investigating multiple fault rupture at the salar del carmen segment of the atacama fault system northern chile fault scarp morphology and knickpoint analysis this study presents a new geomorphological approach to investigate the past activity and potential seismic hazard of upper crustal faults at the salar del carmen segment of the atacama fault system in the northern chile forearc our contribution is based on the analysis of a large set of topographic profiles and allows extrapolating fault analysis from a few selected locations to distances of kilometers along strike of the fault we detected subtle changes in the fault scarp geometry which may represent the number of paleoearthquakes experienced by the structure and extracted the cumulative and last incremental displacement along strike of the investigated scarps we also tested the potential of knickpoints in channels crossing the fault scarps as markers for repeated fault rupture and proxies for seismic displacement the number of paleoearthquakes derived from our analysis is 2 3 well in agreement with recent paleoseismological investigations which suggest 2 3 earthquakes mw 6 5 6 7 at the studied segments knickpoints record the number of events for about 55 of the analyzed profile pairs only few knickpoints represent the full seismic displacement while most retain only a fraction of the displacement the along strike displacement distributions suggest fault growth from the center toward the tips and linkage of individual ruptures our approach also improves the estimation of paleomagnitudes in case of multiple fault rupture by allowing to quantify the last increment of displacement separately paleomagnitudes calculated from total segment length and the last increment of displacement mw 6 5 7 1 are in agreement with paleoseismological results

seismic constraints on a remnant mesozoic forearc basin in the northeastern south china sea abstract the northeastern of the south china sea scs has undergone tectonic inversion from a mesozoic convergent continental margin to a cenozoic divergent continental margin the remnant subduction related structures such as volcanic arc and forearc basin likely preserve key clues to reveal the dynamic mechanism of this tectonic inversion we applied ocean bottom seismometers obs data combining with multi channel seismic data gravity data drilling data and petrologic observations to reveal geophysical and structural features of the dongsha basin a mesozoic basin in the northeastern scs the mesozoic strata are characterized by large thickness 1 8 km relatively high p wave velocities 3 5 5 5 km s high densities 2 55 2 65 g cm3 alternating folds and thrust faults which are significantly different from the features of cenozoic strata the dongsha basin is flanked by a mesozoic granitic arc to the northwest and an inferred palaeo pacific subduction zone to the southeast indicating that it is geographically located in the mesozoic forearc region considering the similar mesozoic strata detected in the southern margin of the scs and the contemporaneous accretionary complex outcrops observed in the palawan continental terrane we propose that the mesozoic strata in these two regions originated from a common mesozoic forearc basin which was broken by the forearc rifting and subsequently separated by the spreading of cenozoic scs accordingly a continuous palaeo pacific subduction system is reconstructed including the arc forearc accretionary wedge tectonic sequences reviewing the mechanisms of forearc rifting globally and the retreat of volcanic arcs onshore south china we speculate that rollback of the palaeo pacific subduction slab might be one of the causes for the forearc rifting and the initial extension of the scs

gravitational potential energy and regional stress and strain rate fields for continental plateaus examples from the central andes and colorado plateau abstract the commonly observed extension in areas of elevated and thickened crust is an expected consequence of having excess gravitational potential energy gpe compared to the low gpe of the surrounding crust while this conceptual model is well founded it is less clear how well gpe related stress orientations compare quantitatively to observed stress and strain rate orientations and what any inconsistency tells us about the presence of other competing forces we estimate the gpe distribution for the central andes and the greater colorado plateau area using topography and crustal thickness variations respectively and compare the related stress fields with the world stress map as well as with a geodetic strain rate field for the colorado plateau only in both areas deviatoric stresses associated with gpe variations alone cannot fully account for the observed deformation rate field for the central andes only a combination of deviatoric stresses associated with gpe and relative plate motions can account for the near n s tensional stress observed in the peruvian andes and the margin normal compressional stress along the eastern cordillera and sub andean fold and thrust belt the observed deformation field around the colorado plateau shows e w extension largely inconsistent with the deviatoric stresses associated with gpe variations except for the area east of the rio grande rift the ne sw oriented stress observed on the southwestern colorado plateau is consistent with the orientations of tensional deviatoric stresses associated with gpe variations we argue that this consistency could be haphazard stress observations may not reflect the current state of stress due to inherited structure or could result from the relative high strength of colorado plateau that allows for regional gpe variations and possibly basal shear to be more significant forces than far field plate interactions for the central andes and colorado plateau stresses associated with gpe variations have a strong influence on the total stress field and can thus be used to calibrate the overall level of deviatoric stress acting within the lithosphere

permanent deformation caused by subduction earthquakes in northern chile earth s crust is thought to eventually rebound following an earthquake so that deformation is not permanent field analysis in the atacama desert northern chile however identifies numerous large cracks in the crust implying that the crust here has been permanently deformed by thousands of earthquakes that have occurred over the past million years

surface cracks record long term seismic segmentation of the andean margin understanding the long term patterns of great earthquake rupture along a subduction zone provides a framework for assessing modern seismic hazard however evidence that can be used to infer the size and location of past earthquakes is typically erased by erosion after a few thousand years meter scale cracks that cut the surface of coastal areas in northern chile and southern peru preserve a record of earthquakes spanning several hundred thousand years owing to the hyperarid climate of the region these cracks have been observed to form during and or shortly after strong subduction earthquakes are preserved for long time periods throughout the atacama desert demonstrate evidence for multiple episodes of reactivation and show changes in orientation over spatial scales similar to the size of earthquake segments our observations and models show that crack orientations are consistent with dynamic and static stress fi elds generated by recent earthquakes while localized structural and topographic processes infl uence some cracks the strong preferred orientation over large regions indicates that cracks are primarily formed by plate boundary scale stresses namely repeated earthquakes we invert the crack based strain data for slip along the well known iquique seismic gap segment of the margin and fi nd consistency with gravity anomaly based inferences of long term earthquake slip patterns as well as the magnitude and location of the november 2007 tocopilla earthquake we suggest that the meter scale cracks can be used to map characteristic earthquake rupture segments that persist over many seismic cycles which encourages future study of cracks and other small scale structures to better constrain the persistence of asperities in other arid tectonically active regions

viscosity of himalayan leucogranites implications for mechanisms of granitic magma ascent the viscosity of the gangotri himalayan leucogranite has been experimentally determined between 80 o and 1100oc 300 and 800 mpa for meltwater contents of 3 98 and 6 66 wt the melt viscosity is independent of pressure and shows an arrhenian behavior relative to temperature within the range of conditions investigated we present an empirical relation that can be used to determine leucogranite magma viscosities knowing their meltwater content and temperature this relation together with phase equilibria experiments constrain the viscosity of the itimalayan leucogranit s to be around 104 5 pas during their eraplacement these viscosities and the widths of dikes belonging to the feeder system are consistent with the theoretical relationship relating these two parameters and show that the precursor magma of the leucogranite was at near liquidus conditions when emplaced within host rocks with preintmsion temperatures around 350oc calculated terminal asa nt rates for the magma in the dikes are around 1 m s magma cmber assembly time is on ths basis estimated to be less than 100 years for a volume of 150 icm3 in addition the dynamical regime of the magma flow in the dikes was essentially laminar thus allowing preservation of any chemical heterogeneity acquired in the source these results constrain the viscosity of melts f rmed during the first steps of crustal anatexis those involving muscovite breakdown to be alsoround 104 5 pas thus compaction may not be the only mechanism of melt segregation in partially melted crustal rocks in view of the very short timescale inferred for magma ascent and emplacement

joint development in perturbed stress fields near faults abstract field evidence is presented for complex spatial and temporal perturbations of an otherwise systematic joint pattern around faults from well exposed faulted rock platforms joints propagating in perturbed stress fields will curve to follow the directions of the stress field trajectories a progressive change in joint direction is observed from unperturbed regions away from faults to strongly perturbed zones adjacent to faults this indicates that the joint pattern can reflect perturbations of the regional stress field around faults in the examples the stress field perturbations are probably due to points of high friction on the fault plane which concentrate stress and distort the stress field in the surrounding rock the corresponding joints converge at these points and are sub parallel to the fault along the remainder of the fault plane the possibility that a fault plane acts as a free surface contained within an elastic body is considered in this situation the fault plane induces a rotation of the principal stress axes to become either perpendicular or parallel to the fault the free surface model seems to explain the metre scale curvature of joints in the vicinity of existing joints but at the kilometre scale of a large fault plane the model becomes unrealistic unless the fault is open at the earth s surface two examples are investigated from the lias of great britain at nash point and robin hood s bay both comprise sub horizontal strata of relatively homogeneous lithology and bed thickness which provide striking examples of joints developed near faults

active surface cracking in aghajari formation of the azar oil field zagros western iran abstract a very rare case of deformation is described in which surface cracks are being developed in a period of few months over an area of ca 55 km2 in the late miocene early pliocene lahbari member of aghajari formation outcropped in the azar oil field of western iran the cracks are unique because of their activity and their relation to regional tectonic stress field and not to shallow local processes the cracks are almost parallel to the ne sw shortening direction deduced from local folds and are of almost pure tensile nature strike slip faulting in the area is also in kinematic concordance with the cracks which show a nw se extension direction erodibility of the surface geological materials and their downwashing by surface water is affecting the surface morphology very quickly it is suggested that movement of incompetent underlying middle miocene gachsaran formation on a lateral ramp of the zagros foredeep fault and regional active shortening of the sedimentary sequence are responsible for development of the cracks construction of the mohr diagram predicts that maximum depth of the tensile cracks is ca 220 m weak mechanical nature of the lahbari member and transient pore pressure are major contributing factors for the crack development study of these active cracks may help to better understand the process of active and past fracturing in foreland fold thrust belts

forearc basins types geometries and relationships to subduction zone dynamics forearc basins are one of the fundamental sedimentary basins and they preserve various geological phenomena arising from dynamic interactions between subducting and overriding plates along convergent plate boundaries previous studies have proposed descriptive classification schemes for such basins and performed analog experiments and numerical simulations examining basin formation and evolution however the great variability of forearc basins means that a comprehensive understanding of these features remains elusive this paper proposes a new classification scheme for forearc basins from the viewpoints of material transfer between the two plates accretionary or nonaccretionary and the long term strain field in the basin compressional or extensional by using characteristics of 41 modern forearc basins geometric characteristics were also analyzed in order to reveal the relationship to subduction zone dynamics including material transfer at the plate boundary accretion erosion plate convergence configurations and kinematics and the mechanics of strain and its partitioning compressional accretionary type basins which are characterized by landward tilting strata and the landward migration of depocenters show a constant width thickness ratio indicating self similar growth of the basin as the outer wedge builds up extensional accretionary type basins develop normal faults in the basin probably due to a gravitational instability of the outer wedge an increase of sediment flux at the trench may grow the accretionary prism and thicken the subduction channel faster leading to a reduction of basal and internal shear strengths of the outer wedge subsidence caused by crustal thinning characterizes the nonaccretionary type basins which have thin trench fill sediments large forearc slopes steady widths of the outer wedge and variable width thickness ratios of the basins from these results the sediment flux at the trench and the plate boundary can be considered as a dominant factor that determines accretion or erosion of the outer wedge and uplift or subsidence of the outer arc high and that is also responsible for the style of deposition in the forearc basin an increase or decrease of the sediment flux may change the type geometry and deformation manner of the forearc basin the results of this study provide important clues to further our understanding of dynamic interactions between forearc basins and subduction zone processes

isotopic evidence for the source of ca and s in soil gypsum anhydrite and calcite in the atacama desert chile abstract the origin of pedogenic salts in the atacama desert has long been debated possible salt sources include in situ weathering at the soil site local sources such as aerosols from the adjacent pacific ocean or salt encrusted playas salars and extra local atmospheric dust to identify the origin of ca and s in atacama soil salts we determined 34 s and 87 sr 86 sr values of soil gypsum anhydrite and 87 sr 86 sr values of soil calcite along three east west trending transects our results demonstrate the strong influence of marine aerosols on soil gypsum anhydrite development in areas where marine fog penetrates inland results from an east west transect located along a breach in the coastal cordillera show that most soils within 90 km of the coast and below 1300 m in elevation are influenced by marine aerosols and that soils within 50 km and below 800 m in elevation receive 50 of ca and s from marine aerosols 34 s values 14 and 87 sr 86 sr values 0 7083 in areas where the coastal cordillera is 1200 m in elevation however coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced most pedogenic salts from inland soils have 34 s values between 5 0 to 8 0 and 87 sr 86 sr ratios between 0 7070 and 0 7076 these values are similar to average 34 s and 87 sr 86 sr values of salts from local streams lakes and salars 5 4 2 34 s and 0 70749 0 00045 87 sr 86 sr in the andes and atacama suggesting extensive eolian reworking of salar salts onto the surrounding landscape ultimately salar salts are precipitated from evaporated ground water which has acquired its dissolved solutes from water rock interactions both high and low temperature along flowpaths from recharge areas in the andes therefore the main source for ca and s in gypsum anhydrite in non coastal soils is indirect and involves bedrock alteration not surficially on the hyperarid landscape but in the subsurface by ground water followed by eolian redistribution of ground water derived salar salts to soils the spatial distribution of high grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local marine and salar salt supporting arguments for tropospheric nitrogen as the main source for soil nitrate

seismological analyses of the 2010 march 11 pichilemu chile mw 7 0 and mw 6 9 coastal intraplate earthquakes on 2010 march 11 a sequence of large shallow continental crust earthquakes shook central chile two normal faulting events with magnitudes around m w 7 0 and m w 6 9 occurred just 15 min apart located near the town of pichilemu these kinds of large intraplate inland crustal earthquakes are rare above the chilean subduction zone and it is important to better understand their relationship with the 2010 february 27 m w 8 8 maule earthquake which ruptured the adjacent megathrust plate boundary we present a broad seismological analysis of these earthquakes by using both teleseismic and regional data we compute seismic moment tensors for both events via a w phase inversion and test sensitivities to various inversion parameters in order to assess the stability of the solutions the first event at 14 hr 39 min gmt is well constrained displaying a fault plane with strike of n145 e and a preferred dip angle of 55 sw consistent with the trend of aftershock locations and other published results teleseismic finite fault inversions for this event show a large slip zone along the southern part of the fault correlating well with the reported spatial density of aftershocks the second earthquake 14 hr 55 min gmt appears to have ruptured a fault branching southward from the previous ruptured fault within the hanging wall of the first event modelling seismograms at regional to teleseismic distances 10 is quite challenging because the observed seismic wave fields of both events overlap increasing apparent complexity for the second earthquake we perform both point and extended source inversions at regional and teleseismic distances assessing model sensitivities resulting from variations in fault orientation dimension and hypocentre location results show that the focal mechanism for the second event features a steeper dip angle and a strike rotated slightly clockwise with respect to the previous event this kind of geological fault configuration with secondary rupture in the hanging wall of a large normal fault is commonly observed in extensional geological regimes we propose that both earthquakes form part of a typical normal fault diverging splay where the secondary fault connects to the main fault at depth to ascertain more information on the spatial and temporal details of slip for both events we gathered near fault seismological and geodetic data through forward modelling of near fault synthetic seismograms we build a kinematic k 2 earthquake source model with spatially distributed slip on the fault that to first order explains both coseismic static displacement gps vectors and short period seismometer observations at the closest sites as expected the results for the first event agree with the focal mechanism derived from teleseismic modelling with a magnitude m w 6 97 similarly near fault modelling for the second event suggests rupture along a normal fault m w 6 90 characterized by a steeper dip angle dip 74 and a strike clockwise rotated strike 155 with respect to the previous event

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

coseismic extension from surface cracks reopened by the 2014 pisagua northern chile earthquake sequence the a d 2014 pisagua earthquake sequence reactivated ancient surface cracks along the entire rupture length in the northern chilean forearc these subtle brittle strain features that are 50 km above the subduction zone interface in the hyperarid atacama desert record deformation from the single earthquake sequence in this study we document how ancient cracks formed during thousands of plate boundary earthquake cycles were reopened during the 2014 earthquake sequence we show that crack orientations along the rupture length reflect deformation from the m w 8 1 mainshock and from an m w 7 7 aftershock 100 km to the south as documented by displacements calculated from continuous geodetic observations we suggest that cracks form during the passage of surface waves and repeated opening and closing enhance crack aperture the orientation and opening of the oldest cracks in the forearc are indicative of the modal or most common rupture area of major megathrust earthquakes in the region while the long term preservation of cracks may be limited to northern chile similar features likely form during strong earthquakes at other subduction zones and represent permanent forearc deformation

an experimental investigation of the influence of water and oxygen fugacity on differentiation of morb at 200 mpa crystallization experiments were performed at 200mpa in the temperature range 1150 950 c at oxygen fugacities corresponding to the quartz fayalite magnetite qfm and mno mn3o4 buffers to assess the role of water and fo2 on phase relations and differentiation trends in mid ocean ridge basalt morb systems starting from a primitive mgo 9 8 wt and an evolved morb mgo 6 49 wt crystallization paths with four different water contents 0 35 4 7 wt h2o have been investigated in primitive morb olivine is the liquidus phase followed by plagioclase clinopyroxene amphibole is present only at water saturated conditions below 1000 c but not all fluid saturated runs contain amphibole magnetite and orthopyroxene are not stable at low fo2 qfm buffer residual liquids obtained at low fo2 show a tholeiitic differentiation trend the crystallization of magnetite at high fo2 mno mn3o4 buffer results in a decrease of melt feo mgo ratio causing a calc alkaline differentiation trend because the magnetite crystallization temperature is nearly independent of the h2o content in contrast to silicate minerals the calc alkaline differentiation trend is more pronounced at high water contents residual melts at 950 c in a primitive morb system have compositions approaching those of oceanic plagiogranites in terms of sio2 and k2o but have ca na ratios and feo contents that are too high compared with the natural rocks implying that fractionation processes are necessary to reach typical compositions of natural oceanic plagiogranites

strain and rotation rate from gps in tibet anatolia and the altiplano 1 deformation measured by regional gps networks in continental plateaus reflects the geologic and tectonic variability of the plateaus for two collisional plateaus tibet and anatolia and one noncollisional the altiplano we analyze the regional strain and rotation rate by inverting gps velocities to calculate the full two dimensional velocity gradient tensor to test the method we use gridded velocities determined from an elastic block model for the eastern mediterranean middle east region and show that to a first order the deformation calculated directly from the gps vectors provides an accurate description of regional deformation patterns principal shortening and extension rate axes vertical axis rotation and two dimensional 2 d volume strain dilatation are very consistent with long term geological features over large areas indicating that the gps velocity fields reflect processes responsible for the recent geologic evolution of the plateaus differences between geological and gps descriptions of deformation can be attributed either to gps networks that are too sparse to capture local interseismic deformation or to permanent deformation that accrues during strong earthquakes the altiplano has higher internal shortening magnitudes than the other two plateaus and negative 2 d dilatation everywhere vertical axis rotation changes sign across the topographic symmetry axis and is due to distributed deformation throughout the plateau in contrast the collisional plateaus have large regions of quasi rigid body rotation bounded by strike slip faults with the opposite rotation sense from the rotating blocks tibet and anatolia are the mirror images of each other both have regions of positive dilatation on the outboard sides of the rotating blocks positive dilatation in the aegean correlates with a region of crustal thinning whereas that in eastern tibet and yunnan province in china is associated with an area of vertical uplift rollback of the hellenic trench clearly facilitates the rotation of anatolia rollback of the sumatra burma trench probably also enables rotation about the eastern syntaxis of tibet

slip distribution of the 2014 mw 8 1 pisagua northern chile earthquake sequence estimated from coseismic fore arc surface cracks the 2014 mw 8 1 iquique pisagua chile earthquake sequence ruptured a segment of the nazca south america subduction zone that last hosted a great earthquake in 1877 the sequence opened 3 700 surface cracks in the fore arc of decameter scale length and millimeter to centimeter scale aperture we use the strikes of measured cracks inferred to be perpendicular to coseismically applied tension to estimate the slip distribution of the mainshock and largest aftershock the slip estimates are compatible with those based on seismic geodetic and tsunami data indicating that geologic observations can also place quantitative constraints on rupture properties the earthquake sequence ruptured between two asperities inferred from a regional scale distribution of surface cracks interpreted to represent a modal or most common rupture scenario for the northern chile subduction zone we suggest that past events including the 1877 earthquake broke the 2014 pisagua source area together with adjacent sections in a through going rupture

redox state microstructure and viscosity of a partially crystallized basalt melt abstract as measured in air above the glass transition range the viscosity of an alkali basalt increases markedly with time by about two orders of magnitude in 12 h this effect is essentially physical and due to the presence of microcrystals although partial crystallization of the melt into spinel and an sio2 poor pyroxene leads to a considerable enrichment in silica of the residual liquid partial crystallization depends strongly on the initial redox state of samples in that the presence of ferrous iron is required for spinel crystals to form and for pyroxene to nucleate and grow around them other measurements show that the viscosity of the crystal free liquid decreases slightly with increasing ratios r fe2 fe because the differences between samples with r 0 16 and 0 83 amount to about 1 5 and 0 3 log units at 950 and 1400 k respectively comparisons of the viscosities of the residual liquid matrix and of the initially crystal free basalt show that physical effects caused by the presence of microcrystals begin to be observed at a low crystal fraction of 5 vol finally a model of viscosity calculation is developed for the melts which reproduces all data obtained in this work to better than 10

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

a model for calculating the viscosity of natural iron bearing silicate melts over a wide range of temperatures pressures oxygen fugacites and compositions a new general model that takes into account the pressure and redox state effect is presented to calculate melt viscosities of natural fe bearing melts this new model is applicable to melts that span a wide range of temperatures from 733 to 1873 k pressures 0 001 15 kbar h2o content from 0 to 12 3 wt and compositions from ultramafic mafic to silicic melts the accuracy of the model is calculated to be 0 23 log units of viscosity which is within or close to experimental uncertainty the transport properties including glass transition temperature and melt fragility can also be calculated from this model a spreadsheet to calculate the viscosity is provided in an electronic supplement

on the strength of interplate coupling and the rate of back arc convergence in the central andes an analysis of the interseismic velocity field 1 we interpret the interseismic crustal velocity field of the central andes using a simple three plate model in which the andean mountain belt is treated as a rigid microplate located between the nazca and south american soam plates we assume that the euler vectors associated with these plates are strictly coaxial and that the surface velocity field can be decomposed into an elastic loading field driven by locking of the main plate boundary and a smaller contribution associated with back arc convergence we obtain our best fit to the geodetic velocities if the main plate boundary is fully 100 locked between depths of 10 50 km and 8 5 of nazca soam plate convergence is achieved in the back arc by underthrusting of the brazilian shield beneath the subandean zone

the geodetic signature of the earthquake cycle at subduction zones model constraints on the deep processes recent megathrust events in tohoku japan maule chile and sumatra indonesia were well recorded much has been learned about the dominant physical processes in megathrust zones partial locking of the plate interface detailed coseismic slip relocking afterslip viscoelastic mantle relaxation and interseismic loading these and older observations show complex spatial and temporal patterns in crustal deformation and displacement and significant differences among different margins a key question is whether these differences reflect variations in the underlying processes like differences in locking or the margin geometry or whether they are a consequence of the stage in the earthquake cycle of the margin quantitative models can connect these plate boundary processes to surficial and far field observations we use relatively simple cyclic geodynamic models to isolate the first order geodetic signature of the megathrust cycle coseismic and subsequent slip on the subduction interface is dynamically and consistently driven a review of global preseismic coseismic and postseismic geodetic observations and of their fit to the model predictions indicates that similar physical processes are active at different margins most of the observed variability between the individual margins appears to be controlled by their different stages in the earthquake cycle the modeling results also provide a possible explanation for observations of tensile faulting aftershocks and tensile cracking of the overriding plate which are puzzling in the context of convergence compression from the inversion of our synthetic gnss velocities we find that geodetic observations may incorrectly suggest weak locking of some margins for example the west aleutian margin

stress evolution during the megathrust earthquake cycle and its role in triggering extensional deformation in subduction zones abstract great moment magnitude mw 8 0 and larger subduction megathrust earthquakes are commonly followed by increased rates of normal faulting seismicity extensional activity within the subducting slab is amplified when megathrust slip propagates close to the trench and forearc extension is triggered by the largest magnitude mw 8 5 and larger events to better understand these observations we develop an earthquake cycle model with a realistic slab geometry and stresses that are in balance with plate interface slip and bulk viscous relaxation the modeled stresses represent perturbations to the long term background tectonic stress field the steady state inter seismic earthquake cycle stresses are compressive and their magnitudes depend on the interface locking configuration from 25 mpa for a fully locked seismogenic zone to 5 mpa for discrete asperities on an otherwise unlocked plate interface the co seismic slip and corresponding co seismic stress changes are similar in these models independent of the locking configuration the co seismic stress change magnitudes are up to 5 mpa this implies that the earthquake cycle stresses after the mainshock would still be compressive in the case of a continuous seismogenic zone but would be widely reset to zero in the case of discrete asperities models with co seismic slip confined to shallow depths produce tensional stress changes in the slab and the forearc near the trench whereas events rupturing the base of the seismogenic zone produce tensional stress changes limited to region immediately surrounding the rupture the locations of normal faulting aftershocks generally correlate well with the tensional co seismic stress changes greater than 1 mpa following the mainshock rapid afterslip occurring down dip of the megathrust rupture expands the region of relative extension but reduces its magnitude and does not promote additional normal faulting events bulk viscous relaxation does little to the state of stress in the elastic parts of the model continued plate convergence across a re locked interface returns the system to the pre earthquake state of compression

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

tectonics fracturing of rock and erosion 1 we argue that by fracturing rock not by raising it relative to base level tectonics plays its most important role in causing rapid incision of valleys and rapid erosion of hillslopes tectonic deformation riddles the upper crust with fractures which not only provide avenues for water flow and thus promote weathering and further disintegration of rock but also fragment bedrock into debris that is readily extracted and transported by surface processes bends in active faults require straining of adjacent rock masses aftershocks that occur subsequent to slip on primary faults reflect penetrative brittle deformation of the upper crust at least some aftershocks must nucleate or lengthen cracks which contribute to the comminution of these rock masses scaling rules suggest that dimensions of ruptures for very small m 2 earthquakes can be meters or less the gutenberg richter recurrence relationship implies that such earthquakes are common as high magnification seismographs in low noise environments confirm moreover large differences among fault plane solutions for aftershocks show that the small faults on which they occur are not parallel to one another some faults must intersect thus the upper crust in tectonically active regions should be fragmented into blocks down to the scale of boulders or smaller dismembered rock arrives at the earth s surface already prepared to be transported away as a corollary both deeply exhumed lower crust and posttectonic igneous rock never deformed under brittle conditions and not deformed recently should be less susceptible to detachment and subsequent transport than fractured rock

simulation of tensile crack generation by three dimensional dynamic shear rupture propagation during an earthquake 1 as there is no evidence that cracks are created directly in modes ii and iii shear cracks probably occur only along a weakness plane as in a preexisting fault mode i fracture therefore may be an important factor in crack formation during shallow earthquakes a three dimensional shear dynamic rupture process was simulated on the assumption that shear slip occurs only in a preexisting fault and the possibility of introducing new internal cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method dem was used to solve this problem because it can introduce internal tensile cracks the simple slip weakening model was used as the friction law on the preexisting fault for shear rupture propagation for new tensile cracks fracture follows classical griffith theory when the critical value for tensile fracture surface energy is reached the proposed model was used to simulate the rupture process of a strike slip shallow fault results show that the generation of new cracks is affected by rupture directivity in terms of the hypocenter and asperity location as well as by fault geometry with respect to the free surface cracks develop a flower like structure that surrounds the preexisting fault when the asperity is located at less than a certain depth the flower like structure that originates from the top of the fault reaches the free surface we consider that this is the mechanism for forming the flower structure near surface during a strike slip shallow earthquake

the sensitivity of hillslope bedrock erosion to precipitation decoupling the impacts of climate and tectonics on hillslope erosion rates is a challenging problem hillslope erosion rates are well known to respond to changes in hillslope boundary conditions e g channel incision rates through their dependence on soil thickness and precipitation is an important control on soil formation surprisingly though compilations of hillslope denudation rates suggest little precipitation sensitivity to isolate the effects of precipitation and boundary condition we measured rates of soil production from bedrock and described soils on hillslopes along a semi arid to hyperarid precipitation gradient in northern chile in each climate zone hillslopes with contrasting boundary conditions actively incising channels versus non eroding landforms were studied channel incision rates which ultimately drive hillslope erosion varied with precipitation rather than tectonic setting throughout the study area these precipitation dependent incision rates are mirrored on the hillslopes where erosion shifts from relatively fast and biologically driven to extremely slow and salt driven as precipitation decreases contrary to studies in humid regions bedrock erosion rates increase with precipitation following a power law from 1 m ma 1 in the hyperarid region to 40 m ma 1 in the semi arid region the effect of boundary condition on soil thickness was observed in all climate zones thicker soils on hillslopes with stable boundaries compared to hillslopes bounded by active channels but the difference in bedrock erosion rates between the hillslopes within a climate region slower erosion rates on hillslopes with stable boundaries decreased as precipitation decreased the biotic abiotic threshold also marks the precipitation rate below which bedrock erosion rates are no longer a function of soil thickness our work shows that hillslope processes become sensitive to precipitation as life disappears and the ability of the landscape to respond to tectonics decreases copyright 2010 john wiley sons ltd

experimental petrology of the 1991 1995 unzen dacite japan part ii cl oh partitioning between hornblende and melt and its implications for the origin of oscillatory zoning of hornblende phenocrysts high temperature pressure experiments were carried out to determine the chlorine hydroxyl exchange partition coefficient between hornblende and melt in the 1992 unzen dacite cl in hornblende and melt was analyzed by electron microprobe whereas oh in hornblende and melt was calculated assuming anion stoichiometry of hornblende and utilizing the dissociation reaction constant for h2o o 1 4 2 oh in water saturated melt respectively the partition coefficient strongly depends on the mg mg fe ratio of hornblende and is expressed as ln k1 1 4 cl oh hb cl oh melt 1 4 2 37 4 6 mg mg fe hb at 2 3 kbar and 800 850 c the twofold variation in cl content in the oscillatory zoned cores of hornblende phenocrysts in the 1991 1995 dacite cannot be explained by the dependence of the cl oh partition coefficient on the mg mg fe hb ratio and requires c 80 variation of the cl oh ratio of the coexisting melt available experimental data at 200 mpa on cl oh fractionation between fluid and melt suggest that c 1 2 1 8 wt degassing of water from the magma can explain the required 80 variation in the cl oh ratio of the melt the negative correlation between al content and mg mg fe ratio in the oscillatory zoned cores of the hornblende phenocrysts is consistent with repeated influx and convective degassing of the fluid phase in the magma chamber

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

pervasive cracking of the northern chilean coastal cordillera new evidence for forearc extension despite convergence across the strongly coupled seismogenic interface between the south american and nazca plates the dominant neotectonic signature in the forearc of northern chile is arc normal extension we have used 1 m resolution ikonos satellite imagery to map nearly 37 000 cracks over an area of 500 km2 near the salar grande 21 s these features which are best preserved in a ubiquitous gypcrete surface layer have both nontectonic and tectonic origins however their strong preferred orientation perpendicular to the plate convergence vector suggests that the majority owe their formation to approximate east west extension associated with plate boundary processes such as interseismic loading coseismic and postseismic strain and long term instability resulting from subduction erosion similar structures were formed during or shortly after the 1995 mw 8 0 earthquake near the city of antofagasta south of salar grande and in conjunction with the 2001 mw 8 2 8 4 arequipa peru event cracks such as these may form in other forearcs but remain largely unexposed because of vegetative cover or marked fluvial erosion factors that are absent in northern chile as a result of its hyperarid climate

co seismic slip from the 1995 july 30 mw 8 1 antofagasta chile earthquake as constrained by insar and gps observations summary we analyse radar interferometric and gps observations of the displacement field from the 1995 july 30 mw 8 1 antofagasta chile earthquake and invert for the distribution of slip along the co seismic fault plane using a fixed fault geometry we compare the use of singular value decomposition and constrained linear inversion to invert for the slip distribution and find that the latter approach is better resolved and more physically reasonable separate inversions using only gps data only insar data from descending orbits and insar data from both ascending and descending orbits without the gps data illustrate the complimentary nature of gps and the presently available insar data the gps data resolve slip near gps benchmarks well while the insar provides greater spatial sampling the combination of ascending and descending insar data contributes greatly to the ability of insar to resolve the slip model thereby emphasizing the need to acquire this data for future earthquakes the rake distribution of slip and seismic moment of our preferred model are generally consistent with previous seismic and geodetic inversions although significant differences do exist gps data projected in the radar line of sight los and corresponding insar pixels have a root mean square rms difference of about 3 cm comparison of our predictions of vertical displacement and observed uplift from corraline algae have an rms of 10 cm our inversion and previous results reveal that the location of slip might be influenced by the 1987 mw 7 5 event our analysis further reveals that the 1995 slip distribution was affected by a 1988 mw 7 2 event and might have influenced a 1998 mw 7 0 earthquake that occurred downdip of the 1995 rupture our slip inversion reveals a potential change in mechanism in the southern portion of the rupture consistent with seismic results predictions of the satellite los displacement from a seismic inversion and a joint seismic gps inversion do not compare favourably with the insar observations

thermodynamic and rheological properties of rhyolite and andesite melts the heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative enthalpy measurements made between 400 and 1800 k for the glass phases the experimental data agree with empirical models of calculation of the heat capacity for the liquid phases the agreement is less good owing to strong interactions between alkali metals and aluminum which are not currently accounted for by empirical heat capacity models the viscosity of both liquids has been measured from the glass transition to 1800 k the temperature dependence of the viscosity is quantitatively related to the configurational heat capacity determined calorimetrically through the configurational entropy theory of relaxation processes for both rhyolite and andesite melts the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions

a general viscosity model of campi flegrei italy melts abstract viscosities of shoshonitic and latitic melts relevant to the campi flegrei caldera magmas have been experimentally determined at atmospheric pressure and 0 5 gpa temperatures between 840 k and 1870 k and h2o contents from 0 02 to 3 30 wt the concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101 5 103 pa s the micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range 1010 pa s falling sphere experiments were performed at 0 5 gpa in the low viscosity range from 100 35 to 102 79 pa s in order to obtain viscosity data of anhydrous and hydrous melts the combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified vft equation l o g a b t c d t e e x p g w t where is the viscosity in pa s t the temperature in k w the h2o content in wt and a b c d e and g are the vft parameters this model reproduces the experimental data 95 measurements with a 1 standard deviation of 0 19 and 0 22 log units for shoshonite and latite respectively the proposed model has been applied also to a more evolved composition trachyte from the same area in order to create a general model applicable to the whole compositional range of campi flegrei products moreover speed data have been used to constrain the ascent velocity of latitic shoshonitic and trachytic melts within dikes using petrological data and volcanological information geometrical parameters of the eruptive fissure and depth of magma storage we estimate a time scale for the ascent of melt from 9 km to 4 km depth where deep and shallow reservoirs respectively are located in the order of few minutes such a rapid ascent should be taken into account for the hazard assessment in the campi flegrei area

the viscosity of hydrous phonolites and trachytes the 1 atm viscosities of hydrated synthetic iron free phonolite and trachyte melts are reported between 108 4 and 1013 1 pa s for water contents between 0 and 5 wt these show a very strong reduction with increasing water content particularly at low contents empirical formulae are derived for the dependence of viscosity on temperature and water content at magmatic temperatures of about 1100 k and water contents of 5 wt viscosities are about 910 pa s for the phonolite and 1120 pa s for the trachyte comparisons with data on peralkaline rhyolites show that the effects of dissolved water are similar even though the viscosities of the different compositions vary this indicates that the mechanism by which water reduces the viscosities of partially depolymerized aluminosilicate liquids is independent of the alkali alkaline earth element ratio in addition no major change in this pattern is observed whether water dissolves primarily as oh or molecular h2o this suggests that a third water dissolution mechanism may be important in these compositions in addition to si o si bond breaking and dissolution of molecular water

permanent fore arc extension and seismic segmentation insights from the 2010 maule earthquake chile 1 geologists have long known that young normal faults are an important structural element of the andean coastal cordillera but their relationship to the subduction seismic cycle is still unclear some of the largest aftershocks of the 2010 mw 8 8 maule earthquake in central chile were nucleated on upper plate normal faults including the mw 6 9 and 7 0 events of the pichilemu earthquake sequence we use the available coseismic gps displacements moment tensor sums and slip distribution models for the maule earthquake to compute the static strain and stress fields imposed on the upper plate by slip on the subduction interface the extensional strains calculated from coseismic gps and from a moment tensor sum of the pichilemu events have similar orientations and orders of magnitude the normal coulomb stress increment csi on the pichilemu fault has maximum positive stresses as high as 4 9 mpa regionally the maule event produced a semi elliptical radial pattern of static extension and deviatoric tension csi 1 5 mpa along the coastal cordillera enclosing the rupture area this elliptical pattern mimics the trends of the major upper crustal structures the static deformation field produced by a great subduction earthquake is an effective mechanism for generating permanent extension above the seismogenic zone reactivating suitably oriented long lived normal faults we suggest that the semi elliptical outline of the first order structures along the coastal cordillera may define the location of a characteristic long lived megathrust segment this observation implies a persistence at least over the quaternary of great subduction ruptures along the maule segment

viscosity of andesite melts and its implication for magma mixing prior to unzen 1991 1995 eruption abstract the viscosity of an iron bearing melt with composition similar to unzen andesite was determined experimentally in the high 10 9 10 10 5 pa s and low 5 1000 pa s viscosity range using a parallel plate viscometer and the falling sphere method respectively falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 k and 200 to 2000 mpa creep experiments were performed in the temperature range of 747 845 k at 300 mpa the water content of the melt varies from nominally dry to 6 2 wt h 2 o the fe 2 fe tot ratio was determined for each sample in the quenched glass using a colorimetric method pressure has minor influence on the viscosity compared with the effect of temperature water content main compositional parameter controlling the viscosity or with the fe 2 fe tot ratio especially important at low water content of the melt based on our new viscosity data and literature data with measured fe 2 fe tot ratio we propose a new empirical equation to estimate the viscosity in pa s of andesitic melts as a function of temperature t in k water content w in wt and fe 2 fe tot ratio the derived relationship reproduces the experimental data 87 in total in the viscosity range from 10 0 5 to 10 13 pa s with a 1 standard deviation of 0 17 log units however application of this calculation model is limited to fe 2 fe tot fe tot 0 3 and to temperatures above t g moreover in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements the viscosity data are used to interpret mixing processes in the unzen magma chamber prior to 1991 1995 eruption we demonstrate that the viscosities of the rhyolite and andesite melts from the two end member magmas are nearly identical prior and during mixing enabling efficient magma mixing

the rheology of crystal bearing basaltic magmas from stromboli and etna abstract our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics persistent activity displayed by basaltic volcanic systems such as etna and stromboli is governed mainly by the textural evolution and rheological properties of eruptive products here we investigate the high temperature 1131 c

motion on upper plate faults during subduction zone earthquakes case of the atacama fault system northern chile 1 motion on the atacama fault system afs in northern chile is driven by andean subduction zone processes we use two approaches observational and theoretical to evaluate how the afs and other forearc faults responded to coseismic stress induced by one well studied megathrust earthquake the 1995 mw 8 1 antofagasta event we use synthetic aperture radar interferometry insar to search for small scale coseismic and postseismic deformation on individual faults the insar data are ambiguous some images show offset consistent with coseismic faulting on the paposo segment of the afs and others lack such signal the fact that we do not observe the fault like displacement in all coseismic interferograms suggests that atmospheric contamination not tectonic deformation is responsible for the signal to explore the capacity of the earthquake to trigger motion on upper plate faults we use seven published slip maps constrained by geodetic and or seismic data to calculate static and dynamic coulomb stress change csc on faults in the antofagasta region the static csc field varies between models and depends on the distribution of coseismic interplate slip on the basis of the csc distribution predicted by our preferred model constrained by all available data we suggest it was unlikely that the antofagasta earthquake directly triggered normal motion on the afs and the insar data are consistent with this null result field reports of normal faulting related to the earthquake may reflect recent but not coseismic motion or highly localized behavior not representative of the regional coseismic stress field

the combined effects of water and fluorine on the viscosity of silicic magmas abstract the newtonian viscosity of water plus fluorine bearing silicate melt of haplogranitic composition hpg8 has been determined viscosities of hpg8 melt with addition of 3 11 and 4 25 wt of f and up to 3 wt h2o have been obtained using a micropenetration technique in the interval 109 74 to 1011 84 pa s and temperatures varying from 370 to 700 c at ambient pressure determination of the temperature dependence of viscosity from this and previous studies permits the parameterization of the viscosity of melts containing water and fluorine having similar composition within a 0 3 log units standard error the viscosity of water bearing f rich haplogranitic samples is represented by a modified vogel fulcher tammann vft equation which provides a non arrhenian description of the temperature dependence of the viscosity the results of this study indicate that taken individually or together both h2o and f have a strong and similar effect on the viscosity of sio2 rich compositions this similarity between f2o 1 and h2o greatly simplifies the task of predicting viscosity for volatile rich highly silicic magmas the low viscosities of hydrous fluorine bearing granitic melts favour efficient crystallization fractionaction paths for these liquids controlling degassing paths and consequently the eruptive behaviour numerical simulations of eruptive events normally do not take into account the contribution of fluorine this may introduce a significant error in the description of the fluid dynamic properties of magma and therefore in the accurate prediction of eruptive scenarios as well as in hazard assessment studies fluorine unlike water remains dissolved in the melt at high concentrations and low confining pressures the incorporation of fluorine data and the modelling of fluorine bearing viscosity data are therefore of fundamental importance for simulations of magma dynamics and prediction of eruptive scenarios

gps derived deformation of the central andes including the 1995 antofagasta mw 8 0 earthquake in order to study both the interplate seismic loading cycle and the distribution of intraplate deformation of the andes a 215 site gps network covering chile and the western part of argentina was selected monumented and observed in 1993 and 1994 a dense part of the network in northern chile and northwest argentina comprising some 70 sites was re observed after two years in october november 1995 the m w 8 0 antofagasta north chile earthquake of 30th july 1995 took place between the two observations the city of antofagasta shifted 80 cm westwards by this event and the displacement still reached 10 cm at locations 300 km from the trench three different deformation processes have been considered for modeling the measured displacements 1 interseismic accumulation of elastic strain due to subduction coupling 2 coseismic strain release during the antofagasta earthquake and 3 crustal shortening in the sub andes eastward displacement of the sites to the north and to the south of the area affected by the earthquake is due to the interseismic accumulation of elastic deformation assuming a uniform slip model of interseismic coupling the observed displacements at the coast require a fully locked subduction interface and a depth of seismic coupling of 50 km the geodetically derived fault plane parameters of the antofagasta earthquake are consistent with results derived from wave form modeling of seismolog ical data the coseismic slip predicted by the variable slip model reaches values of 3 2 m in the dip slip and 1 4 m in the strike slip directions the derived rake is 66 our geodetic results suggest that the oblique nazca south american plate convergence is accommodated by oblique earthquake slip with no slip partitioning the observed displacements in the back arc indicate a present day crustal shortening rate of 3 4 mm year which is significantly slower than the average of 10 mm year experienced during the evolution of the andean plateau

from decades to epochs spanning the gap between geodesy and structural geology of active mountain belts geodetic data from the global navigation satellite system gnss and from satellite interferometric radar insar are revolutionizing how we look at instantaneous tectonic deformation but the significance for long term finite strain in orogenic belts is less clear we review two different ways of analyzing geodetic data velocity gradient fields from which one can extract strain dilatation and rotation rate and elastic block modeling which assumes that deformation is not continuous but occurs primarily on networks of interconnected faults separating quasi rigid blocks these methods are complementary velocity gradients are purely kinematic and yield information about regional deformation the calculation does not take into account either faults or rigid blocks but where gnss data are dense enough active fault zones and stable blocks emerge naturally in the solution block modeling integrates known structural geometry with idealized earthquake cycle models to predict slip rates on active faults future technological advances should overcome many of today s uncertainties and provide rich new data to mine by providing denser more uniform and temporally continuous observations

generation of porphyritic and equigranular mafic enclaves during magma recharge events at unzen volcano japan mafic to intermediate enclaves are evenly distributed throughout the dacitic 1991 1995 lava sequence of unzen volcano japan representing hundreds of mafic recharge events over the life of the volcano this study documents the morphological textural chemical and petrological characteristics of the enclaves and coexisting silicic host lavas the eruptive products described in this study appear to be general products of magma mingling as the same textural types are seen at many other volcanoes two types of magmatic enclaves referred to as porphyritic and equigranular are easily distinguished texturally porphyritic enclaves display a wide range in composition from basalt to andesite are glass rich spherical and porphyritic and contain large resorbed plagioclase phenocrysts in a matrix of acicular crystals and glass equigranular enclaves are andesitic non porphyritic and consist of tabular medium grained microphenocrysts in a matrix glass that is in equilibrium with the host dacite magma porphyritic enclaves are produced when intruding basaltic magma engulfs melt and phenocrysts of resident silicic magma at their mutual interface equigranular enclaves are a product of a more prolonged mixing and gradual crystallization at a slower cooling rate within the interior of the mafic intrusion

invited review paper neogene to quaternary tectonics of the coastal cordillera northern chile abstract the extreme aridity of the northern chilean coastal cordillera enables the complete preservation of permanent deformation related to the coupling between nazca and south america the region between antofagasta and arica is characterized by four types of late cenozoic structures ew striking reverse faults ns striking normal faults sparse wnw and nnw striking right lateral strike slip faults and unimodal and bimodal populations of surface cracks the ew reverse faults occur only between 19 and 21 40 s latitude and have been active since at least 6 ma to present a march 2007 earthquake demonstrates that this deformation can occur during the interseismic phase of the plate boundary seismic cycle the ns normal faults are most abundant near antofagasta and mejillones and diminish in significance northward several of these faults in both the antofagasta and the salar grande area have been reactivated as reverse faults causing minor topographic inversion we suggest that normal faults move during both interseismic and coseismic deformation and are fundamentally very weak surface cracks are ubiquitous throughout the region and form by both non tectonic and tectonic mechanisms a significant proportion forms during coseismic deformation and thus may be used to identify long lived rupture segments on the plate boundary overall forearc deformation is very slow with permanent strain rates of 1 5 nstrain year and fault slip rates less than 0 5 mm year

diffusion and redox reactions of sulfur in silicate melts although large scale transport in magmas is usually controlled by convection diffusion of sulfur in silicate melts nevertheless plays a crucial role in the kinetics of various magmatic processes the most important process is probably the degassing of magmas and melts initiated by an oversaturation of the melt with respect to dissolved volatiles such oversaturation can be caused in nature i e by decompression when a magma ascends to the earth surface but the degassing of melts is also of major interest for technical applications e g during fining of melts in industrial glass production the kinetics of volcanic eruptions and the fining of glass melts are basically controlled by the dynamics of bubble nucleation and growth and these properties are strongly affected by the diffusion of volatiles from the melt into bubbles nemec 1980a b sparks et al 1994 muller simon 2011 this volume hence understanding the diffusion of volatiles in melts provides a necessary tool for modeling bubble nucleation and growth however the diffusivities of volatiles such as h2o co2 so2 and h2s in the melt do not only affect the degassing rate they may also cause a fractionation of volatiles between gas phase and melt as well due to different diffusivities for instance in hydrous magmas the diffusion of h2o is usually much faster than co2 and sulfur diffusion baker et al 2005 zhang and ni 2010 so rapid disequilibrium removal of bubbles from the melt may cause an artificial enrichment of some components in the bubbles other processes which may be governed by sulfur diffusion in the melts are the dissolution and precipitation of minerals in glass manufacturing crucial problems are the kinetics of dissolution of the raw materials in the melt batch and of

mechanisms controlling rupture shape during subcritical growth of joints in layered rocks during joint propagation the orientation of plume lines on joint faces allows for mapping the path taken by the crack tip line during rupture growth rupture shapes in layered clastic sediments of the devonian catskill delta finger lakes district new york indicate joint growth through three stages where velocity of the tip line v tl varies as a function of the crack tip stress intensity k i the initial stage of growth is characterized by a rupture of approximately circular or elliptical shape that expands from an initiation fl aw with a velocity v tl in some cases primary growth involves self correction where an elliptical rupture redistributes the crack tip stress so that the rupture returns to a more stable circular shape the crack tip line eventually propagates to a bedding interface where properties of either a plastic or a noncohesive bedding interface cause v tl 0 along a portion of the tip line the onset of secondary growth occurs when the rupture tip line intersects both bedding interfaces and splits into two discontinuous segments that propagate synchronously as a single coherent rupture nonuniform nonsystematic v tl eventually interferes with the rupture s ability to grow coherently and thus leads to the transition to tertiary growth characterized by the detachment of the coherent rupture into one or more independently propagating noncoherent tip lines throughout all three stages of rupture growth the k i dependent v tl points to subcritical propagation variation from a smooth to rough plume morphology is consistent with propagation through region i of the subcritical regime with a transition at v tl 10 5 m sec rupture velocity may enter region ii of the subcritical regime but such a broad range of k i must be crossed to reach region iii and quasistatic behavior at the critical stress intensity k ic that region ii acts as a barrier through which few joints pass thus greatly limiting the number of postcritical joints in the catskill delta if not in the crust of the earth

water and the viscosity of andesite melts the viscosity of a synthetic andesite like melt has been measured between 1010 and 1014 p for water contents in the range 0 3 5 wt the very slow kinetics of water exsolution over this viscosity range allowed the measurements to be made at 1 bar with a high precision after a steep viscosity decrease of 5 orders of magnitude for 1 wt h2o an additional 2 5 wt h2o causes a further viscosity decrease of only 2 orders of magnitude these viscosity decreases are qualitatively similar to those observed previously for more silica rich compositions the new data join smoothly with available high temperature measurements made at high pressures on water bearing andesite melts because the intrinsic effects of pressure are as small for water bearing as for water free samples the depressing effect of water on the viscosity of natural andesite melts can be estimated changes in water speciation as a function of either temperature or pressure do not seem to have marked effects on the viscosity although quantitative applications are not yet possible the configurational entropy theory accounts qualitatively for these features

late pliocene age for the atacama desert implications for the desertification of western south america the atacama desert forms one of the major hyperarid deserts of the world previous studies suggest that desertification commenced at 14 ma during global climate desiccation sedimentologic data from middle miocene to upper pliocene successions in the modern atacama desert indicate that a semiarid climate persisted from 8 to 3 ma punctuated by a phase of increased aridity at ca 6 ma as such hyperaridity did not commence until the late pliocene implications are 1 that the rain shadow generated by the andean cordillera has had a minor influence on climate change and 2 that the upwelling north flowing cold humboldt current although important in establishing the generally arid climate of western south america did not control the shift to hyperaridity the formation of the hyperarid atacama desert in the late pliocene accompanied the development of the current phase of aridification in the sahara and namib deserts and is attributed to a phase of global climate cooling

normal and reverse faulting driven by the subduction zone earthquake cycle in the northern chilean fore arc 1 despite its location in a convergent tectonic setting the coastal cordillera of northern chile between 21 s and 25 s is dominated by structures demonstrating extension in the direction of plate convergence in some locations however normal faults have been reactivated as reverse faults complicating the interpretation of long term strain in order to place these new observations in a tectonic context we model stress changes induced on these faults by the subduction earthquake cycle our simulations predict that interseismic locking on the plate boundary encourages normal slip on fore arc faults which may result from elastic rebound due to interplate earthquakes or from seismic or aseismic motion that takes place within the interseismic period conversely stress generated by strong subduction zone earthquakes such as the 1995 mw 8 1 antofagasta event provides a mechanism for the reverse reactivation we document here upper plate fault slip in response to the low magnitude stress changes induced by the subduction earthquake cycle suggests that the absolute level of stress on these faults is very low furthermore seismic hazard analysis for northern chile requires consideration of not only the plate boundary earthquake cycle but also the cycle on fore arc faults that may or may not coincide with the interplate pattern though the relationships between permanent strain and deformation calculated using elastic models remain unclear the compatibility of modeled stress fields with the distribution of fore arc faulting suggests that interseismic strain accumulation and coseismic deformation on the subduction megathrust both play significant roles in shaping structural behavior in the upper plate

petrology and fe ti oxide reequilibration of the 1991 mount unzen mixed magma a dacitic magma 64 5 wt sio2 a mixture of phenocryst rich rhyodacite and an aphyric mafic magma was erupted during the recent 1991 1995 mount unzen eruptive cycle the experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas and the nature of the mixing process the preeruption rhyodacitic magma was at a temperature of 790 20 c according to fe ti oxide phenocryst cores and at a depth of 6 to 7 km 160 mpa according to al in hornblende geobarometry the mafic magma that mixed with the rhyodacite is found as andesitic 54 to 62 wt sio2 enclaves in the erupted magma and was essentially aphyric when intruded phase equilibria indicate that an aphyric andesite at 160 mpa is 1030 c h2o saturated and possibly as high as 1130 c 2 wt h2o the composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt sio2 using these compositions and temperatures the temperature of the unzen magma after mixing is estimated to be at least 850 to 870 c the groundmass fe ti oxide microphenocrysts and those in pargasite bearing reaction zones around biotite phenocrysts both give 890 20 c temperatures the oxide oxide contacts give temperatures of 910 20 c the 900 30 c postmixing temperatures are consistent with phase equilibria experiments which show that the magma was not above 930 c at 160 mpa our fe ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption which is a shorter time than is calculated using available diffusion data there is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma

recent crustal deformation in the antofagasta region northern chile and the subduction process new neotectonic observations along with a detailed aerial photograph analysis allow a new interpretation of the recent tectonic behaviour of the outer forearc in northern chile between 22 5 s and 24 5 s antofagasta region both the coastal cordillera and the mejillones peninsula are under e w extension normal faults dipping east with an almost n s orientation are predominant large scale neogene to recent deformation is characterized by vertical uplift and subsidence related to normal faulting recent kinematics along the atacama fault system including the atacama fault itself are controlled by the regional extensional stress regime and the predominant component of recent displacement along the atacama fault is vertical normal however strike slip components are also observed but with moderate offsets no larger than one to two tens of metres the sense of shear and the ratio between vertical and horizontal offsets vary coherently with the fault azimuth compatible with e w extension oblique slip faulting with normal and left lateral offsets of similar amplitude is observed on the most northeasterly oriented segment of the atacama fault this small left lateral component of displacement and the strike slip motion predicted by models of strain partitioning of the convergence along the atacama fault are in opposite senses this occurs because the stress regime in the coastal region is not compressional but extensional very fresh recent ruptures are numerous especially between 23 s and 24 s and provide clear indications of the occurrence of moderate to large continental earthquakes during the late quaternary as pointed out by several authors indirect lines of evidence suggest active subduction erosion and underplating along the margin of northern chile we propose that part of the long term extension is due to the broad scale flexure of the outer forearc this flexure may be controlled by offshore subsidence caused by subduction erosion near the trench and by onshore uplift related to the underplating of eroded low density material beneath the coastal cordillera neotectonic observations show that the state of stress in the outer forearc remains extensional in a deviatoric sense in the long term however it is proposed that the state of stress has a strong time dependent component which is intimately linked to the subduction seismic cycle the mw 8 0 antofagasta earthquake of 1995 july 30 showed that large subduction earthquakes produce e w extension in the coastal region the overall e w deviatoric extension in the outer forearc should be reduced by interseismic contraction in the period separating two subduction earthquakes this reduction means that continental faults will remain locked and aseismic in the interseismic period of the subduction cycle in agreement with microseismic observations which indicate an absence of shallow crustal seismicity we assume that the amount of extension produced by subduction earthquakes in the coastal area is larger than the cumulative interseismic contraction this occurs because the displacement field generated by subduction earthquakes is concentrated in the outer forearc the e w extension should grow over prepeated subduction seismic cycles and lead to large continental earthquakes occurring within the overriding block simultaneous with large subduction events we show new surface ruptures associated with normal faulting along the atacama fault which were most probably triggered by the 1995 antofagasta subduction earthquake

storage conditions and evolution of andesitic magma prior to the 1991 95 eruption of unzen volcano constraints from natural samples and phase equilibria experiments the compositions of homogenized melt inclusions trapped in plagioclase pl microphenocrysts 40 200 m length from mafic enclaves within dacitic rocks erupted at unzen volcano in 1991 95 were investigated the sio2 contents of the melt inclusions vary from 58 to 70 wt and pl anorthite content is an50 70 the stability fields in terms of temperature and water activity of natural pl and coexisting melts from the melt inclusions were estimated from data of phase equilibria experiments performed with a synthetic andesite composition at t 900 1140 c p 200 mpa log fo2 nno 2 nno and water activity of about 0 1 this composition is representative of the average composition of mafic enclaves from the 1991 95 eruption and nearly identical to the composition of andesitic lavas from 1663 unzen eruption the temperatures and h2o melt concentrations calculated using the compositions of coexisting pl and melt inclusions provide an estimation of the conditions of andesitic magma evolution within the mafic enclaves prior to eruption the formation of melt inclusions in plagioclase microphenocrysts occurred at a maximum temperature of 1010 35 c for a melt containing 2 wt h2o and a minimum temperature of 945 c 30 c for a melt with 4 wt dissolved h2o the compositional range of the melt inclusions indicates that the composition of the mafic enclave was not significantly contaminated by the host magma when inclusions were formed the difference between concentrations of dissolved s up to 0 06 wt and cl up to 0 05 wt in melt inclusions in pl of mafic enclaves and concentrations of s 0 005 wt and cl 0 05 0 11 wt in melt inclusions in phenocrysts of the dacitic magma clearly implies that two distinct sources for s and cl in the 1991 95 eruption of unzen volcano need to be considered sulfur degassing was generated by a release of fluids from the high temperature andesitic magma whereas cl was degassed from the low temperature silicic magma the combination of data from melt inclusions and phase equilibria experiments indicates that the mafic end member magma at unzen was already partially crystallized and contained significant proportions 20 to 40 wt of pl and orthopyroxene opx when melt inclusions started to form since clinopyroxene cpx and magnetite mt crystallize after pl and opx the temperatures derived for the mafic end member magma from coexisting opx cpx and ilm mt pairs do not represent temperatures near to the liquidus assuming that the injected mafic magma was nearly aphyric its initial temperature might have been higher than estimated in previous studies

rheology of bubble bearing magmas abstract the physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830 to 960 c at 1 bar pressure the melt composition is sio 2 64 al 2 o 3 23 and cao 13 wt while bubble volume fractions are 0 0 06 0 13 0 32 0 41 and 0 47 measured newtonian viscosities range from 10 10 to 10 14 dpa s melts with bubble fractions of 0 06 and 0 13 show with increasing temperature t an increasing relative viscosity for t t 850 c for all bubble fractions the viscosity decreases markedly with temperature the observed maximum decrease of the relative viscosity is 75 for a bubble fraction of 0 47 at 907 c at all bubble fractions the viscosity is independent of the applied stress which ranged from 11 to 677 bars no clear indications were observed of non newtonian rheological behavior under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction physical and volcanological implications of these measurements are discussed

zebra stripes in the atacama desert fossil evidence of overland flow abstract some hillslopes in the hyperarid region of the atacama desert in northern chile have surface clasts organized into distinct contour parallel bands separated by bare soil we call the bands zebra stripes due to the contrast between the darkly varnished clasts and the light colored salt rich soil gravel that comprises the zebra stripes is sorted such that the coarsest clasts are at the downslope front and fine progressively upslope how and when the zebra stripes formed are perplexing questions particularly in a region experiencing prolonged hyperaridity using googleearth satellite imagery and field observations we report the first quantitative and qualitative observations of zebra stripes in order to test hypotheses of the mechanisms and timing of their formation we consider soil shrink swell seismic shaking and overland flow as possible formation mechanisms and find that overland flow is the most likely based on cosmogenic 10 be concentrations in surface clasts salt deposition rates from the atmosphere and content in the soils we propose that the salt rich soils began accumulating 10 6 y ago and the zebra stripes formed 10 3 10 4 y at the latest the zebra stripe pattern has been preserved due to the self stabilization of the clasts within the stripes and the continued absence of life which would disturb the surface as seen at a wetter site to the south we conclude that the occurrence of zebra stripes is diagnostic of a set of distinct characteristics of local and or regional precipitation soil hillslope form and bedrock type

the viscosity of shoshonitic melts vulcanello peninsula aeolian islands italy insight on the magma ascent in dikes abstract the viscosity of shoshonitic melts and glasses from vulcanello peninsula vulcano island italy was experimentally determined at temperatures between 733 k and 1673 k the water content of the melts varies from 0 03 to 4 75 wt h 2 o the micropenetration technique was employed at ambient pressure in the high viscosity range 10 9 10 12 pa s falling sphere s experiments were performed at 500 and 2000 mpa in the low viscosity range 10 0 5 10 3 pa s results show a decrease of about 2 orders of magnitude in viscosity if 3 wt of water is added to the dry melt at 1300 k at high temperature the viscosity of vulcanello melts is intermediate between that of andesitic and basaltic melts in contrast at low temperatures 1050 k the shoshonitic melt is characterized by a lower viscosity with respect to the two previous melts the general viscosity models of giordano et al giordano d mangiacapra a potuzak m russell j k romano c dingwell d b di muro a 2006 an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids chemical geology 229 42 56 for dry silicate melts is in good agreement with the experimental data in the high temperature range less than 0 3 log units but shows significant differences in the low temperature range up to 1 1 log units the calculation model for hydrous silicate melts from huy and zhang huy h zhang y 2007 toward a general viscosity equation for natural anhydrous and hydrous silicate melts geochimica et cosmochimica acta 71 403 416 reproduces the new viscosity data in the high temperature range within 0 6 log units but shows as well large discrepancies in the low t range for hydrous melts deviations up to 2 log units thus we propose a specific calculation model to predict the viscosity of the shoshonitic melts as a function of temperature and water content this model reproduces the experimental data 24 measurements with a 1 standard deviation of 0 17 log units the viscosity data are used to constrain the ascent velocity of shoshonitic magmas from vulcanello within dikes using petrological data temperature and crystal content of the magma and volcanological information geometrical parameters of the eruptive fissure and depth of magma storage we estimate the time scale for the ascent of magma from the main reservoir to the surface results show time scales in the order of hours to few days we conclude that the rapid ascent of poorly evolved melts from moho depths should be taken into account for the hazard assessment of vulcano island

constructing forearc architecture over megathrust seismic cycles geological snapshots from the maule earthquake region chile we present new field structural data from the chilean coastal cordillera located above the northern and central parts of the interplate contact ruptured by the a d 2010 m w 8 8 maule earthquake the northern study area contains the northwest striking pichilemu normal fault an intraplate structure reactivated after the megathrust event by crustal earthquakes up to m w 7 0 the structural style of this region is dominated by kilometer scale normal faults that have been active at least throughout the quaternary the orientations of these main faults define three structural systems 1 northeast and 2 northwest striking margin oblique faults and 3 north to north northeast striking margin parallel faults from north to south these three systems vary in their predominant occurrence starting with bimodal orientations of groups 1 and 2 followed by predominantly single north to north northeast orientations of group 3 reverse faults coexist in time and space with the normal structures but are scarce and display variable apparently random orientations the shallow crustal normal faults including the pichilemu fault show a persistent kinematic history probably spanning thousands of subduction seismic cycles though historically smaller in magnitude than those of the triggered normal faults interseismic forearc thrust events were recorded above the rupture area prior to the maule earthquake the quaternary reverse faults identified in our study regions may be preserving interseismic slow strain rate permanent deformation signature in the structural grain analogous observations along the a d 2011 tohoku earthquake rupture in japan imply that such a link between the short and long term deformation patterns of the forearc is not exclusive of the maule earthquake region

southern peru desert shattered by the great 2001 earthquake implications for paleoseismic and paleo el nino southern oscillation records in the desert region around the coastal city of ilo the great southern peru earthquake of june 23 2001 8 2 8 4 moment magnitude produced intense and widespread ground failure effects these effects included abundant landslides pervasive ground cracking microfracturing of surficial hillslope materials collapse of drainage banks over long stretches widening of hillside rills and lengthening of first order tributary channels we have coined the term shattered landscape to describe the severity of these effects long term consequences of this landscape shattering are inferred to include increased runoff and sediment transport during postearthquake rainstorms this inference was confirmed during the first minor postearthquake rainstorm there which occurred in june and july of 2002 greater amounts of rainfall in this desert region have historically been associated with el nino events previous studies of an unusual paleoflood deposit in this region have concluded that it is the product of el nino generated precipitation falling on seismically disturbed landscapes the effects of the 2001 earthquake and 2002 rainstorm support that conclusion

paleoseismology of the mejillones fault northern chile insights from cosmogenic 10be and optically stimulated luminescence determinations 1 we have undertaken the first paleoseismological study on an upper plate fault in chile the selected structure was the mejillones fault which is marked by a conspicuous fault scarp using cosmogenic 10be and osl dating and detailed sedimentary logging of trenches we have constrained the abandonment of two alluvial surfaces by fault activity at ca 35 ka and ca 14 ka based on stratigraphic observation we characterized the fault evolution in four intervals over the last ca 35 ka during the first three intervals the fault had a steady slip rate of 0 61 0 26 m ka the fourth interval is delineated by the last vertical fault slip and the accumulation of un deformed hillslope deposits after ca 3 3 ka and has a slip rate of 0 22 0 06 m ka the younger surface abandonment was caused by two mw 7 paleoearthquakes with a recurrence interval of 5 0 3 5 ka the third interval is characterized by the interaction of hillslope deposits and aseismic slip and or centimeter scale seismic slip events at ca 3 5 ka a last large mw 6 6 earthquake took place the recurrence intervals of large mw 8 5 subduction earthquakes do not appear to be the same as the recurrence intervals of the mw 7 events on the upper plate mejillones fault

the 2008 methoni earthquake sequence the relationship between the earthquake cycle on the subduction interface and coastal uplift in sw greece ah is supported by a shell exploration studentship this study forms part of the nerc and esrc funded project earthquakes without frontiers under grant nej02001x 1 and was partly funded by the nerc grant looking inside the continents from space

viscosity of high k basalt from the 5th april 2003 stromboli paroxysmal explosion abstract the 5th april 2003 paroxysmal event was the strongest explosion that has occurred at stromboli in the last 50 years this event lasted only few minutes and was characterised by two violent explosions followed by gas and pyroclast emission in order to constrain models of the dynamics of the paroxystic event the viscosity of anhydrous and hydrous stromboli high potassium hk basaltic melts have been measured viscosity has been investigated in the low viscosity range with the falling sphere method at superliquidus temperatures 1423 to 1673 k and 0 5 gpa and in the high viscosity range with micropenetration near the glass transition temperature 723 to 1035 k at atmospheric pressure falling sphere experiments were performed in a piston cylinder apparatus with melts whose water content varies from nominally anhydrous 0 02 wt h 2 o to 4 16 wt h 2 o the combination of high and low viscosity data permits a general description of the viscosity as a function of temperature and water contentusing a modified tamman vogel fulcher equation using these new viscosity data an estimation of the flow regime and magma velocity is performed our data suggest that the ascent of magma from the 7 8 km deep reservoir to a shallower reservoir located at about 3 km of depth may occur within minutes moreover we infer a turbulent flow regime finally our estimates of the ascent velocity agree qualitatively with results from petrological studies e g bertagnini a metrich n landi p rosi m 2003 stromboli volcano aeolian archipelago italy an open window on the deep feeding system of a steady state basaltic volcano journal of geophysical research 108 2336 2350 which indicate a turbulent flow regime and rapid ascent velocities such to inhibit volatile loss induced crystallization we conclude that hazard evaluation at stromboli island should incorporate the likelihood of very rapid ascent of less evolved melts from depth

seismic coupling along the chilean subduction zone underthrusting at subduction zones can cause large earthquakes at shallow depths but is accommodated by aseismic creep below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding we have determined the maximum depth of the coupled zone and its variability along the chilean subduction zone the maximum depth of seismic coupling is defined by the depth of large m 6 underthrusting earthquakes that have occurred at the downdip edge of the coupled plate interface earthquake depth is determined with omnilinear waveform inversion of long period p waves the statistical uncertainty in the depth is estimated using bootstrapping omnilinear inversion formally accounts for the scaling incompatibility between the p waveforms and decreases the uncertainty in the depth estimate we have found the depths of 27 earthquakes in the time period from 1961 to 1987 seismic coupling in chile extends down to 48 53 km there is a resolvable change in the maximum depth of coupling around 28 s the region immediately north of this latitude has a coupled zone that extends no deeper than 36 41 km while south of this latitude coupling extends down to 48 53 km this transition is not simply related to the oceanic lithospheric age and plate convergence rate but coincides with a change in several geophysical and geological phenomena with respect to shallower north and deeper south coupling there is a change from active volcanos to no volcanos the dip of the deep slab changes from steep to shallow the thickness of trench sediments changes from thin to thick and the depth of the oceanic basement changes from deeper to shallower at 28 s due to the multiplicity of changes at 28 s there is no clear unique interpretation of what physical mechanism controls the variability in the maximum depth of the seismically coupled zone in chile

young displacements on the atacama fault system northern chile from field observations and cosmogenic 21ne concentrations 1 we present the first numerical age constraint for young deformation of the atacama fault system afs in northern chile the young activity of the afs is expressed by several fault scarps which affects alluvial fan sediments of the eastern side of the coastal cordillera 23 30 23 42 s detailed mapping of alluvial fans reveals a complex relationship between fault motion erosion and alluvial fan development an older group of alluvial fans became inactive prior to the scarp formation younger alluvial fans arising directly from feeder channels and entrenched in the fault scarps posts date the scarp formation the youngest slip on the afs is recorded by headward eroding channels entrenched across the scarp which are in turn displaced vertically 0 3 0 5 m by the fault quartz fragments in four sites on the older inactive fan group were analyzed for cosmogenic 21ne concentrations yielding an average age of 424 151 ka the upper limit for the recent activity of the fault combined with the height of fault scarp we calculate a 0 01 mm yr minimum vertical fault slip rate thus young displacement on the afs is quaternary in age and confined to the late pleistocene