the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

physical properties of tuffs from a scientific borehole at alban hills volcanic district central italy recent seismic swarms and hydrothermal activity suggest that the quaternary volcanic complex of the alban hills may pose a threat to the city of rome a 350 m scientific borehole was therefore drilled into this volcanic area to elucidate its inner structure for the first time wire line logs were run in the borehole in order to characterize the physical properties of the rocks and their variations with depth in particular a detailed sonic log was run to measure the p wave velocity from the well head down to 110 m to further investigate velocity changes we carried out laboratory measurements of p and s elastic wave velocities and fluid permeability at effective pressures up to 70 mpa during both increasing and decreasing pressure cycles on selected core samples representative of the main volcanic units specifically we studied samples from two pyroclastic units representative of two classes of volcanic deposits that are representative of the whole succession i a coarse grained well lithified facies pozzolane rosse unit containing abundant mm to cm lava clasts and crystals and ii a fine grained matrix supported pyroclastic deposit tufo pisolitico di trigoria unit with rare lithic lava clasts and sparse pumice elastic wave velocities reveal significant differences between units and indicate how within the same lithology the different degree of lithification and presence of clasts can affect significantly physical property values the mean laboratory value of the p wave velocity for pozzolane rosse and tufo pisolitico di trigoria units is respectively of 3 75 and 3 2 km s at an effective pressure equivalent to that at the depth at which the sonic velocity was measured under increasing effective pressure a profound influence on the transport properties is observed permeability ranges from the order of 10 18 m 2 for the pozzolane rosse unit to the order of 10 15 m 2 for the tufo pisolitico di trigoria unit in good agreement with the shallow aquifer circulating in the shallower units c 2008 elsevier b v all rights reserved

geochronology and tectonic implications of magmatism and metamorphism southern kootenay arc and neighbouring regions southeastern british columbia part i jurassic to mid cretaceous k ar dates and u pb zircon dates define three periods of igneous activity in the southern kootenay arc 1 emplacement of late synkinematic to post kinematic granodioritic plutons in mid jurassic time 170 165 ma accompanying amphibolite facies regional metamorphism 2 emplacement of post kinematic granitic plutons in mid cretaceous time 100 ma and 3 emplacement of small bodies of syenite in eocene time 50 ma in the western part of the area micas from mid jurassic plutons that yield the oldest k ar dates 158 166 ma also yield plateau shaped 40ar 39ar age spectra age spectra for biotites younger than these but older than 125 ma reflect thermal overprinting in southeastern british columbia the kootenay arc marks the transition from the north american rocks of the cordilleran miogeocline to the tectonic collage of allochthonous terranes that have been accreted to it deformation metamorphism and plutonism recorded in rocks of the southern kootenay arc commenced in mid jurassic time as a co

miocene quaternary structural evolution of the uyuni atacama region andes of chile and bolivia abstract we describe the miocene quaternary geological structural evolution of the region between the salar de uyuni and de atacama andes of chile and bolivia we recognized four main tectonic events based on fold geometry fault kinematics and stratigraphic data the oldest event of miocene age is characterized by folding and reverse faulting of the sedimentary successions with an e w direction of shortening in the northern part of the studied area and a wnw ese shortening in the southern part the following two events of pliocene age are characterized by lower shortening amounts they occurred first by reverse faulting with a nw se trending greatest principal stress 1 computed with striated fault planes and a vertical least principal stress 3 followed by pervasive strike slip faulting with the same nw se trending 1 and a horizontal ne sw 3 the fourth event dating to the late pliocene quaternary is characterized by normal faulting the 3 still trends ne sw whereas the intermediate principal stress 2 exchanged with 1 volcanism accompanied both the contractional transcurrent and extensional tectonic phases the mio pliocene compression appears directly linked to a rapid convergence and an apparently important coupling between the continental and oceanic plates the e w to wnw ese direction of shortening of the miocene structures and the nw se 1 of the pliocene structures seem to be more linked to an intra andean re orientation of structures following the wnw directed absolute motion of the south american plate the extensional deformations can be interpreted as related to gravity forces affecting the highest parts of the volcanic belt in a sort of asymmetrical sw ward collapse of the belt

mechanical basis for low angle normal faulting in the basin and range province low angle normal faults seem to violate the criterion that relates fault dip to stress orientation to explain such faults one must postulate a 45 rotation of principal stress directions at mid crustal depths which is difficult to understand on the basis of previous elastic crust models such a stress rotation is shown to be a natural consequence of a low viscosity lower crust

geology of the matthew creek metamorphic zone southeast british columbia a window into middle proterozoic metamorphism in the purcell basin southwest of kimberley southeastern british columbia the matthew creek metamorphic zone occupies the core of a structural dome in mesoproterozoic rocks of the lower aldridge formation lower purcell supergroup it comprises 1 a core zone of ductilely deformed sillimanite grade metapelites thin foliated mafic sills and sheared quartz plagioclase tourmaline pegmatites and 2 a thin transition zone of ductilely deformed metasediments which marks a textural and metamorphic transition between the core zone and overlying regionally extensive brittlely de formed biotite grade semipelitic lower aldridge formation metasediments and thick moyie sills the core zone and transition zone in combination cover an area of 30 km 2 the deepest exposed rocks in the core zone have a strong foli ation and lineation d1 deformation formed during late m1 metamorphism at conditions of 580 650 c and 3 5 0 5 kbar the timing of this metamorphic structural episode is constrained to the interval 1352 1341 ma based on near concordant u pb ages from monazite in pelitic schist near the mouth of matthew creek later weaker metamor phic and deformation episodes variably overprinted the rocks of the matthew creek metamorphic zone the juxtaposi tion of low grade weakly deformed rocks above high grade strongly deformed rocks across a zone of ductile deformation is interpreted to be due to a subhorizontal shear zone

lithoprobe seismic reflection structure of the southeastern canadian cordillera initial results nearly 270 km of crustal seismic reflection data obtained by lithoprobe in the southern canadian cordillera provide a geometric link between the rocky mountain foreland thrust and fold belt the purcell anticlinorium and the extensional regime superimposed on the crystalline core zone autochthonous north american basement and its overlying deformed and transported cover can be traced from the thrust and fold belt beneath the rocky mountain trench to 20 km depth beneath the central part of the purcell anticlinorium the purcell anticlinorium is cored by foreshortened proterozoic supracrustal rocks that were carried northeastward on a series of west dipping imbricate thrust faults these faults crop out within and east of the anticlinorium and converge downward with subhorizontal detachments above the autochthonous north american basement beneath the western purcell anticlinorium and kootenay arc reflections associated with the purcell stratigraphy and its underlying crystalline basement terminate at about 20 km depth and may be truncated against the east dipping eocene slocan lake fault zone the slocan lake fault zone is clearly imaged from the surface to about 12 km depth and can probably be followed discontinuously to about 25 km depth a west dipping high amplitude reflection from beneath the valhalla gneiss complex outlines the domal geometry of the complex and is probably related to an east verging compressional shear zone

asymmetric growth of collapsed caldera by oblique subsidence during the 2000 eruption of miyakejima japan abstract oblique development of the ring faults reflecting the structural heterogeneities inside the volcano formed many asymmetric structures of miyakejima 2000 ad caldera the asymmetry includes a offset location of the ring faults with respect to the associated shallow magma chamber b unequal outward migration of the caldera wall 600 m at the southeastern rim but only 200 m at the northwestern rim c development of tilted terrace only at the southeastern caldera margin d eruption sites and fumaroles being confined to the southern part of the caldera geophysical data including ground deformation and seismic activity indicates the offset of the location of the magma chamber about 2 km south of the caldera center on the surface the ring faults propagated from the deflating magma chamber obliquely about 30 degrees toward the summit the oblique subsidence of the cylindrical block formed a wider instable zone particularly in the southeastern side of the ring fault that enhanced the larger outward migration of the caldera rim and also caused the formation of the outer half ring fault bordering the tilting slope at the southern part ascending pass of the buoyant magma along the tilted ring faults was concentrated in the southern half of the caldera and consequently the distributions of the eruption sites and fumaroles are localized in the southern half part of the caldera the structure of the miyakejima 2000 caldera with complete development of the ring faults its high roof aspect ratio and oblique subsidence is clearly distinguishable from trapdoor type caldera the oblique development of the ring faults can be controlled by the mechanical contrast between the solidified conduits and surrounding fragile volcanic edifice asymmetric development of the miyakejima caldera shows that the collapsed calderas are potential indicators of the heterogeneous structures inside of the volcano particularly in the case of small size caldera

understanding caldera structure and development an overview of analogue models compared to natural calderas abstract understanding the structure and development of calderas is crucial for predicting their behaviour during periods of unrest and to plan geothermal and ore exploitation geological data including that from analysis of deeply eroded examples allow the overall surface setting of calderas to be defined whereas deep drillings and geophysical investigations provide insights on their subsurface structure collation of this information from calderas worldwide has resulted in the recent literature in five main caldera types downsag piston funnel piecemeal trapdoor being viewed as end members despite its importance such a classification does not adequately examine a the structure of calderas particularly the nature of the caldera s bounding faults and b how this is achieved including the genetic relationships among the five caldera types various sets of analogue models specifically devoted to study caldera architecture and development have been recently performed under different conditions apparatus materials scaling parameters stress conditions the first part of this study reviews these experiments which induce collapse as a result of underpressure or overpressure within the chamber analogue the experiments simulating overpressure display consistent results but the experimental depressions require an exceptional amount of doming seldom observed in nature to form therefore these experiments are not appropriate to understand the structure and formation of most natural calderas the experiments simulating underpressure reveal a consistent scenario for caldera structure and development regardless of their different boundary conditions these show that complete collapse proceeds through four main stages proportional to the amount of subsidence progressively characterized by 1 downsag 2 reverse ring fault 3 peripheral downsag 4 peripheral normal ring fault the second part of this study verifies the possibility that these latter calderas constitute a suitable analogue to nature and consists of a comprehensive comparison of the underpressure experiments to natural calderas this shows that all the experimental structures as well as their progressive development are commonly observed at natural calderas highlighting a consistency between models and nature as the shallow structure of experimental calderas corresponds to a precise architecture at depth it provides a unique key to infer the deeper structure of natural calderas recognizing diagnostic surface features within a caldera will thus allow it to be categorized within a precise structural and evolutionary context the general relationship between the evolutionary stage of a caldera and its d s diameter subsidence ratio allows such a quantification with stage 1 calderas characterized by d s 40 stage 2 by 18 the four stages adequately explain the architecture and development of the established caldera end members along a continuum where one or more end members downsag piston funnel piecemeal trapdoor may correspond to a specific stage while such a continuum is controlled by progressive subsidence specific collapse geometries will result from secondary contributory factors roof aspect ratio collapse symmetry pre existing faults these considerations allow proposing an original classification of calderas incorporating their structural and genetic features

hornblende geobarometry of the nelson batholith southeastern british columbia tectonic implications hornblende geobarometry has been applied to granitic rocks of the middle jurassic nelson batholith british columbia locally containing magmatic epidote geobarometry suggests equilibration pressu

eocene structural development of the valhalla complex southeastern british columbia the valhalla complex a cordilleran metamorphic core complex is a 100 km by 30 km structural culmination within the omineca belt of southeastern british columbia it comprises sheets of granitic orthogneiss ranging in age from 100 to 59 ma with intervening paragneiss of uncertain age and stratigraphic correlation the complex is roofed by the ductile valkyr shear zone and the ductile brittle slocan lake fault zone the upper plate comprises lower grade metasedimentary rocks intruded by middle jurassic plutons the valkyr shear zone and the slocan lake fault zone deform 62 and 59 ma granitic sheets in their footwalls the easterly directed valkyr shear zone is a 2 to 3 km thick zone of distributed ductile strain which is arched over the complex and is exposed around the periphery on the northern western and southern margins the shear zone was active between 59 and 54 ma under amphibolite facies conditions the juxtaposition of upper and lower plates with different structural and metamorphic histories indicates that the valkyr shear zone is a significant structure with large displacement there is evidence to support an easterly rooting direction consistent with an extensional origin its surface breakaway is suggested to be west of the valhalla complex the slocan lake fault zone on the eastern side of the complex is a gently 30 easterly dipping ductile brittle normal fault which roots to the east it was active between 54 and approximately 45 ma and truncates the valkyr shear zone timing and structural relationships indicate that the valkyr shear zone and the slocan lake fault zone are genetically related movement on the ductile valkyr shear zone arching of the complex and displacement on the slocan lake fault zone occurred as a continuum in early to middle eocene time this paper documents the presence of significant eocene ductile strain in the valhalla complex and suggests that the role of extension in this region is more profound than had been previously recognized

detachment faults evidence for a low angle origin the origin of low angle normal faults or detachment faults mantling metamorphic core complexes in the southwestern united states remains controversial if sigma sub 1 is vertical during extension the formation of or even slip along such low angle normal faults is mechanically implausible no records exist of earthquakes on low angle normal faults in areas currently undergoing continental extension except from an area of actively forming core complexes in the solomon sea papua new guinea in light of such geophysical and mechanical arguments w r buck and b wernicke and g j axen proposed models in which detachment faults originate as high angle normal faults but rotate to low angles and become inactive as extension proceeds these models are inconsistent with critical field relations in several core complexes the rawhide fault an areally extensive detachment fault in western arizona propagated at close to its present subhorizontal orientation late in the tertiary extension of the region neither the wernicke and axen nor buck models predict such behavior in fact both models preclude the operation of low angle normal faults the authors recommend that alternative explanations or modifications of existing models are needed to explain the evidence that detachment faults form and operate with gentle dips

stress interaction between magma accumulation and trapdoor faulting on sierra negra volcano galapagos abstract understanding the state of stress within volcanoes and how it changes with active geophysical processes is important to assess when and where magma may propagate to the surface and initiate an eruption observations of volcanic deformation help to constrain parameters of models that can be used to describe these processes and to calculate the resulting stress changes within volcanoes here i use geodetic observations to constrain elastic dislocation models of magma accumulation and faulting at sierra negra volcano galapagos in the years before the october 2005 eruption which was the first eruption at sierra negra since 1979 both insar and gps data document a remarkable story of 5 m pre eruption uplift during 1992 2005 which was accompanied by at least three trapdoor faulting events on an intra caldera fault system in january 1998 april 2005 and just before the eruption in october 2005 the pattern of uplift observed in the insar data from different time periods during 1992 2005 is consistent with filling and pressurization of a 2 2 km deep sill under the caldera modeling results for the trapdoor faulting in april 2005 on the other hand indicate that slip occurred on a thrust fault that dips steeply 71 in towards the center of the caldera and extends from the surface down to the sill at 2 2 km depth independently the calculated stress changes caused by the inflating sill show that the coulomb failure stress change cfs at the fault s location is maximized on a 72 dipping thrust fault agreeing almost exactly with the deformation modeling result and implying that the inflation triggered the faulting the calculations also show that the cfs for optimally oriented faults any strike and dip is significantly larger in the southern part of the caldera where the faulting took place than at any other location the trapdoor faulting in turn relieved the pressure within the sill but caused compression to the south of the faults this suggests that while the faulting provides a mechanism for the sill to thicken and postpone eruptions it also prevents the sill from growing to the south

anisotropy repeating earthquakes and seismicity associated with the 2008 eruption of okmok volcano alaska 1 we use shear wave splitting sws analysis and double difference relocation to examine temporal variations in seismic properties prior to and accompanying magmatic activity associated with the 2008 eruption of okmok volcano alaska using bispectrum cross correlation a multiplet of 25 earthquakes is identified spanning five years leading up to the eruption each event having first motions compatible with a normal fault striking ne sw cross correlation differential times are used to relocate earthquakes occurring between january 2003 and february 2009 the bulk of the seismicity prior to the onset of the eruption on 12 july 2008 occurred southwest of the caldera beneath a geothermal field earthquakes associated with the onset of the eruption occurred beneath the northern portion of the caldera and started as deep as 13 km subsequent earthquakes occurred predominantly at 3 km depth coinciding with the depth at which the magma body has been modeled using geodetic data automated sws analysis of the okmok catalog reveals radial polarization outside the caldera and a northwest southeast polarization within we interpret these polarizations in terms of a magma reservoir near the center of the caldera which we model with a mogi point source sws analysis using the same input processing parameters for each event in the multiplet reveals no temporal changes in anisotropy over the duration of the multiplet suggesting either a short term or small increase in stress just before the eruption that was not detected by gps or eruption triggering by a mechanism other than a change of stress in the system

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

magma chamber volume changes associated with ring fault initiation using a finite sphere model application to the aira caldera japan abstract we have derived an analytical solution expressing the magma chamber volume change required for ring fault caldera initiation in terms of a finite sphere model we consider the conditions by which magma chamber contraction volume reduction could contribute to the initiation of a ring fault at the surface above the chamber using the elastic plastic theory of host rock behaviour the model does not consider underpressure pressure less than lithostatic in the chamber but only magma chamber volume reduction or shrinkage the model is heuristic in the sense that we do not explore the detailed mechanical condition for the volume reduction apart from its being related to magma flow out of the chamber but rather focus on the consequences of the reduction for ring fault initiation and dip the solution obtained for the finite sphere model consists of a leading term that is proportional to the cube of the magma chamber depth and a second term that is proportional to the cube of the magma chamber radius the second term reflects explicitly the effects of a finite source radius whereas the first term corresponds to a solution for a point source model this follows because in a point source model the magma chamber radius is zero so that the second term drops out the equation that plays the key role in obtaining this solution is a linear function relating the radius of the caldera to the magma chamber depth the proportionality coefficient of this equation is dimensionless and depends not only on the elastic constants of the medium but also on the depth d and radius a of the magma chamber given by e a d in addition because this coefficient controls a geometric parameter related to the overall form of the ring fault our results indicate that the ring fault shape and size is decided by the magma chamber depth and size as well as by the host rock elastic properties and angle of internal friction the results indicate that the associated ring fault is inward dipping and that the magma chamber radius can be estimated from the fault radius and dip we applied the analytical solution to the ring fault of the aira caldera in southern kyushu japan the calculations indicate that the aira ring fault could have been initiated at the surface as a result of 2 8 reduction in the volume of a magma chamber with a radius of 4 7 km and at a depth of 9 1 km these results agree with independent information on the aira magma chamber we conclude that the present solution yields useful first order information on magma chambers associated with ring faults

early cretaceous kyanite sillimanite metamorphism and paleocene sillimanite overprint near mount cheadle southeastern british columbia geometry geochronology and metamorphic implications mapping of isograds related to regional amphibolite facies metamorphism constrains a three dimensional model of isogradic surfaces near mount cheadle in the northern shuswap metamorphic complex lat 52 20 n long 119 05 w kyanite and sillimanite coexist in a lens shaped zone bounded by the kyanite out and sillimanite in isogradic surfaces that is 50 km long up to 10 km thick and up to 20 km wide textural equilibrium simple regular geometry of isogradic surfaces and simple mineral assemblages suggest that metamorphism occurred at p t conditions near those of the kyanite sillimanite equilibrium curve reconstruction of isotherms in the kyanite sillimanite zone suggests that the metamorphic field gradient was about 14 c km 1 a 5 km thick staurolite free kyanite zone adjacent to the sillimanite in isograd suggests a pressure range of about 1 5 kbar 1 kbar 100 mpa for bathozone 5 of d m carmichael regional metamorphism was early cretaceous monazite u pb geochronology with quenching in th

temporal changes in the cumulative piecewise gradient of a variant of the gutenberg richter relationship and the imminence of extreme events abstract it is generally found that the relative frequencies of occurrence of earthquakes of different magnitudes in seismogenic zones have a power law distribution for a long term dataset the overall slope of this logarithmically transformed distribution is usually indicated by a best fit straight line and expressed as a b value this slope is stable and normally lies between 0 8 and 1 2 the actual value depending on the region examined and the threshold selected for data completeness the linearity of the distribution can be used to make statistical inferences about the potential for larger events over the long run and with appropriate reservations may even be extrapolated to magnitudes that are beyond recent experience we suggest the same information can also be viewed over shorter intervals in terms of an empirical piecewise distribution with relative frequencies of occurrence at adjacent magnitude steps controlling the local slope of the distribution an emergence through time of an excess number of lower magnitude earthquakes causes temporal changes to appear in the low end piecewise gradients of this distribution a marked excursion away from an overall uniform trend for the particular zone may be indicative of an imminent larger event on two separate occasions in 1982 and 1997 such temporal variations were seen in the magnitude distributions of sequences of events near tobago west indies and used to anticipate subsequent damaging mainshocks the recognition of temporal departures from overall linearity of the magnitude frequency relation in a suitable dataset may thus provide an evidential element that can contribute to earthquake forecasting this phenomenological approach was used in the analysis of the neic global dataset of earthquakes of magnitude 6 1 and bigger for the period 1973 2003 to explore its wider applicability trends in the piecewise gradients of the global data were interpreted as pointing to an imminent great earthquake perhaps exceeding magnitude 8 5 such an event did occur shortly afterwards in the form of the great sumatran earthquake of 2004 12 26 following that event global magnitude production continued to exhibit sharp imbalances in the lower magnitude bins indicating that another similar event was likely the second sumatran earthquake on 2005 03 28 satisfied that projection since that time a magnitude production imbalance persists in the global dataset suggesting the system could be poised to output an earthquake or earthquakes in the magnitude range 8 6 9 0 or even greater this contribution describes the piecewise gradient approach and examines its application to global earthquake data

increasing critical sensitivity of the load unload response ratio before large earthquakes with identified stress accumulation pattern the load unload response ratio lurr method is proposed for short to intermediate term earthquake prediction yin x c chen x z song z p yin c 1995 a new approach to earthquake prediction the load unload response ratio lurr theory pure appl geophys 145 701 715 this method is based on measuring the ratio between benioff strains released during the time periods of loading and unloading corresponding to the coulomb failure stress change induced by earth tides on optimally oriented faults according to the method the lurr time series usually climb to an anomalously high peak prior to occurrence of a large earthquake previous studies have indicated that the size of critical seismogenic region selected for lurr measurements has great influence on the evaluation of lurr in this study we replace the circular region usually adopted in lurr practice with an area within which the tectonic stress change would mostly affect the coulomb stress on a potential seismogenic fault of a future event the coulomb stress change before a hypothetical earthquake is calculated based on a simple back slip dislocation model of the event this new algorithm by combining the lurr method with our choice of identified area with increased coulomb stress is devised to improve the sensitivity of lurr to measure criticality of stress accumulation before a large earthquake retrospective tests of this algorithm on four large earthquakes occurred in california over the last two decades show remarkable enhancement of the lurr precursory anomalies for some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods significant anomalies are found if circular areas are used and are not found if increased coulomb stress areas are used for lurr data selection the unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events

accelerating seismicity and stress accumulation before large earthquakes the stress field that existed before a large earth quake can be calculated based on the known source parame ters of the event this stress field can be used to define a region that shows greater seismic moment rate changes prior to the event than arbitrarily shaped regions allowing us to link two previously unrelated subjects coulomb stress interactions and accelerating seismicity before large earthquakes as an example we have examined all m 6 5 earthquakes in california since 1950 while we illustrate the model using seismicity in california the technique i s general and can be applied to any tectonically active re gion we show that where sufficient knowledge of the re gional tectonics exists this method can be used to aug ment current techniques for seismic hazard estimation

toughness and failure of volcanic edifices abstract major volcanic edifices are of two main types stratovolcanoes composite edifices and basaltic edifices shield volcanoes these types of edifices show several remarkable differences for example while some basaltic edifices erupt very frequently many stratovolcanoes erupt very infrequently also most basaltic edifices have gentle slopes commonly 2 12 whereas stratovolcanoes have steeper slopes particularly in their uppermost parts where the slopes may reach 35 42 there have been various attempts to explain these differences but here the focus is on edifice strength or rather toughness toughness of a material is a measure of its resistance to fracture alternatively for a tough material large amounts of energy are needed to cause failure most quoted material toughness critical energy release rate values for rocks are 20 400 j m 2 for extension fractures such as dykes and 0 01 0 03 mj m 2 for shear fractures such as dip slip faults the related property of critical stress intensity or fracture toughness is for most rocks 0 5 3 mpa m 1 2 these values for material and fracture toughness refer to small essentially homogeneous laboratory rock samples here i present equations for calculating the material toughness in volcanic edifices based on the measured or estimated dimensions of associated large structures such as dykes and faults for typical dykes the calculated material toughness is 1 3 47 mj m 2 with a corresponding stress intensity of 114 690 mpa m 1 2 similarly for a 3 8 km long dip slip fault in an edifice the calculated material toughness is 2 3 mj m 2 and the corresponding stress intensity 150 mpa m 1 2 these results compare well with previous material toughness estimates for large strike slip faults and stress intensity estimates for large dykes generalising these results and using field data as well as materials science results i conclude that stratovolcanoes normally have a much higher material toughness than basaltic edifices this is primarily because of different internal structures a basaltic edifice is made of layers and contacts all of which have essentially similar mechanical properties whereas a stratovolcano is made of layers and contacts many of which have widely different properties accordingly it requires much more energy is more difficult for a fracture to propagate through a stratovolcano than through a basaltic edifice thus contrasting toughnesses may be one principal reason why these edifices differ in slope and in failure frequencies including the number of dyke fed eruptions caldera collapses and landslides

seismic hazard in the marmara sea region following the 17 august 1999 izmit earthquake on 17 august 1999 a destructive magnitude 7 4 earthquake occurred 100 km east of istanbul near the city of izmit on the north anatolian fault this 1 600 km long plate boundary 1 2 slips at an average rate of 2 3 cm yr 1 refs 3 5 and historically has been the site of many devastating earthquakes 6 7 this century alone it has ruptured over 900 km of its length 6 models of earthquake induced stress change 8 combined with active fault maps 9 had been used to forecast that the epicentral area of the 1999 izmit event was indeed a likely location for the occurrence of a large earthquake 9 10 here we show that the 1999 event itself significantly modifies the stress distribution resulting from previous fault interactions 9 10 our new stress models take into account all events in the region with magnitudes greater than 6 having occurred since 1700 ref 7 as well as secular interseismic stress change constrained by gps data 11 these models provide a consistent picture of the long term spatio temporal behaviour of the north anatolian fault and indicate that two events of magnitude equal to or greater than the izmit earthquake are likely to occur within the next decades beneath the marmara sea south of istanbul

analytical models of deformation and residual gravity changes due to a mogi source in a viscoelastic medium abstract the popular mogi model describing deformation due to a small pressurized spherical cavity embedded in a homogeneous elastic half space is shortly reviewed similarities and differences with other isotropic deformation models are discussed and the interpretation of the different volume changes accompanying source inflation is provided the model is then generalized to viscoelastic rheology the overpressure needed within the source to reproduce the large deformation sometimes observed in volcanic regions is found to be strongly dependent on rheological parameters so that reasonably low values may be obtained if the relaxation time of the medium surrounding the source is short months instead of the extremely high values inferred from the elastic theory if the inflation of the source is due to the input of new magma from remote distance the resulting residual gravity change g may be easily computed thanks to the spherical geometry of the source and the density of the newly emplaced material may be inferred from the ratio of g w between the gravity change and the uplift this ratio is independent of the overpressure and the radius of the source which are generally ill defined parameters and is slightly dependent on the relaxation time in the transient phase explicit solutions are shown for a step like overpressure history and for a constant magma supply rate a more realistic model is also proposed in which the viscoelastic properties are restricted to a small spherical volume around the source surrounded by an elastic medium even if an accurate interpretation of deformation and gravity changes in volcanic areas generally requires taking into account topography elastic layering and the triaxial geometry of the inflation source values computed according to the generalized mogi model are compared with observations made during the 1982 84 uplift episode at campi flegrei caldera italy for the sake of illustration

stress control of deep rift intrusion at mauna loa volcano hawaii mauna loa volcano hawaii deforms by a combination of shallow dike intrusions in the rift zones and earthquakes along the base of the volcano but it is not known how the spreading is accommodated in the lower part of the volcanic edifice we present evidence from interferometric synthetic aperture radar data for secular inflation of a dike like magma body at intermediate depth in the southwest rift zone during 2002 to 2005 magma accumulation occurred in a section of the rift zone that was unclamped by previous dikes and earthquakes suggesting that stress transfer plays an important role in controlling subsurface magma accumulation

evolving towards a critical point a review of accelerating seismic moment energy release prior to large and great earthquakes there is growing evidence that some proportion of large and great earthquakes are preceded by a period of accelerating seismic activity of moderate sized earthquakes these moderate earthquakes occur during the years to decades prior to the occurrence of the large or great event and over a region larger than its rupture zone the size of the region in which these moderate earthquakes occur scales with the size of the ensuing mainshock at least in continental regions a number of numerical simulation studies of faults and fault systems also exhibit similar behavior the combined observational and simulation evidence suggests that the period of increased moment release in moderate earthquakes signals the establishment of long wavelength correlations in the regional stress field the central hypothesis in the critical point model for regional seismicity is that it is only during these time periods that a region of the earth s crust is truly in or near a self organized critical soc state such that small earthquakes are capable of cascading into much larger events the occurrence of a large or great earthquake appears to dissipate a sufficient proportion of the accumulated regional strain to destroy these long wavelength stress correlations and bring the region out of a soc state continued tectonic strain accumulation and stress transfer during smaller earthquakes eventually re establishes the long wavelength stress correlations that allow for the occurrence of larger events these increases in activity occur over longer periods and larger regions than quiescence which is usually observed within the rupture zone of a coming large event the two phenomena appear to have different physical bases and are not incompatible with one another

dislocation model for aseismic crustal deformation at hollister california geodetic observations at many active plate margins reveal relatively steady aseismic motion during the time between major earthquakes we model the aseismic motion by the relative motion between several blocks that suffer frictional resistance in the upper crust frictional drag is represented by uniform dislocation on a fault surface we assume that friction occurs only on the upper brittle zone of each block boundary and that frictionless sliding occurs below this zone using a bayesian inversion procedure we invert geodetic data to determine the parameters of the block and dislocation model parameters to be estimated include the two horizontal components of velocity for each block and the dislocation rate dip angle slip angle and width of each rectangular fault patch for hollister we assume five blocks and nine rectangular fault patches rates of length change on 92 lines observed by trilateration make up the data triangulation leveling very long baseline interferometry satellite ranging and global positioning system data can also be easily included in our model our inversion procedure uses prior estimates of all block and fault parameters based on geological and seismological data the block parameters are estimated from geological observations of fault displacement rates while the widths of the fault patches are estimated from earthquake hypocentral depths we choose prior estimates of the dislocation rate to match observed creep rates the estimated block motion is well resolved by the geodetic data and agrees well with the geological estimates this suggests that the block motion is steady on time scales from 10 years to 1 m y the net motion across the san andreas calaveras fault system is 38 3 mm yr oriented s38 e thus some additional displacement possibly offshore is needed to match the rate of 56 mm yr predicted by plate tectonic models the depth of the transition from frictional to free sliding varies considerably from 0 4 km on the southern calaveras to 11 km on the central san andreas fault two segments of the san andreas north of 36 50 and south of 36 40 have the greatest potential for moderate to large earthquakes

patterns of magma flow in segmented silicic dikes at summer coon volcano colorado ams and thin section analysis abstract a complex pattern of magma flow is found in two silicic dikes of a radial swarm at summer coon an eroded stratovolcano in southern colorado the two intrusions are broken into multiple segments that suggest vertical dike propagation however anisotropy of magnetic susceptibility ams measurements and thin section observations suggest that magma flow was often subhorizontal and away from the center of the volcano segments that are proximal to the central intrusion are characterized by magma that flowed steeply upward at the proximal segment extremity then laterally along the segment and finally downward at the distal end of the segment magma flow in offset segment tips located far from the volcano center was subhorizontal towards the adjacent segment implying lateral propagation of segment tips towards one another this observation suggests relatively high driving pressure in distal dike segments as supported by dike thickening with radial distance from the center of the volcano the present study indicates that radial dike evolution at stratovolcanoes is dominated by lateral flow of magma and dike segmentation is a poor magma flow indicator a horizontally propagating radial dike has the potential to cause an eruption low on the flank of a composite cone which poses a significant yet largely unrecognized hazard to population centers and infrastructure that may surround the volcano

deformation history of the nw salient of the eastern ghats mobile belt india abstract the eastern ghats mobile belt of india displays fold thrust belt structure with a prominent salient on its nw margin the salient consists of lathore nappe and turekela klippe that have overthrust the craton to nw the rocks of the nappes have undergone granulite facies metamorphism and multiple phases of folding corresponding to the eastern ghats orogeny prior to thrusting as a result the granulites along the thrust are retrograded to amphibolites and the axial traces of the folds have been truncated against the thrust plane the basal decollement of the fold thrust belt is represented by the terrane boundary shear zone that defines the tectonic margin between the craton and the mobile belt it occurs as a ductile thrust affecting the cratonic basement as well as the mobile belt suggesting that the basement did not behave as a rigid body during thrusting thus the study area is comparable with the caledonide fold thrust belt further two large lateral ramps namely khariar and paikamal lateral ramps have been developed on the decollement at the lithological contact between tonalite trondhjemite gneisses granite gneisses and the latetectonic potassic granites of the craton fault bend folds associate with these ramps too it is suggested that the salient structure of the fold thrust belt is the combined result of 1 lateral ramps on the decollement and 2 differential displacement along the sole thrust due to lateral variation in detachment strength

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

a new statistical test for static stress triggering application to the 1987 superstition hills earthquake sequence over the past several years many investigators have argued that static stress changes caused by large earthquakes influence the spatial and temporal distributions of subsequent regional seismicity with earthquakes occurring preferentially in areas of stress increase and reduced seismicity where stress decreases some workers have developed quantitative methods to test for the existence of such static stress triggering but no firm consensus has yet been reached as to the significance of these effects we have developed a new test for static stress triggering in which we compute the change in coulomb stress on the focal mechanism nodal planes of a set of events spanning the occurrence of a large earthquake we compare the statistical distributions of these stress changes for events before and after the mainshock to decide if we can reject the hypothesis that these distributions are the same such rejection would be evidence for stress triggering we have applied this test to the november 24 1987 elmore ranch superstition hills earthquake sequence and find that those post mainshock events that experienced stress increases of at least 0 01 0 03 mpa 0 1 0 3 bar or that occurred from 1 4 to 2 8 years after the mainshocks are consistent with having been triggered by mainshock generated static stress changes

an observational test of the stress accumulation model based on seismicity preceding the 1992 landers ca earthquake abstract we test the bowman and king bowman d d king g c p 2001a accelerating seismicity and stress accumulation before large earthquakes geophys res lett 28 21 4039 4042 bowman d d king g c p 2001b stress transfer and seismicity changes before large earthquakes c r acad sci paris 333 591 599 stress accumulation model by examining the evolution of seismicity rates prior to the 1992 landers california earthquake the stress accumulation sa model was developed to explain observations of accelerating seismicity preceding large earthquakes the model proposes that accelerating seismicity sequences result from the tectonic loading of large fault structures through aseismic slip in the elasto plastic lower crust this loading progressively increases the stress on smaller faults within a critical region around the main structure thereby causing the observed acceleration of precursory activity a secondary prediction of the sa model is that the precursory seismicity rates should increase first at the edges of the critical region with the rates gradually rising over time at closer distances to the main fault we test this prediction by examining year long seismicity rates between 1960 and 2004 as a function of distance from the landers rupture to quantify the significance of trends in the seismicity rates we auto correlate the data using a range of spatial and temporal lags we find weak evidence for increased seismicity rates propagating towards the landers rupture but cannot conclusively distinguish these results from those obtained for a random earthquake catalog however we find a strong indication of periodicity in the rate fluctuations as well as high correlation between activity 130 170 km from landers and seismicity rates within 50 km of the landers rupture temporally offset 1 5 2 years the implications of this spatio temporal correlation will be addressed in future studies

tectonic domains and exhumation history of the omineca belt in southeastern british columbia from 40ar 39ar thermochronology a large geochronological data set comprising 40ar 39ar and k ar hornblende muscovite biotite and k feldspar rb sr muscovite fission track zircon and apatite and u pb zircon and monazite

geology of the nemo lakes belt northern valhalla range southeast british columbia high grade metasedimentary rocks probably of both early paleozoic and late paleozoic triassic ages underlie an area termed the nemo lakes belt between slocan and arrow lakes in the northern valhalla range southeastern british columbia the rocks have experienced two possibly related periods of major folding phase 1 accompanied and outlasted by metamorphism at p t conditions of 5 0 6 8 kbar 500 680 mpa and 630 680 c involved emplacement of ultramafic rocks major faulting and folding phase 2 involved large scale inclined to upright folds which were dominantly south verging deforming the phase 1 fabric both phases probably occurred in the middle to late jurassic as part of the columbian orogeny rocks lithologically and structurally similar to those of the nemo lakes belt are found across the rodd creek fault near the columbia river and extend the general continuity of the belt into the shuswap metamorphic complex plutonic rocks some of which bracket the movement on the rodd creek fault the

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

ductile nappe extrusion in constrictive strain at the origin of transverse segments of the allochthon boundary thrust in the manicouagan imbricate zone central grenville province quebec abstract separating the parautochthonous and allochthonous belts the allochthon boundary thrust abt is a major lithotectonic boundary that generally runs parallel with the length of the grenville province but with some transverse segments in this contribution we investigate one of these segments the manicouagan imbricate zone miz by adding new field based data supplemented by new u pb deformation ages to a compilation of previous research conducted on both sides of the abt in the region our results reveal striking differences between the footwall and hanging wall of the abt in terms of strain and structures and concludes that the transverse orientation of the abt is not related to folding an updated strain analysis allows us to determine that deformation of the miz was dominated by a constrictive type of strain we build on a previously proposed conceptual model to document ductile extrusion over basement ramps driven by tectonic forcing and lateral density contrast in the upper crust at ca 990 ma the insertion of the hot ductile nappe into partially molten metasediments of the surrounding parautochthonous belt was accommodated by constrictive strain within the former and flattening and transverse folding in the latter

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

a mathematical formulation of accelerating moment release based on the stress accumulation model large earthquakes can be preceded by a period of accelerating seismic activity of moderate sized earthquakes this phenomenon usually termed accelerating moment release has yet to be clearly understood a new mathematical formulation of accelerating moment release is obtained from simple stress transfer considerations following the recently proposed stress accumulation model this model based on the concept of elastic rebound simulates accelerating seismicity from theoretical stress changes during an idealized seismic cycle in this view accelerating moment release is simply the consequence of the decrease due to loading of the size of a stress shadow due to a previous earthquake we show that a power law time to failure equation can be expressed as a function of the loading rate on the fault that is going to rupture we also show that the m value which is the power law exponent can be defined as m d 3 with d a parameter that takes into account the geometrical shape of the stress lobes and the distribution of active faults in the stress accumulation model the power law is not due to critical processes

geochronology and tectonic implications of magmatism and metamorphism southern kootenay arc and neighbouring regions southeastern british columbia part ii mid cretaceous to eocene a north south trending belt of amphibolite facies regional metamorphism parallels the purcell trench transects the kootenay arc and is in part fault bounded towards the axis of this belt progressively higher pressure metamorphic mineral assemblages are exposed in the contact aureoles of post kinematic mid cretaceous 100 ma plutons and in metapelites contours of k ar biotite dates for plutonic rocks 55 95 ma are regular are broadly conformable with metamorphic isograds appear to cross internal intrusive contacts of post kinematic plutons and young towards the highest pressure and temperature regional metamorphic zones within the sillimanite zone most micas yield k ar dates between 40 and 55 ma rb sr muscovite dates for deformed and undeformed pegmatites and for muscovite bearing monzogranite and granodiorite fall between 53 and 84 ma u pb zircon dates for the kaniksu batholith and nearby gneiss of uncertain origin yield a lower concordia intercept of 94 ma micas from mid jurassic and mid

plutonism and the origin of metamorphic core complexes the formation of metamorphic core complexes may be triggered by plutonic activity during episodes of continental extension pulses of ductile deformation have taken place during short lived thermal events initiated by the heat input from intruded plutons sills or dikes such intrusions may be the underlying cause for differential uplift of the footwall during tectonic denudation of metamorphic core complexes fast cooling inferred from 40 ar 39 ar apparent ages may have taken place after periods of magma arrival and need not be the result of rapid erosional or tectonic denudation heterogeneity of 40 ar 39 ar apparent ages can be explained by rapid cooling of deforming mylonites formed at shallow crustal levels in the thermal aureoles of intruded sills or sill swarms under such circumstances apparently isothermal decompression paths may actually link pressure temperature points set during periods of transient mineral growth during and after periods of igneous activity

post laramide and pre basin and range deformation and implications for paleogene 55 25 ma volcanism in central mexico a geological basis for a volcano tectonic stress model at central eastern mexico in the mesa central province there are several ranges that were formed after the k t laramide compression but before the basin and range peak extensional episodes at middle late oligocene two important volcano tectonic events happened during this time interval 1 uplift of crustal blocks exhuming the triassic jurassic metamorphic sequence and formation of basins that were filled with red beds and volcanic sequences and 2 normal faulting and tilting to the ne of these blocks and fanglomerate filling of graben and half graben structures the first event from late paleocene to early eocene was related to nne and nnw oriented dextral strike slip faults these faults were combined with nw se en echelon faulting in these blocks through which plutonism and volcanism occurred the second event lasted from early oligocene to early miocene and coincided with basin and range extension intense volcanic activity occurred synchronously with the newly formed or reactivated old fault systems producing thick sequences of silicic pyroclastic rocks and large domes volcano tectonic peaks occurred in three main episodes during the middle late oligocene in this part of mexico at about 32 30 ma 30 28 ma and 26 25 ma the objectives of this work is to summarize the volcano tectonic events that occurred after the end of the laramide orogeny and before the peak episodes of basin and range faulting and sierra madre occidental oligocene volcanism and to discuss the influence of these events on the following oligocene miocene volcano tectonic peak episodes that formed the voluminous silicic volcanism in the mesa central and hence in the sierra madre occidental a model based upon geological observations summarizes the volcanic tectonic evolution of this part of mexico from the late paleocene to the early miocene

in the shadow of 1857 the effect of the great ft tejon earthquake on subsequent earthquakes in southern california the great 1857 fort tejon earthquake is the largest earthquake to have hit southern california during the historic period we investigated if seismicity patterns following 1857 could be due to static stress changes generated by the 1857 earthquake when post 1857 earthquakes with unknown focal mechanisms were assigned strike slip mechanisms with strike and rake determined by the nearest active fault 13 of the 13 southern california m 5 5 earthquakes between 1857 and 1907 were encouraged by the 1857 rupture when post 1857 earthquakes in the transverse ranges with unknown focal mechanisms were assigned reverse mechanisms and all other events were assumed strike slip 11 of the 13 earthquakes were encouraged by the 1857 earthquake these results show significant correlations between static stress changes and seismicity patterns the correlation disappears around 1907 suggesting that tectonic loading began to overwhelm the effect of the 1857 earthquake early in the 20th century

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

deformation and eruptions at mt etna italy a lesson from 15 years of observations this work was partly funded by ingv and the italian dpc and was supported by asi the preview project and crdc amra dpc ingv flank project providing the funds for the publication fees

large lateral ramps in the eocene valkyr shear zone extensional ductile faulting controlled by plutonism in southern british columbia abstract a 2 5 km high s facing lateral ramp links northern and southern segments of the ductile eocene valkyr extensional shear zone which defines the upper and outer boundary of the valhalla core complex in southern british columbia canada the evolution of the valkyr shear zone and of the lateral ramp is strongly influenced by the setting and geometry of middle jurassic tonalitic plutons and of paleocene eocene leucogranite aplite and pegmatite middle jurassic plutons were emplaced in the region of the valhalla complex as a series of interconnected flatbottomed laccoliths with the basal surfaces of adjacent bodies at the same structural level however on a large scale the southern portion of the laccolithic complex is structurally 2 5 km lower than the northern portion the lower surface of the laccolithic complex formed the upper limit of injection of gently dipping paleocene eocene leucogranite sheets as a consequence the upper margin of leucogranite is 2 5 km structurally lower in the south than in the north during the eocene extensional shear zones propagated along the interface between the upper plate stiffened by the cool strong middle jurassic tonalite and the lower plate made weak and ductile by voluminous hot paleoceneeocene leucogranite sheets the northern and southern segments of the valkyr shear zone propagated at two different structural levels and a lateral ramp formed in the intervening zone the ramp was localized at a rheological change across a s dipping boundary between hot ductile paleocene eocene leucogranite and an adjacent strong middle jurassic pluton maximum displacement of 15 20 km occurs in the central portion of the northern segment of the valkyr shear zone the southern segment has only 1 3 km of displacement this has left the pre eocene geological relationships of the southern valhalla complex and its surrounding rocks nearly intact and it can be demonstrated that the valkyr shear zone formed with a gentle original dip

a reappraisal of the tectonic significance of early tertiary low angle shear zones exposed in the vernon map area 82 l shuswap metamorphic complex southeastern canadian cordillera detailed geological mapping across the shuswap metamorphic complex between latitudes 50 00 n and 50 45 n reveals that superstructure forms a semicontinuous carapace across the complex with minimal evidence of internal thinning near the western margin of the complex superstructure and infrastructure are juxtaposed across low angle 2 km thick ductile shear zones spatially associated with paleocene to early eocene syn kinematic granitic rocks the shear zones which yield upper plate to the west shear sense indicators are interpreted as the northern extension of the okanagan valley fault farther east near the north south axis of the complex superstructure and infrastructure are separated by an attenuated metamorphic section but evidence of noncoaxial strain is lacking discrete detachments were not found steeply dipping normal faults cut low angle shear zones and do not merge with them at depth middle eocene volcanic and sedimentary rocks rest unconformably on metamorphic basement the continuit

thermochronological constraints on the eocene exhumation of the grand forks complex british columbia based on 40ar 39ar and apatite fission track geochronology the grand forks complex gfc is a metamorphic core complex within the composite shuswap complex in the southern omineca belt of the canadian cordillera it is juxtaposed against the surrounding lo

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

the evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from mt etna volcano article i nfo volcanic edifices such as mt etna italy are commonly subject to repeated cycles of stress over time due to the combination of magma emplacement from deep reservoirs to shallow depths and superimposed tectonic stresses such repeated stress cycles lead to anisotropic deformation and an increase in the level of crack damage within the rocks of the edifice and hence changes to their elastic moduli which are a key parameter for reliable modelling of deformation sources we therefore report results of changes in elastic moduli measured during increasing amplitude cyclic stressing experiments on dry and water saturated samples of etna basalt in all experiments the young s modulus decreased by approximately 30 over the total sequence of loading cycles and the poisson s ratio increased by a factor of approximately 3 0 5 microseismicity in terms of acoustic emission ae output was also recorded throughout each experiment our results demonstrate that ae output only re commences during any loading cycle when the level of stress where ae ceased during the unloading portion of the previous cycle is exceeded a manifestation of the kaiser stress memory effect in cycles where no ae output was generated we also observed no change in elastic moduli this result holds for both mechanical and thermal stressing our results are interpreted in relation to measurements of volcano tectonic seismicity and deformation at mt etna volcano

understanding stress and deformation in active volcanoes no eruption no caldera collapse and no large landslide can takeplaceinavolcanounlessitsstateofstressissuitablefortheassociatedtype of rock failure the state of stress in turn results in deformation andbothstressanddeformationdependonthemechanicalpropertiesof the rocks that constitute the volcano understanding stress anddeformation in volcanoes is thus of fundamental importance forunderstanding unrest periods and for accurate forecasting volcanofailure such as may result in large scale lateral and vertical collapsesand eruptions deformation studies in volcanic areas have signi cantly improved both in quality and quantity during the past decade while theinterest of the scienti c community and the volcanological commu nity in particular has primarily been in the description andinterpretation of the deformation especially at active volcanoes new and powerful techniques have recently become available toimprove our understanding of the local stresses and mechanicalproperties of volcanoes and how they relate to surface deformation volcano deformation studies in the last years have of courseincluded standard eld and analytical techniques but in additionthere has been increasing use of advanced analogue and numericalmodels as well as modern geophysical monitoring techniques such asgps and insar all these techniques have contributed to an improvedunderstanding of various aspects of both regional and local volcanodeformation at the regional scale the relationship between tectonicsand magmatism at divergent plate boundaries is now better under stood e g kendall et al 2005 wright et al 2006 and so is thegeneral relationship between arc volcanism and seismicity e g walter and amelung 2007 at a more local scale signi cantimprovements have been made in understanding the mechanics ofmagma chamber rupture e g gudmundsson 2006 dyke propaga tion e g polandetal 2004 gudmundssonetal 2008 thestructureof calderas e g acocella 2007 gottsmann and marti 2008 geshi 2009 the collapse of volcanoes e g cervelli et al 2002 amelunget al 2007 the relationships between volcanic activity and edi cedeformation e g neri et al 2009 the seismicity associated withvolcanism benson et al 2008 and the interactions betweenvolcanoes e g miklius and cervelli 2003 andrew and gudmunds son 2008 these and other studies con rm the crucial importance ofunderstandingdeformationandstressinvolcanicareas asisgenerallyrecognised by the volcanological and tectonic communities oneimportanttopicrelatedtovolcanodeformationandstressthatis still not well understood is how active deformation can be used toforecast eruptions and their behaviour this applies particularly to themechanics of dike emplacement the vast majority of volcaniceruptions are fed by dikes and understanding dike propagation andarrest is necessary so as to mitigate various hazards associated withvolcanic eruptions caldera collapses and landslides in particular major eruptions seismicity and sector collapses pose threats out togreat distances from volcanoes understanding these processes however depends on knowing the more general relationshipsbetween deformation stress and volcanic activity the structure and contents of this special issue are motivatedprimarily by our belief that understanding deformation and stress inactive volcanoes is a necessary condition for reliable forecast ofvolcanic eruptions caldera collapses and large landslides thesetopics all belong to the eld of volcanotectonics also we think thatcorrect interpretation of volcano deformation in terms of localstresses and mechanical properties is fundamental for understandingvolcano behaviour and thereby assessing volcanic hazards this special issue derives from a session on volcanotectonics at the2007eguassemblyinvienna austria thefocusison vemaintopicswithin the eld of volcanotectonics the rst topic concerns generalaspects of volcano deformation stress and failure bonafede andferrari 2009 this volume eggert and walter 2009 this volume gudmundsson 2009 this volume the second topic is collapsecalderas battaglia and hill 2009 this volume jonsson 2009 thisvolume kusumoto and gudmundsson 2009 this volume followedby dike propagation and arrest acocella and neri 2009 this volume contents lists available at sciencedirect

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

intrusion of eccentric dikes the case of the 2001 eruption and its role in the dynamics of mt etna volcano abstract the 2001 eruption represents one of the most studied events both from volcanological and geophysical point of view on mt etna this eruption was a crucial event in the recent dynamics of the volcano marking the passage from a period march 1993 june 2001 of moderate stability with slow continuous flank sliding and contemporaneous summit eruptions to a period july 2001 to present of dramatically increased flank deformations and flank eruptions we show new gps data and high precision relocation of seismicity in order to demonstrate the role of the 2001 intrusive phase in this change of the dynamic regime of the volcano gps data consist of two kinematic surveys carried out on 12 july a few hours before the beginning of the seismic swarm and on 17 july just after the onset of eruptive activity a picture of the spatial distribution of the sin eruptive seismicity has been obtained using the hypodd relocation algorithm based on the double difference dd technique modeling of gps measurements reveals a southward motion of the upper southern part of the volcano driven by a nnw sse structure showing mainly left lateral kinematics precise hypocenter location evidences an aseismic zone at about sea level where the magma upraise was characterized by a much higher velocity and an abrupt westward shift revealing the existence of a weakened or ductile zone these results reveal how an intrusion of a dike can severely modify the shallow stress field triggering significant flank failure in 2001 the intrusion was driven by a weakened surface which might correspond to a decollement plane of the portion of the volcano affected by flank instability inducing an additional stress testified by gps measurements and seismic data which led to an acceleration of the sliding flanks

finite extension and low angle normal faulting andersonian theory for infinitesimal strains predicts that normal faults will form at high angles to the surface in extensional terranes in contrast low angle normal faults are sometimes observed on which tens of kilometers of slip has occurred and moderate angle faults with slip of 5 to 15 km are common a simple extension of the theory to account for the stresses required to drive finite deformation shows that low angles are preferred for large extension on individual faults the formation of low angle faults may require inhomogeneities in stress or material properties but once slip begins on a low angle fault it is likely to continue whereas slip on high angle faults is likely to end after modest slip to be replaced by the formation of new high angle faults

dike induced reverse faulting in a graben normal fault slip of the boundary faults of a graben is commonly attributed to dike induced stresses here however we report for the first time clear field evidence of a large dike induced reverse fault slip on a fault associated with a volcano tectonic graben the measured reverse faulting of at least 5 m occurs in the holocene rift zone of northern iceland the reverse slip has apparently occurred on an existing normal fault as a result of over pressure of a nearby 6 13 m thick 8 ka feeder dike a numerical model of the dike fault interaction supports our interpretation the results indicate that dikes particularly potential feeder dikes may cause large reverse slips on nearby normal faults this conclusion should improve the general understanding of geodetic deformation during volcanic unrest periods and may help forecast dike fed eruptions

age and origin of late jurassic and paleocene granitoids nelson batholith southern british columbia in the middle jurassic nelson batholith southern british columbia young 40ar 39ar ages i e 50 60 ma and distorted isobaric surfaces in the batholith suggest the possibility of paleocene granitic plutonism we present the results of a study undertaken to evaluate this possibility geochemical criteria successfully distinguish a suite of granitoids within the nelson batholith that differ from nelson granites of similar sio2 content the granitoid suite is composed of 71 6 75 7 wt sio2 leucocratic biotite granite and quartz monzonite with strong enrichments in alkaline alkaline earth and rare earth elements nd and pb isotopic compositions suggest that biotite granite and quartz monzonite are not related biotite granite yields a u pb age of 158 9 0 6 ma concordant zircons quartz monzonite crystallized at 61 1 ma based on interpretation of titanite and zircon analyses zircons from this sample lie along a line from 61 to 160 ma and demonstrate the presence of middle jurassic inheritance ba

metamorphic core complexes windows into the mechanics and rheology of the crust metamorphic core complexes are products of normal fault displacements sufficient to exhume rocks from below the brittle ductile transition these faults detachments may initiate within the brittle crust at steep angles but they sole into the ductile middle crust and during displacement rotate to gentler dips due to hanging wall extension the exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping low friction shallow segments of the detachment metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress strain localization and strain rate with decreasing temperature providing a window into physical conditions and deformational processes in the mid crust the metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault in addition to those accompanying exhumation these processes may include diapiric emplacement of gneiss domes or exhumation in a subduction channel and may not be directly related to formation of the core complex factors favouring core complex formation are high gravitational potential energy of the extending crust weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

crustal structure of the valhalla complex british columbia from lithoprobe seismic reflection and potential field data the valhalla complex situated in the omineca crystalline belt in southeastern british columbia is a cordilleran metamorphic core complex bordering the suture zone between quesnellia and north american rocks the region is tectonically interposed between a convergent plate margin along canada s west coast and the stable north american craton and is characterized by a crustal thickness of 35 km high surface heat flux and elevated lower crustal electrical conductivity in this study lithoprobe deep crustal seismic reflection data potential field data and geological constraints have been used to gain a better understanding of crustal structure in the vicinity of the valhalla complex analysis of bouguer gravity and total field aeromagnetic data indicates that mafic oceanic rocks and various syn and post accretionary granitoid plutonic rocks are not major constituents of the upper crust underlying the complex the seismic data reveal a moderately reflective upper crust and image several fault zones

reinterpretation of the ordovician rotations in nw argentina and northern chile a consequence of the precordillera collision early paleozoic paleomagnetic data from nw argentina and northern chile have shown large systematic rotations within two domains one composed of the western puna that yields very large up to 80 counter clockwise rotations and the other formed by the famatina ranges and the eastern puna that shows 40 clockwise rotations around vertical axes in several locations lack of significant rotations in younger rocks constrains this kinematic pattern to have occurred during the paleozoic previous tectonic models have explained these rotations as indicative of rigid body rotations of large para autochthonous crustal blocks or terranes a different but simple tectonic model that accounts for this pattern is presented in which rotations are associated to crustal shortening and tectonic escape due to the collision of the allochthonous terrane of precordillera in the late ordovician this collision should have generated dextral shear zones in the back arc region of the convergent sw gondwana margin where systematic domino like clockwise rotations of small crustal blocks accommodate crustal shortening the western puna block bordering the precordillera terrane to the north might have rotated counterclockwise as an independent microplate due to tectonic escape processes in a fashion similar to the present day relationship between the anatolia block and the arabian microplate

u pb geochronological constraints on the timing of episodic regional metamorphism and rapid high t exhumation of the grand forks complex british columbia abstract the grand forks complex gfc is a fault bounded metamorphic core complex in the southern omineca belt of british columbia canada it experienced prograde metamorphism ranging from upper amphibolite to granulite facies conditions during the mesozoic to early tertiary compressional stage of the cordilleran orogeny peak metamorphism was followed by multi stage exhumation in the early eocene this study provides u pb monazite and zircon constraints on the timing of metamorphic episodes in the gfc and subsequent high t amphibolite facies decompression in the early eocene monazite la icp ms ages from metapelitic gneisses record episodic metamorphism from the late jurassic to paleocene with peak metamorphism occurring between 59 and 50 ma peak metamorphism was followed by rapid near isothermal decompression of the gfc between 52 and 50 ma and leucosome crystallization at 50 ma thermodynamic modeling of metapelites in the system mnnckfmashpyce predicts that monazite was not stable at peak metamorphic conditions consistent with the dominant population of 59 ma ages representing growth along the prograde path most likely at subsolidus conditions growth of widespread high y monazite rims 50 ma is predicted along suprasolidus decompression and cooling paths zircon shrimp ages from igneous bodies in the gfc and hanging wall of the bounding kettle river fault krf suggest ductile deformation related to high t decompression of the gfc was ongoing at 51 ma but had ceased by 50 ma truncated by post kinematic granitoids this high t deformation predates subsequent greenschist facies extension on the overlying krf a pre krf hanging wall ductile shear zone is constrained to 59 51 ma it deforms 59 ma ladybird suite leucogranites and may be related to high t exhumation of the core complex rapid 100 c ma cooling rates are required to accommodate high t amphibolite facies exhumation of the gfc at 52 50 ma followed by low t greenschist facies exhumation at 49 ma

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

fault volcano interactions with broadly distributed stretching in rifts abstract areas undergoing pure extension are typically characterized by the formation of faults and fractures orthogonal to the maximum principal stress in these conditions the presence of a volcano and its magmatic system perturbs the local stress field leading to changes in faulting magnitude and attitude this process has been analyzed in many previous modeling works in which fault volcano interaction have been reproduced with set ups that create extension over a single discontinuity by use of a standard base plate however many natural rifts display broadly distributed extension between main border faults with no discrete discontinuities driving deformation to account for these conditions in this study we improve the previous works by reproducing and analyzing the interaction of tectonic stresses with volcanic edifices in areas characterized by broadly distributed extension in particular we run a set of analogue models which are extended by stretching a basal elastic sheet with this improved set up models are generally consistent with previous ones but better reproduce the geometry and architecture of faulting in rifts leading to improved and more rigorously results to compare with real cases we confirmed that the presence of a volcano and or an intrusive body locally modifies the fault pattern concentrating faulting and curving faults notably the rheological contrast between the intrusion and the host rock leads to faults that follow the outline of the body favoring concentric faults in contrast radial faults are developed by the volcano load the combination of intrusion host rock contrast and volcano loading creates both types of faulting which are recognized in natural examples the geometry of the resulting faults is dependent on the coexistence or not of intrusion and edifice and on their dimensions the results indicate that volcanic edifices have a stronger influence on fault attitude with respect to the presence of intrusions experimental results are compared with some natural cases from the east african rift system finally we suggest that using faulting geometries as a foundation geodetic monitoring and more precise modeling could be used to assess the rift evolution of such extensional magmatic systems

evolution of the stress field in southern california and triggering of moderate size earthquakes a 200 year perspective changes in stress in southern california are modeled from 1812 to 2025 using as input 1 stress drops associated with six large 7 0 7 5 earthquakes through 1995 and 2 stress buildup associated with major faults with slip rates 3 mm yr as constrained by geodetic paleoseismic and seismic measurements evolution of stress and the triggering of moderate to large earthquakes are treated in a tensoffal rather than a scalar manner we present snapshots of the cumulative coulomb failure function acff as a function of time for faults of various strike dip and rake throughout southern california we take acff to be zero everywhere just prior to the great shock of 1812 we find that about 95 of those well located m 6 earthquakes whose mechanisms involve either strike slip or reverse faulting are consistent with the coulomb stress evolutionary model that is they occurred in areas of positive acff the interaction between slow moving faults and stresses generated by faster moving faults significantly advanced the occurrence of the 1933 long beach and 1992 landers events in their earthquake cycles coulomb stresses near major thrust faults of the western and central transverse ranges have been accumulating for a long time future great earthquakes along the san andreas fault especially if the san bernardino and coachella valley segments rupture together can trigger moderate to large earthquakes in the transverse ranges as appears to have happened in the santa barbara earthquake that occurred 13 days after the great san andreas shock of 1812 maps of current acff provide additional guides to long term earthquake prediction

volcanoes as elastic inclusions their effects on the propagation of dykes volcanic fissures and volcanic zones in iceland mechanically many volcanoes may be regarded as elastic inclusions either softer with a lower young s modulus or stiffer with a higher young s modulus than the host rock matrix for example many central volcanoes stratovolcanoes composite volcanoes are composed of rocks that are softer than the crustal segments that host them this is particularly clear in iceland where central volcanoes are mostly made of soft rocks such as rhyolite pyroclastics hyaloclastites and sediments whereas the host rock is primarily stiff basaltic lava flows most active central volcanoes also contain fluid magma chambers and many have collapse calderas fluid magma chambers are best modelled as cavities in three dimensions or holes in two dimensions entire calderas as holes and the ring faults themselves which commonly include soft materials such as breccias as soft inclusions many hyaloclastite basaltic breccias mountains partly buried in the basaltic lava pile also function as soft inclusions modelling volcanoes as soft inclusions or holes we present three main numerical results the first using the hole model shows the mechanical interaction between all the active central volcanoes in iceland and in particular those forming the two main clusters at the north and south end of the east volcanic zone evz the strong indication of mechanical interaction through shared dykes and faults in the northern cluster of the evz is supported by observations the second model using a soft inclusion shows that the torfajokull central volcano which contains the largest active caldera in iceland suppresses the spreading generated tensile stress in its surroundings we propose that this partly explains why the proper rift zone northeast of torfajokull has not managed to propagate through the volcano apparently torfajokull tends to slow down the rate of southwest propagation of the rift zone part of the evz the third model again using a soft inclusion indicates how the lateral propagation of a segment of the 1783 laki fissure became arrested in the slopes of the hyaloclastite mountain laki

an 8 month slow slip event triggers progressive nucleation of the 2014 chile megathrust the mechanisms leading to large earthquakes are poorly understood and documented here we characterize the long term precursory phase of the april 1st 2014 mw8 1 north chile megathrust we show that a group of coastal gps stations accelerated westward eight months before the mainshock corresponding to a mw6 5 slow slip event on the subduction interface 80 of which was aseismic concurrent interface foreshocks underwent a diminution of their radiation at high frequency as shown by the temporal evolution of fourier spectra and residuals with respect to ground motions predicted by recent subduction models such ground motions change suggests that in response to the slow sliding of the subduction interface seismic ruptures are progressively becoming smoother and or slower the gradual propagation of seismic ruptures beyond seismic asperities into surrounding metastable areas could explain these observations and might be the precursory mechanism eventually leading to the mainshock

intermediate term earthquake prediction using precursory events in the new madrid seismic zone abstract earthquake prediction may be possible for some mainshock events the time to failure method described by varnes 1989 and bufe and varnes 1990 uses precursory events foreshocks to define an accelerated energy release curve by fitting an equation to the data a predicted time of failure and magnitude can be calculated until recently this method has been used in only a few studies in tectonically active areas and for moderate to large magnitude mainshock events using the microearthquake network data set from the new madrid seismic zone nmsz which is reasonably complete for earthquakes of magnitude 1 5 in the area of interest the method has yielded predicted values of past events as small as m b 3 5 the network data set used in this evaluation covers the time interval from 29 june 1974 to 20 july 1995 for the nmsz there have been 36 earthquakes of magnitude 3 5 over the 21 yr period in which the network has been operating because precursory events are required for the application of the time to failure method mainshocks that occurred before 1980 do not have enough data to adequately define the accelerated energy release curve therefore we utilized the 26 earthquakes that occurred after 1980 and that had a magnitude 3 5 sixteen of the 26 mainshock events were modeled in most cases the precursory sequences yielded predicted times of failure and magnitudes that were reasonably close to the actual mainshock values the remaining mainshocks including those occurring before 1980 could not be modeled due to either 1 not enough events to adequately define the precursory sequence or 2 interfering events that disrupt the accelerated energy release curve in addition two events were modeled from the nuttli catalog nuttli 1979 along with one that used a combination of both catalogs nineteen earthquakes with magnitudes 3 5 were evaluated using the time to failure method the first calculation using the time to failure method gave predicted results with large error bounds essentially no upper bound on the predicted magnitude an empirical relationship between parameters has helped to constrain the range of the predicted magnitude and to a lesser extent the estimated time of failure this relationship modifies the time to failure equation and yields predicted values for magnitudes that have an upper limit another empirical relationship suggests that the logarithm of the moment of the mainshock increases linearly with the logarithm of the size of the precursory event search diameter the relative seismicity of the region also influences the optimum search diameter used to find precursory events in addition to the evaluation of the acceleration sequences associated with the mainshocks an analysis of the occurrence of false positive acceleration sequences acceleration sequences that do not end in a mainshock was conducted the preliminary false positive analysis was conducted by randomly selecting potential mainshock locations the results yielded a false positive acceleration sequence occurrence rate of 2 with the incorporation of the empirical relationships into the time to failure method the potential for future intermediate term earthquake predictions for the nmsz is encouraging

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

evolution of moderate seismicity in the san francisco bay region 1850 to 1993 seismicity changes related to the occurrence of large and great earthquakes the rate of seismic activity of moderate size m 5 5 earthquakes in the san francisco bay sfb region has varied considerably during the past 150 years as measured by the rate of seismic moment release seismic activity in the sfb region is observed to accelerate prior to m 7 0 earthquakes in 1868 1906 and 1989 and then to decelerate following them we examine these seismicity changes in the context of the evolution of the stress field in the sfb region as a result of strain accumulation and release using a model of dislocations in an elastic halfspace we use a coulomb failure function cff to take into account changes in both shear and normal stresses on potential failure planes of varying strike and dip in the sfb region we find that the occurrence of a large or great earthquake creates a stress shadow a region where the stress driving earthquake deformation is decreased interseismic strain accumulation acts to reverse this process gradually bringing faults in the sfb region out of the stress shadow of a previous large or great earthquake and back into a state where earthquake failure is possible as the stress shadow generated by a large or great earthquake disappears it migrates inward toward the fault associated with that large or great event the observed changes in the rate of occurrence of moderate earthquakes in the sfb region are broadly consistent with this model in detail the decrease in seismicity throughout most of the sfb region and a localized increase in the monterey bay region following the great 1906 earthquake is consistent with our predicted stress changes the timing and location of moderate size earthquakes when the rate of seismicity increases again in the 1950s is consistent with areas in which the 1906 stress shadow had been eliminated by strain accumulation in the sfb region those earthquakes that are most inconsistent with our stress evolution model including the 1911 earthquake southeast of san jose are found to occur in regions where dip slip faulting is common in addition to strike slip the 1906 earthquake brought that zone of dip slip faulting closer to failure suggesting that the 1911 event may have been a reverse faulting earthquake rather than a strike slip one similar to the 1984 morgan hill earthquake the occurrence of activity on faults very close to the san andreas such as the lake elsman earthquakes of 1988 and 1989 appear to be associated with the last disappearence of the stress shadow on the loma prieta segment of the san andreas fault thus events of that type may represent an intermediate term precursor to a large earthquake such as the 1989 loma prieta event much of the moderate size earthquake activity in the sfb region appears to be modulated in time by the buildup and release of stress in large and great earthquakes a tensorial approach to earthquake prediction i e taking into account changes in the components of the stress tensor has several advantages over examining scalar changes such as those in seismic activity and moment release rates this tensorial approach allows for both activation and quiescence but in different subregions prior to as well as after large earthquakes

structural and metamorphic constraints on ca 70 ma deformation of the northern valhalla complex british columbia implications for the tectonic evolution of the southern omineca belt abstract penetrative deformation occurred ca 70 ma ago throughout the northern valhalla complex in valhalla and passmore domes and in the gwillim creek shear zone exposed at the deepest structural levels in both domes intense strain s t in the gwillim creek shear zone domain ii was synchronous with and outlasted deformation d 2 throughout the northern complex domain i upper amphibolite facies peak mineral assemblages define the predominant foliation temperature and pressure results determined from microdomains with established relationships to reaction textures and microstructures provide constraints on conditions under which deformation occurred deformation was synchronous with and outlasted peak metamorphic conditions at all structural levels peak conditions of 825 c and 730 mpa and 850 c and 840 mpa were determined for domains i and ii respectively this was followed by cooling and retrograde garnet breakdown at conditions of 715 c and 490 mpa and 765 c and 730 mpa in domains i and ii respectively the faster cooling rate per kilometer of exhumation for domain ii relative to domain i is consistent with a model of conductive cooling via thrusting of domain ii on to a cold footwall metamorphism is interpreted to have resulted from crustal thickening and burial to depths of ca 25 km based on an inferred clockwise p t path and the paucity of late cretaceous intrusions lack of retrograde metamorphism throughout the complex and the high degree of annealing of microstructures indicates that the rocks remained above greenschist facies conditions until they were exhumed in the early tertiary on the valkyr slocan lake extensional shear zone system previous workers have determined that the peak of metamorphism occurred at 72 67 ma in a restricted locality in the core of passmore dome near vallican our study links this dated metamorphism with the structural evolution and metamorphic history throughout the area and shows that supracrustal rocks at all structural levels in valhalla and passmore domes underwent the same metamorphic and deformation event as those near vallican therefore we assign a ca 70 ma age to the penetrative high temperature deformation in northern valhalla complex and the gwillim creek shear zone this coincides with a major period of shortening in the rocky mountains of the foreland belt strain in northern valhalla complex may represent a local transient shear zone that accommodated crustal thickening in the hinterland during orogen scale compression or it may be an exhumed part of the basal detachment of the rocky mountains

fold thrust belt structure of the proterozoic eastern ghats mobile belt a proposed correlation between india and antarctica in gondwana abstract the proterozoic eastern ghats mobile belt along the east coast of india shares a thrusted lower contact with the surrounding cratons the thrust known as the terrane boundary shear zone is associated with two large lateral ramps resulting in a curved outline on the northwestern corner of the mobile belt the eastern ghats mobile belt is divided into two lithotectonic units the lathore group and the turekela group based on their lithological assemblages and deformational history on the basis of published data from a deep seismic sounding dss profile of the eastern ghats crust the terrane boundary shear zone is considered to be listric in nature and acts as the sole thrust between craton and mobile belt the lathore and turekela groups are nappes with this structural configuration the nw part is described as a fold thrust belt however the thrusting postdates folding and granulite metamorphism that occurred in the eastern ghats as in the caledonide type of fold thrust belt of nw scotland the terrane boundary shear zone is interpreted to be contiguous with the rayner napier boundary of the enderby land in a gondwana assembly

the southern omineca belt british columbia new perspectives from the lithoprobe geoscience program geological isotopic and geochronology studies carried out by university and government researchers concurrently with the lithoprobe program have greatly refined our understanding of the regional geology crustal structure and tectonics of the omineca belt sound correlations have been established between surface geology and seismic reflection data cretaceous eocene thrust faults that are imaged in the subsurface in the shuswap complex may be part of a break forward thrust system that feeds into the purcell anticlinorium and the foreland belt the monashee decollement is the western continuation of the sole thrust beneath the foreland belt and provides a means of linking shortening across the entire orogen the thermal peak of metamorphism in the central and southern shuswap complex is now known to have occurred in the late cretaceous paleogene in contrast with earlier held views north american basement rocks are now known to extend beneath the eastern half of the canadian cordillera geochronology

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes