faults play an important role the faults are not of the same age two faults the left lateral jebha fault to the south in morocco and principally in the mediterranean sea and the right lateral north betic fault southern spain to the north define the boundaries of the alboran block betic and rifian internal zones final movement along these faults was during the burdigalian time two other faults the left lateral nekor fault north africa to the south of the jebha fault and the right lateral crevillente fault somewhat to the north of the north betic fault define a larger alboran block including part of the betic and rifian external zones that was present during the tortonian the following sequence of events is proposed 1 a during the eocene and oligocene the african and european plates converged in a n s sense causing the breakup and overthrusting of the betic rifian and kabyle internal zones and then the movement towards the wsw of the alboran block by slip along the jebha and north betic faults 2 b by the end of burdigalian time movement along the jebha and north betic faults ceased 3 c with continued n s convergence the nekor and crevillente faults which bound a larger alboran block were formed during the mid and late miocene the arc of gibraltar the zone lying between the four major faults seems to be a result of wsw motion of a crustal block being thrust over external zones the model proposed adds to the earlier idea that tectogenesis proceeds from the interior to the exterior of an erogenic belt in the betic rifian orogeny major strike slip fracture zones shifted to the exterior of the orogenic belt as the orogeny progressed in order to relieve the stress caused by locking of the more internal faults

seismogenic zone survey by algerian telemetered seismological network case study of rouina earthquake 19 january 1992 abstract a new telemetered seismological network has been recently installed in northern algeria at present this new seismic network includes 30 stations with a final goal of 32 stations connected by radio and dedicated telephone lines to a centre located at the craag headquarters in alger bouzare ah the algerian telemetered seismological network atsn stations are all equipped with short period seismometers monitoring by this network will allow a more precise knowledge of the seismicity in algeria and southern europe as an example the sequence of the rouina earthquake m 5 2 of 19 january 1992 recorded by the atsn is described

seismotectonics of the ibero maghrebian region abstract a study of the seismotectonics of the ibero maghrebian region is presented as deduced from main geological features seismicity and focal mechanism data the hypocentral distribution of shallow intermediate depth and deep earthquakes is analyzed the direction of the stress distribution is inferred from the focal mechanism of 24 selected events a seismotectonic framework summarizing these results together with the main geological features shows that a nw se general direction of horizontal compressive stresses is present in the region with a localized zone of horizontal tensions in the betics and the alboran sea the presence of intermediate depth and deep earthquakes is tentatively explained as caused by two consecutive processes of subduction

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

field experiments and numerical modeling of mass entrainment in snow avalanches 1 snow entrainment alters the speed and hence the run out distance of avalanches yet little is known about this significant process we studied entrainment in snow avalanches using observations from 1 the swiss vallee de la sionne test site 2 the italian pizzac site 3 catastrophic avalanches that occurred during the winter 1998 1999 in switzerland and 4 a medium sized spontaneous avalanche that occurred in 2000 in davos switzerland we determined mass and energy balances for 18 avalanche events on average the mass increased by a factor of 4 the primary mode of entrainment appeared to be frontal ploughing although entrainment behind the avalanche front was also observed step entrainment where a snow cover layer fractures and is entirely consumed by the avalanche also occurred basal erosion was negligible mass availability and snow cover structure were the limiting factors governing entrainment other factors such as track topography and avalanche dimension played a secondary role using the experimental results we introduced an entrainment model into a saint venant type flow model where the internal shear deformation of the avalanche is governed by a bagnold law and the shear stress at the basal layer is treated as a voellmy fluid the model with entrainment not only improves the prediction of the velocities and flow heights in comparison to measurements but also reproduces the variations in run out distances which characterize avalanches with similar terminal velocities but different masses

superelevation of flowing avalanches around curved channel bends flowing avalanches are those with a dense core of flowing granular material at the base which dominates the dynamics causing friction sometimes when avalanches descend they encounter curved channel bends which cause the flowing material to superelevate or climb up on the wall of the channel bend so that the level of the flowing snow is higher on the outside of the bend than at the center of the channel this can provide important information about avalanche speeds the conventional approach for estimating speeds is mathematically equivalent to one developed from equations based on fluid mechanics with a balance between fluid pressure force and centrifugal force to yield a simple expression which relates channel radius avalanche speed and superelevation geometry in this paper the conventional theory is replaced by one which relates avalanche speed to basal friction as appropriate for flowing snow passive snow pressure accounting for friction between snow particles channel radius and superelevation geometry it is shown that the conventional theory is physically unrealistic for flowing snow modeled as a frictional material also the conventional theory will result in lower speed estimates than the new formulation for the same amount of superelevation

palaeomagnetic rotations and fault kinematics in the rif arc of morocco palaeomagnetic and structural investigations in the rif arc of morocco indicate that there have been large rotations associated with a pattern of outwardly directed thrusting rock magnetic experiments in conjunction with thermal and alternating field demagnetization demonstrate that eight sites in jurassic and cretaceous limestones along the internal external boundary have a stable remanent magnetization this is in most cases rotated anticlockwise by as much as 100 from the expected mesozoic declination but in the tetuan area there are large clockwise rotations kinematic indicators from fault surfaces indicate the following 1 in the eastern rif there has been predominantly south directed thrusting partly overprinted by extensional and sinistral strike slip faults 2 at the eastern end of the n 70 e striking jebha fault zone there is a pattern of dominant sinistral ne trending and subsidiary dextral se trending strike slip faults overprinted by normal faults while at the western end deformation consists largely of south directed thrusting 3 in the northern section of the chain where the structural trends are dominantly n s thrusting is directed w to nw it is suggested that the data are best explained by differential motion and rotation of thrust sheets during outwardly directed thrusting around the arc

microearthquake seismicity and fault plane solutions around the nekor strike slip fault morocco abstract three hundred and twenty eight earthquakes recorded in the course of 5 weeks in 1989 in the central rif of northern morocco provided no evidence for activity on the nekor fault the principal geological structure in the region itself most of the seismicity is located northwest of the nekor fault most of the 41 fault plane solutions show mainly strike slip motion left lateral on n s striking planes with p axes trending n145 this deformation is consistent with the n s trending normal faults caused by the e w quaternary extension and with the present relative nw se convergence between africa and europe the active deformation around the eastern rif is better represented by a distributed shear zone than by a strike slip fault

seismological evidence for a delamination process in the lithosphere under the alboran sea summary the continental collision between the african and eurasian plates in the iberian peninsula is solved with a nw se compression with an extensional basin the alboran sea to explain this paradox several models have been proposed including the subduction process of a lithospheric plate in this study a relocation of the seismicity of the area using a jhd algorithm for the period 1950 1995 has been performed which shows a specific hypocentre pattern that is not compatible with plate subduction in addition the direction of the stresses acting in the area has been determined through a comprehensive study of all existing focal mechanisms together with calculations for 19 new earthquakes with sufficient data to determine the focal solution after considering all these data the absence of intermediate shocks in the central part of the alboran basin and the predominantly thrusting mechanisms at the borders of the basin with pressure axes perpendicular to the front we consider a delamination process as a possible mechanism acting in the area

seismicity and focal mechanisms in south spain abstract recent improvements in regional seismological networks allow a better definition of the seismicity and the determination of focal mechanisms in south spain this region is part of the lithospheric plate boundary between africa and eurasia and shows a continuous seismic activity of moderate magnitude m h h 650 km earthquakes also occurring in the region eight fault plane solutions have been determined that can be related to the tectonics of the area the solutions for the shallow shocks are compatible with regional stresses with horizontal compressions in nw se direction and tensions in e w direction that produce normal faulting along the n30 to 60 w and n10 to 30 e systems of faults the mechanisms of the intermediate depth shocks can be explained in terms of a subduction zone from africa in a nw direction that is under compression

formation of levees troughs and elevated channels by avalanches on erodible slopes snow avalanches are typically initiated on marginally stable slopes with a surface layer of fresh snow that may easily be incorporated into them the erosion of snow at the front is fundamental to the dynamics and growth of snow avalanches and they may rapidly bulk up making them much more destructive than the initial release snow may also deposit at the rear base and sides of the flow and the net balance of erosion and deposition determines whether an avalanche grows or decays in this paper small scale analogue experiments are performed on a rough inclined plane with a static erodible layer of carborundum grains the static layer is prepared by slowly closing down a flow from a hopper at the top of the slope this leaves behind a uniform depth layer of thickness h stop at a given slope inclination due to the hysteresis of the rough bed friction law this layer can then be inclined to higher angles provided that the thickness does not exceed h start which is the maximum depth that can be held static on a rough bed an avalanche is then initiated on top of the static layer by releasing a fixed volume of carborundum grains dependent on the slope inclination and the depth of the static layer three different behaviours are observed for initial deposit depths above h stop the avalanche rapidly grows in size by progressively entraining more and more grains at the front and sides and depositing relatively few particles at the base and tail this leaves behind a trough eroded to a depth below the initial deposit surface and whose maximal areal extent has a triangular shape conversely a release on a shallower slope with a deposit of thickness h stop leads to net deposition this time the avalanche leaves behind a levee flanked channel the floor of which lies above the level of the initial deposit and narrows downstream it is also possible to generate avalanches that have a perfect balance between net erosion and deposition these avalanches propagate perfectly steadily downslope leaving a constant width trail with levees flanking a shallow trough cut slightly lower than the initial deposit surface the cross section of the trail therefore represents an exact redistribution of the mass reworked from the initial static layer granular flow problems involving erosion and deposition are notoriously difficult because there is no accepted method of modelling the phase transition between static and moving particles remarkably it is shown in this paper that by combining pouliquen forterre s j fluid mech vol 453 2002 pp 133 151 extended friction law with the depth averaged unicode stix x1d707 i rheology of gray edwards j fluid mech vol 755 2014 pp 503 544 it is possible to develop a two dimensional shallow water like avalanche model that qualitatively captures all of the experimentally observed behaviour furthermore the computed wavespeed wave peak height and stationary layer thickness as well as the distance travelled by decaying avalanches are all in good quantitative agreement with the experiments this model is therefore likely to have important practical implications for modelling the initiation growth and decay of snow avalanches for hazard assessment and risk mitigation

present day state of stress in northern morocco from focal mechanism analysis abstract the use of focal mechanisms of micro earthquakes and moderate teleseisms in the al hoceima area northern morocco enables the determination of the state of stress in the southern part of the gibraltar arc two different states of stress were determined 1 a ene wsw extension in the imzouren area probably with similar magnitudes of 2 and 1 which may be controlled by pre existing structures and 2 a strike slip regime in beni boucetta tamassint and beni abdallah areas 1 nnw sse 3 ene wsw in the two first areas and 1 ne sw 3 nw se in the latter contrary to recently proposed ideas the mean state of stress determined with the help of moderate teleseisms corresponds to a strike slip regime with a nnw sse oriented main compressional axis and a ene wsw horizontal extension similar to the stress field determined from neotectonic studies and somewhat different from that determined from the el asnam aftershock sequence of 1980