source parameters and scaling relations for small earthquakes in the matsushiro region southwest honshu japan abstract using near field broadband data from a suite of crustal earthquakes which occurred in a small homogeneous source region we examine the scaling relationships among source parameters for earthquakes in the critical 1 5 to 4 5 magnitude range we take special precautions to insure that our conclusions are not biased by local structure seismic moment fault radius and stress drop relations were determined for 32 small shallow strike slip earthquakes 1 6 m l 4 3 in the matsushiro region of southwest honshu japan spectral and cepstral analyses of short period arrivals exhibit structure interpreted as resulting from reverberations within thin low velocity surface layers below the recording site furthermore calculated crustal transfer functions for sh predict a peak over the range of 2 to 4 hz this type of site response can bias estimates of spectral parameters particularly corner or characteristic frequencies for simple sources such a bias can be reduced by filtering in the cepstral domain the effect of cepstral filtering on corner frequency determinations is generally less than 20 per cent and tends to decrease them particularly for larger events where the structurally induced spectral enhancement is at frequencies above the source related corner frequencies estimates of the seismic moment brune stress drop and fault radius for each event were calculated from sh displacement amplitude spectra the seismic moments range from 10 18 to 10 22 dyne cm the stress drops range from 0 008 to 16 bars the relationship between log stress drop and log moment is approximately linear with a slope of 1 up to a moment of 2 10 21 dyne cm but for higher moments the slope is not significantly different from zero fault radii range from 0 3 to 1 2 km there is a physical scatter in radius for any given moment up to a factor of 1 5 for moments less than 2 10 21 dyne cm there is no significant trend in the radius as a function of moment but for higher moments the radius increases with moment the main conclusion is that the stress drop is the dominant scaling factor for moments less than 10 21 dyne cm for higher moment the source dimension becomes the controlling factor

source mechanisms of usu volcano japan earthquakes and their tectonic implications abstract an intensive earthquake swarm and remarkable surface deformation due to dacitic doming have taken place at the usu volcano in southwestern hokkaido japan since august 1977 a major u shaped fault has formed in the summit crater and the amount of upheaval reached 180 m for 5 years in order to reveal the quantitative relation between this doming deformation and the associated earthquakes the mechanisms of the latter have been studied for this purpose broadband and wide dynamic range seismic observations were performed in a near field region of the usu volcano for the period from june 1979 to july 1980 long period seismometers and a digitally recording accelerometer system were used for relatively large earthquakes the data from the digital recording system permit very accurate calculations of ground displacements by employing the recursive filter method source parameters such as seismic moment average dislocation stress drop and fault dimensions for five earthquake families have been determined from a comparison of the observed ground displacements with synthetic ones synthetic displacements were computed using haskell s formulation for relatively deep earthquakes the discrete wavenumber dw method was used for relatively shallow earthquakes the stress drop varies widely among earthquakes in the same earthquake family the cumulative seismic deformation caused by the large earthquakes is almost consistent with the observed surface deformation it is suggested that the large earthquakes are caused by stick slip motions at the two sides of the u shaped fault

an ice rich flow origin for the banded terrain in the hellas basin mars the interior of hellas basin displays a complex landscape and a variety of geomorphological domains one of these domains the enigmatic banded terrain covers much of the northwestern part of the basin we use high resolution context camera and high resolution imaging science experiment digital terrain models to show that most of the complex viscous flowing behavior exhibited by the banded terrain is controlled by topography and flow like interactions between neighboring banded terrain furthermore the interior of the basin hosts several landforms suggestive of the presence of near surface ice which include polygonal patterns with elongated pits scalloped depressions isolated mounds and collapse structures we suggest that thermal contraction cracking and sublimation of near surface ice are responsible for the formation and the development of most of the ice related landforms documented in hellas the relatively pristine form lack of superposed craters and strong association with the banded terrain suggest an amazonian 3 ga age of formation for these landforms finally relatively high surface pressures above the triple point of water expected in hellas and summertime temperatures often exceeding the melting point of water ice suggest that the basin may have recorded relatively temperate climatic conditions compared to other places on mars therefore the potentially ice rich banded terrain may have deformed with lower viscosity and stresses compared to other locations on mars which may account for its unique morphology

train traffic as a powerful noise source for monitoring active faults with seismic interferometry laboratory experiments report that detectable seismic velocity changes should occur in the vicinity of fault zones prior to earthquakes however operating permanent active seismic sources to monitor natural faults at seismogenic depth is found to be nearly impossible to achieve we show that seismic noise generated by vehicle traffic and especially heavy freight trains can be turned into a powerful repetitive seismic source to continuously probe the earth s crust at a few kilometers depth results of an exploratory seismic experiment in southern california demonstrate that correlations of train generated seismic signals allow daily reconstruction of direct p body waves probing the san jacinto fault down to 4 km depth this new approach may facilitate monitoring most of the san andreas fault system using the railway and highway network of california

a idealized framework for the analysis of cohesive soils undergoing desiccation the authors wish to thank the discussers for their interest in the work on crack formation in clays during drying the model presented by the authors holds for soils with a high clay content in which desiccation cracks form while the soil is still saturated this was the case for the saint alban clay for which cracks appeared for a suction of about 23 kpa 18 hours after the soil surface was exposed to evaporation only the onset of cracking was modelled and crack depth is approximated with linear elastic fracture mechanics in mode i i e opening of the crack further crack propagation occurs with the ongoing evaporation leading eventually to the formation of secondary and even tertiary cracks if the soil is restrained in all directions furthermore these cracks depending on soil type may be initiated in an unsaturated soil hence we agree that the model must then also consider unsaturated soil mechanics owing to differential behaviour between a relatively dryer surface layer and soil at a higher moisture content with increasing depth secondary crack propagation may also be controlled in some cases by shear failure at the crack tip as stated by the discussers the cracking problem is complex and the subject received little attention so far

possible magma intrusion revealed by temporal gravity ground deformation and ground temperature observations at mount komagatake hokkaido during the 1996 1998 crisis summary mount komagatake 1131 m above sea level is a subduction related active volcano in hokkaido japan where two phreatic eruptions occurred in 1996 march and 1998 october after 54 years of dormancy we analyse four sessions of geodetic microgravity and ground temperature observations made over a two year period from november 1996 to may 1997 neither significant gravity nor significant elevation changes gps or levelling were observed from may 1997 to november 1997 we observed a slight subsidence 1 2 cm and contraction within 1 cm of the edifice a gravity increase 15 30 gal at the benchmarks inside the 2 km wide summit crater and a local temperature increase of 15 20 c at the summit crater from november 1997 to may 1998 we observed an edifice wide gravity increase of about 15 gal with no significant elevation change for benchmarks outside the summit crater besides this edifice scale variation we recorded a subsidence of about 5 6 cm and apparently no change of gravity inside the summit crater we inverted our data using models of increasing complexity elastic models are able to explain our deformation observations but they cannot explain either the gravity data or the temperature observations satisfactorily we introduced both an isothermal and a non isothermal porous medium filled with fluids to model deformation and gravity variations and we used a fissure model to invert the temperature anomaly our observations are consistent with a model of underground shallow water evaporation occurring as a result of heat rising from a hot and dense body density contrast of 200 kg m 3 of about 1011 kg at 4 5 km depth this interpretation suggests a possible intrusion of a magmatic body within the edifice

seismic energy releases from volcanoes seismic energy release during the precursory eruptive and declining stages of volcanic activities provides various information about the mechanisms of volcanic eruptions and the temporary developments of their activities hitherto the energy release patterns from precursory earthquake swarms were used to predict the eruption times especially of andesitic or dacitic volcanoes in this paper the discussion is expanded to quantify the total amount of seismic energy released at the threshold of volcanic eruptions with reference to the results observed at several volcanoes the results generally indicate that the cumulative seismic energy release from the precursory earthquake swarms exceed 1017 18ergs before eruptions at any andesitic or dacitic volvanoes this allows the seismic efficiency or the ratio of energy radiated seismically and the energy required for the volumetric expansion to be estimated by incorporating available deformation data with the seismic data the dependency of seismic efficiency on the type of volcanic activity i e non explosive outbreaks phreatic and magmatic eruptions dome formation etc was evaluated from observations at a few volcanoes that provided a variety of examples

global quieting of high frequency seismic noise due to covid 19 pandemic lockdown measures human activity causes vibrations that propagate into the ground as high frequency seismic waves measures to mitigate the coronavirus disease 2019 covid 19 pandemic caused widespread changes in human activity leading to a months long reduction in seismic noise of up to 50 the 2020 seismic noise quiet period is the longest and most prominent global anthropogenic seismic noise reduction on record although the reduction is strongest at surface seismometers in populated areas this seismic quiescence extends for many kilometers radially and hundreds of meters in depth this quiet period provides an opportunity to detect subtle signals from subsurface seismic sources that would have been concealed in noisier times and to benchmark sources of anthropogenic noise a strong correlation between seismic noise and independent measurements of human mobility suggests that seismology provides an absolute real time estimate of human activities

desiccation mechanism for formation of giant polygons on earth and intermediate sized polygons on mars results from a pre fracture model we present a pre fracture incrementally non linear elastic hydric model to constrain the models of formation of giant spacing of 20 300 m desiccation cracks on earth and possibly intermediate sized 80 to 350 m polygonal networks of cracks located in many impact craters on mars which have been interpreted to form by desiccation as opposed to thermal contraction el maarry et al 2010 the results of the model show that tensile stresses rise monotonically with desiccation however in soils with diffusivities below 10 4 m2 s it is not possible to generate high enough stresses to cause fracturing on the other hand intermediate values between 10 2 and 10 4 m2 s create optimum conditions for the formation of cracks at the time scales suggested for the formation of giant desiccation polygons on earth our model clearly shows that for typical diffusivity values of clayey soils with a considerable amount of smectites enough stress can build up to stimulate cracking of various spatial scales these results corroborate earlier assumptions that giant desiccation polygons on earth occur through lowering of the water table rather than surface evaporation extending the model to mars shows that soils would crack within similar diffusivity limits but in slightly longer periods of time owing to the lower gravity finally a model for formation of desiccation cracks on mars is presented that shows that two main conditions need to be fulfilled for desiccation cracks to occur under current martian climatic conditions namely that the thermal and soil diffusivity conditions 1 allow for the formation of an unsaturated zone with a considerable thickness while at the same time 2 limiting the growth of the permafrost downward which would disrupt the cracking process

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

observations of long period earthquakes accompanying hydraulic fracturing waveforms of most seismic events accompanying hydraulic fracturing have been reported to contain clear p and s waves and have fault plane solutions consistent with shear displacement across a fault this observation is surprising since classical hydraulic fracturing theory predicts the creation of a tensile opening of a cavity in response to fluid pressure very small long period events similar to long period earthquakes observed at volcanoes were found to occur during four hydraulic fracturing experiments carried out at fenton hill new mexico since the long period earthquakes occur in the same region as the shear type events it is concluded that the unusual character of the long period earthquake waveforms is due to a source effect and not a path effect the occurrence of long period earthquakes during hydraulic fracturing could indicate tensile fracturing many waveforms of these events are identical which implies that these events represent repeated activation of a given source a proposed source for these long period events is the sudden opening of a channel that connects two cracks filled with fluid at different pressures the sizes of the two cracks differ which causes two or more peaks to appear in the spectra each peak beingmore associated with one physical dimension of each crack from the frequencies at which spectral peaks occur crack lengths are estimated to be between 3 and 20m less

the nature of volcanic earthquake swarm preceding the 2000 flank eruption at usu volcano hokkaido japan summary the 2000 eruption of usu volcano hokkaido occurred on the northwestern flank of volcano on march 31 at 13 07 local time after about 4 days of intensive seismic activity we study the seismic process prior to the eruption using the routine earthquake catalogue of the japan meteorological agency jma and the digital seismograms of the short period station nbbt jma earthquakes began beneath the summit and southern slope of the volcano then seismic foci clustered along two linear zones intersecting to the south of the initial epicentral zone the majority of earthquakes occurred at depth within the range between 4 and 7 km the magnitude range of located earthquakes varied between 0 8 and 4 4 the earthquake epicentres did not reach the sites of the forthcoming eruption they stopped at a distance of about 1 3 km the eruption began during the ceasing of seismic activity a study of the nature of the swarm was performed for a sample of 303 earthquakes with a magnitude interval from 2 5 to 3 4 that were representative of the swarm visual analysis allowed separating the earthquakes into two groups 286 volcano tectonic vt earthquakes and 17 long period lp earthquakes the spectral analysis of s wave so f274 vt earthquakes in the frame of brune s model showed that the vt earthquakes may be separated into two groups as characterized by high stress drops hsd and low stress drops lsd the swarm began with hsd earthquakes the lsd and lp earthquakes were recorded about 30 40 hr later simultaneously with the beginning of deformation of volcanic edifice and accompanied the hsd earthquakes up to the beginning of eruption we attribute the hsd earthquakes to the probable product of magmatic thermal fracturing of host rocks the relatively long lsd ruptures may be attributed to the slips along the pre existing fractures during magma movement

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

field investigation of dried lakes in western united states as an analogue to desiccation fractures on mars potential desiccation polygons pdps tens to hundreds of meters in size have been observed in numerous regions on mars particularly in ancient 3 gyr old terrains of inferred paleolacustrine playa geologic setting and in association with hydrous minerals such as smectites therefore a better understanding of the conditions in which large desiccation polygons form could yield unique insight into the ancient climate on mars many dried lakebeds playas in western united states display large 50 m wide desiccation polygons which we consider to be analogues for pdps on mars therefore we have carried out fieldwork in seven of these dried lakes in san bernardino and the death valley national park regions complemented with laboratory and spectral analysis of collected samples our study shows that the investigated lacustrine playa sediments have a a soil matrix containing 40 75 clays and fine silt by volume where the clay minerals are dominated by illite muscovite followed by smectite b carbonaceous mineralogy with variable amounts of chloride and sulfate salts and significantly c roughly similar spectral signatures in the visible near infrared vis nir range we conclude that the development of large desiccation fractures is consistent with water table retreat in addition the comparison of the mineralogical to the spectral observations further suggests that remote sensing vis nir spectroscopy has its limitations for detailed characterization of lacustrine playa deposits finally our results imply that the widespread distribution of pdps on mars indicates global or regional climatic transitions from wet conditions to more arid ones making them important candidate sites for future in situ missions

relocation of swarm events in the june 1987 earthquake sequence from the lake aswan area in egypt we have examined the digital waveform data and relocated a number of events within the june 1987 earthquake swarm which occurred beneath the northern part of lake aswan 70 km southwest of the aswan high dam in egypt this swarm occurred between june 17th and 19th with a maximum magnitude event of m l 3 5 cross correlation between a chosen master and the analyzed events has been carried out on seismograms from stations of the aswan network the cross correlation demonstrates the presence of a difference in both the p wave t p and the s wave t s arrival times at each station in the network relative to the arrival times of the master event at the same stations t p ranges between 0 15 and 0 11 second while t s ranges between 0 17 and 0 11 second the primary interpretation is that the se time differences represent an error in the manually picking arrival times then t p and t s values for each event result from a change in the hypocentral parameters from those of the master event assuming the p and s wave velocity distribution remains constant during the swarm activity this interpretation enables us to determine the relative distribution of hypocenters with respect to the hypocentral location of the master event we present the results from a swarm of 9 events demonstrating they originate from a nearly unique location rather than the zone identified from the preliminary locations which used manually picked onset times

post eruptive volcanic dome evolution as revealed by deformation and microgravity observations at usu volcano hokkaido japan abstract usu volcano hokkaido japan is a dacitic volcano known for its high production rate of lava domes and crypto domes it is thus a good target to study processes of volcanic dome evolution upheaval and or relaxation we carried out repeated gps and microgravity surveys on the three most recent domes of mt usu 1910 meiji shinzan 1943 1945 showa shinzan and 1977 1982 usu shinzan the repeat period was 1 to 2 months and extended from october 1996 to june 1997 we also compare new data with results from former studies more than 20 years after the start of usu shinzan dome growth there is still subsidence at a maximum rate of about 7 to 8 cm year the reasons for this subsidence are discussed repeated gravity surveys revealed an increase of gravity on the domes about 60 10 microgal year for usu shinzan about 15 microgal at showa shinzan and 10 to 20 microgal for meiji shinzan this gravity increase exceeds that expected due to subsidence we discuss and interpret the excess gravity change in terms of a density increase in the edifice caused by a combination of processes contraction of the edifice water level change devesiculisation cooling and magma intrusion quantification of these processes at usu volcano may help to understand the processes of evolution at domes on other volcanoes such as merapi indonesia unzen japan or montserrat west indies

a 21 event 4 000 year history of surface ruptures in the anza seismic gap san jacinto fault and implications for long term earthquake production on a major plate boundary fault paleoseismic work completed at hog lake on the san jacinto fault sjf near anza california indicates that at least 21 surface ruptures have occurred in the anza seismic gap over the past 4 000 years the ages of the ruptures are constrained by 111 radiocarbon dates 97 of which fall in stratigraphic order the average recurrence interval for all ruptures for this period is about 185 105 years although some ruptures such as occurred in the april 1918 earthquake caused only minor displacement we rate the expression of each interpreted event in each of the twelve developed field exposures presented in this work by assigning numeric values for the presence of different criteria that indicate rupture to a paleo ground surface weakly expressed ruptures for example the deformation we interpret to be the result of the historical 1918 earthquake received low scores and are interpreted as smaller earthquakes from this analysis we infer that at least fifteen of the identified ruptures are indicative of large earthquakes similar to the penultimate earthquake inferred to be the m w 7 3 22 november 1800 earthquake the adjusted recurrence interval for large earthquakes lengthens to approximately 254 years comparison with the rupture history at the mystic lake paleoseismic site on the claremont strand indicates that it is plausible that several of the large ruptures identified at hog lake could have jumped the hemet step over at mystic lake and continued on the claremont strand or vice versa but most of the event ages do not match between the two sites indicating that most ruptures do not jump the step finally comparison with san andreas fault ruptures both to the north and south of its juncture with the sjf suggest that some northern sjf ruptures identified at mystic lake may correlate with events identified at wrightwood but that these northern ruptures have no match at hog lake and can not indicate rupture of the entire sjf onto the saf

morphology and evolution of the ejecta of hale crater in argyre basin mars results from high resolution mapping we use various data sets including images from the high resolution imaging science experiment camera hirise to examine the ejecta of the generally fresh looking hale crater that occurs in the rugged mountain terrain of nereidum montes in the northern rim materials of the argyre impact structure on mars our investigation reveals that the distal parts of the hale crater ejecta and other basin deposits behave like viscous flows which we attribute to the secondary flow of ejecta mixed with water ice rich basin materials consistent with water enrichment of the basin materials our mapping further reveals occasionally deformed surfaces including highly conspicuous features such as mounds and fractured plateaus that we interpret to be a result of periglacial modification subsequent including possibly present day to the transient localized melting and fluvial erosion caused by hale impact generated heating in particular our morphometric analysis of a well defined valley system west of hale crater suggests that it may have been formed through hydrologic glacial activity prior to the hale impact with additional modification resulting from the impact and subsequent geologic and hydrologic phenomena including glacial and periglacial activity

textural constraints on effusive silicic volcanism beyond the permeable foam model transitions between explosive and effusive phases of silicic volcanic eruptions have been related either to stratification of volatiles in the source magma body or to the loss of volatiles through the permeable host rock of the conduit one way to distinguish between these two models is to map and analyze the vesicular and glassy textures found in silicic lava flows in this paper we present textural observations and isotopic evidence from active and recent silicic lava flows which show that at least some vesiculation occurs during surface advance of extrusions after magma has reached the earth s surface this view is in contrast to the widely promoted permeable foam model which states that all volatiles escape during ascent of the magma and that all dense glassy material in lava flows forms from the collapse of pumiceous lava i e that silicic lavas emerge as highly inflated foam flows such interpretations which claim that silicic lavas are completely degassed upon extrusion and that all degassing must take place on the time scale of the eruption neglect several important pieces of evidence including the presence of obsidian in extremely small domes and of vesicular zones in the interiors of silicic flows the copious loss of volatiles through eruption plumes between eruptive phases and direct observations of surface vesiculation during growth of the mount st helens lava dome the permeable foam model also implies the unlikely requirement that explosive to effusive transitions be associated with an increase in eruption rate we present a more comprehensive model for the emplacement of silicic extrusions that allows for early gas loss during ascent as well as late stage vesiculation we then discuss how the redistribution of volatiles during surface flow can increase explosive hazards from silicic lavas days weeks or months after the lava emerges from the vent

energy partition in the 1982 eruption of el chichon volcano chiapas mexico abstract the 1982 eruption of el chichon volcano chiapas mexico has been extensively investigated from various standpoints including seismicity tephra geology atmospheric effects and tectonic structure in this paper the six largest of a series of explosions are isolated considering various sources of information then the seismic energy released by volcanic earthquakes and tremor is estimated using seismograms of low magnification in order to avoid saturation of seismic wave amplitudes the explosion kinetic energy is evaluated by two methods one by the initial velocity of the ejecta and the other by the air wave data recorded at a distance both the results are roughly coincident the thermal energy is classified into two components that transferred by volcanic ejecta and that consumed by convective clouds the thermal energy released by the explosions is very large compared with that of mechanical energy such as the seismic energy and explosion kinetic energy after the last major explosion of april 4 a type volcanic earthquakes swarmed till the end of april their occurrence rate decreased with time in an aftershock like sequence these earthquake swarms may have been due to post eruptive readjustment of the stress field within and near the volcano such seismic activity contrasts with other examples of similar major eruptions which were followed by growth of lava domes in the new craters after the paroxysmal eruptions the 1982 eruption of el chichon volcano has not been followed by the growth of a lava dome within the newly formed crater

giant desiccation fissures filled with calcareous eolian sand hermosa formation pennsylvanian southeastern utah abstract at two stratigraphic intervals within the upper member of the upper pennsylvanian hermosa formation calcareous eolian sand fills downward tapering fissures that are as much as 18 cm wide and 5 7 m deep fissure fillings define orthogonal polygons 10 m or more in diameter one of the host beds is primarily composed of subtidally deposited limestone the other is a thinly laminated nonmarine red siltstone both systems of fissure fillings are directly overlain and underlain by large scale cross stratified calcareous eolianites the limestone host bed contains chert pseudomorphs after gypsum compaction of host rocks contorted fissure fillings and caused doming of eolian strata over each fissure platy mineral grains in fissure fillings are aligned subparallel to bedding in the host rocks supporting the view that the fissures were passively filled rather than forcefully injected these ancient fissure systems are similar in scale and pattern to those that define giant desiccation polygons in numerous great basin playas the pennsylvanian fissures like their holocene counterparts probably formed when groundwater tables dropped from shallow levels within fine grained impermeable deposits into underlying aquifers greatly decreasing the extent of the capillary fringe our study of the fissures and host rocks supports the hypothesis that carbonate grains within the eolianites were deflated from uncemented marine sediments that were broadly exposed during regressive intervals

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

sequence of faulting and deformation during the 2000 eruptions of the usu volcano hokkaido japan interpretation and image analyses of aerial photographs abstract significant faulting and deformation of the ground surface has been rarely known during volcanic eruptions usu volcano hokkaido japan is a unique example of deformation due to felsic magma intrusion usu volcano has a history of such types of eruptions as phreatic pumice eruption plinian type pyroclastic flowing and lava doming since 1663 on march 31 2000 phreatomagmatic to phreatic eruptions took place after 23 years of dormancy in the western piedmont followed by explosions on the western flank of usu volcano they were associated with significant deformation including faulting and uplift the eruptions and deformation were continuing up to the end of may 2000 we identified the faulting using total nine sets of aerial photographs taken from before the eruption march 31 2000 to more than 1 year april 27 2001 after the end of the activity and traced deformation processes through image processing using aerial photographs we found that some of the new faults and the associated phreatic eruptions were related to old faults formed during the 1977 1981 eruptive episode the image processing has revealed that the surface deformation is coincident with the area of faulting forming small grabens and the phreatic explosion vents however the faulting and main explosive eruptions did not take place in the highest uplift area but along the margin this suggests that the faulting and explosive activities were affected by small feeder channels diverging from the main magma body which caused the highest uplift

a full scale field experiment 1978 1995 on the growth of permafrost by means of lake drainage western arctic coast a discussion of the method and some results on 13 august 1978 a lake on the western arctic coast was artificially drained in a multidisciplinary experiment on the growth of permafrost on the unfrozen bottom of the drained lake a bowl shaped talik unfrozen basin with a maximum depth of about 32 m underlay the lake bottom prior to drainage in the first winter after drainage downward freezing started on the exposed lake bottom and upward freezing from permafrost beneath the talik after drainage the soft lake bottom sediments hardened from water loss and freeze thaw consolidation gradual thinning of the active layer at many sites was accompanied by ground uplift and the growth of aggradational ice downward and upward freezing has resulted in solute rejection freezing point depressions pore water expulsion from the freezing of the saturated lake bottom sands and convective heat transfer from groundwater flow in an open hydrologie system the increasingly saline intrapermafrost groundwater flowing at an increasingly negative temperature be

fracturing associated with the 1977 1978 eruption of usu volcano north japan as revealed by geophysical measurements abstract none of the ground temperature measurements inside the somma caldera of usu volcano in southwestern hokkaido japan show patterns that correlate with the development of surface faults and the hypocenter distribution of earthquake swarms observed during the 1977 1978 eruptions audiomagnetotelluric a m t soundings on the surface of the somma caldera display well defined high resistivity zones h r z within the low resistivity edifice h r z are explained as being due to rising dry steam and low resistivity zones are attributed to ionized water in the volcanic edifice inversion of data shows that elongated h r z have a shallow roof and are some hundred meters wide steam rising along narrow vertical fractures generates widely distributed vapor dominated geothermal systems because rising steam condenses near the surface the condensed steam creates a water filled zone which inhibits the free escape of succeeding steam distribution of elongated h r z correlates well with the high ground temperature zones a self potential survey reveals a positive anomaly developed over the usu edifice about 350 mv in magnitude electrokinetic coupling effect due to intensive hydrothermal convection is a probable interpretation of the anomaly because the high potential zone is closely related to a high ground temperature zone hydraulic fracturing of the upper crust at the time of eruption allowed release of elastic strain energy due to magma pressure at depths with the spectacular consequence that one side of the major fracture was uplifted about 180 m the geometry of such a process may be drawn from seismological results the roof of the edifice is pushed up by expanding magma accompanying intensive seismic activities we suggest that earthquake free zones are proof of magma filled fractures and that eruption took place when one of these fractures opened to the surface

geology and mineralogy of the auki crater tyrrhena terra mars a possible post impact induced hydrothermal system abstract a variety of hydrothermal environments have been documented in terrestrial impact structures due to both past water interactions and meteoritic bombardment on the surface of mars several authors have predicted various scenarios that include the formation of hydrothermal systems geological and mineralogical evidence of past hydrothermal activity have only recently been found on mars here we present a geological and mineralogical study of the auki crater using the spectral and visible imagery data acquired by the crism compact reconnaissance imaging spectrometer for mars ctx context camera and hirise high resolution imaging science experiment instruments on board the nasa mro mission the auki crater is a complex crater that is 38 km in diameter located in tyrrhena terra 96 8 e and 15 7 s and shows a correlation between its mineralogy and morphology the presence of minerals such as smectite silica zeolite serpentine carbonate and chlorite associated with morphological structures such as mounds polygonal terrains fractures and veins suggests that the auki crater may have hosted a post impact induced hydrothermal system although the distribution of hydrated minerals in and around the central uplift and the stratigraphic relationships of some morphological units could also be explained by the excavation and exhumation of carbonate rich bedrock units as a consequence of crater formation we favor the hypothesis of impact induced hydrothermal circulation within fractures and subsequent mineral deposition the hydrothermal system could have been active for a relatively long period of time after the impact thus producing a potential transient habitable environment

periglacial landforms at the phoenix landing site and the northern plains of mars 1 we examine potentially periglacial landforms in mars orbiter camera moc and high resolution imaging science experiment hirise images at the phoenix landing site and compare them with numerical models of permafrost processes to better understand the origin nature and history of the permafrost and the surface of the northern plains of mars small scale 3 6 m polygonal patterned ground is ubiquitous throughout the phoenix landing site and northern plains larger scale 20 25 m polygonal patterns and regularly spaced 20 35 m rubble piles localized collections of rocks and boulders are also common rubble piles were previously identified as basketball terrain in moc images the small polygon networks exhibit well developed and relatively undegraded morphology and they overlay all other landforms comparison of the small polygons with a numerical model shows that their size is consistent with a thermal contraction origin on current day mars and are likely active in addition the observed polygon size is consistent with a subsurface rheology of ice cemented soil on depth scales of about 10 m the size and morphology of the larger polygonal patterns and rubble piles indicate a past episode of polygon formation and rock sorting in thermal contraction polygons while the ice table was about twice as deep as it is presently the pervasive nature of small and large polygons and the extensive sorting of surface rocks indicates that widespread overturning of the surface layer to depths of many meters has occurred in the recent geologic past this periglacial reworking has had a significant influence on the landscape at the phoenix landing site and over the martian northern plains

shear wave imaging from traffic noise using seismic interferometry by cross coherence we apply the cross coherence method to the seismic interferometry of traffic noise which originates from roads and railways to retrieve both body waves and surface waves our preferred algorithm in the presence of highly variable and strong additive random noise uses cross coherence which uses normalization by the spectral amplitude of each of the traces rather than crosscorrelation or deconvolution this normalization suppresses the influence ofadditive noise and overcomes problems resulting from amplitudevariations among input traces by using only the phase information and ignoring amplitude information the method effectively removes the source signature from the extracted response and yields a stable structural reconstruction even in the presence of strong noise this algorithm is particularly effective where the relative amplitude among the original traces is highly variable from trace to trace we use the extracted reflected shear waves from the traffic noise data to construct a stackedandmigratedimage andweusetheextractedsurfacewaves love waves to estimate the shear velocity as a function of depth this profile agrees well with the interval velocity obtained from the normal moveout of the reflected shear waves constructed by seismic interferometry these results are useful in a wide range of situations applicable to both geophysics and civil engineering

modelling of curling in desiccating clay this paper investigates the significant curling that occurs when thin soil layers undergo desiccation curling deformations in the form of 1 lifting off from the edges generating a concave surf

conditions for detection of ground deformation induced by conduit flow and evolution 1 at mature andesitic volcanoes magma can reach the surface through the same path for several eruptions thus forming a volcanic conduit because of degassing cooling and crystallization magma viscosity increase in the upper part of the conduit may induce the formation of a viscous plug we conducted numerical simulations to quantify the deformation field caused by this plug emplacement and evolution stress continuity between newtonian magma flow and elastic crust is considered plug emplacement causes a ground inflation correlated to a decrease of the magma discharge rate a parametric study shows that surface displacements depend on three dimensionless numbers the conduit aspect ratio radius length the length ratio between the plug and the conduit and the viscosity contrast between the plug and the magma column larger displacements are obtained for high viscosity plugs emplaced in large aspect ratio conduits we find that only tiltmeters or gps located close to the vent a few hundred meters might record the plug emplacement at immediate proximity of the vent plug emplacement might even dominate the deformation signal over dome growth or magma reservoir pressurization effects for given plug thicknesses and viscosity profiles our model explains well the amplitude of tilt variations from 1 to 25 rad measured at montserrat and mt st helens we also demonstrate that at montserrat even if most of the tilt signal is due to shear stress induced by magma flow pressurization beneath the plug accounts for 20 of the signal

magma prospecting in usu volcano hokkaido japan using magnetotelluric soundings abstract we carried out magnetotelluric mt soundings across usu volcano hokkaido japan which has been active since 1663 the objective was to image an intrusion expected below the formation of 180m high cryptodomes formed during the 1977 78 eruption a ne sw two dimensional resistivity model has been obtained from the inversion in the frequency range from 0 01 to 10 000 hz the major features of the resistivity section are as follows 1 a 50 m thick surficial resistive 1000 10 000 m layer corresponding to the lava layer 2 a relatively conductive 10 1000 m layer from the surface to 200 m depth corresponding to quaternary sedimentary and volcanic rocks 3 beneath the quaternary formations a thick 2 4 km conductive 1 500 m layer of altered tertiary volcanics distributed widely in the volcanic edifice 4 a resistive block 500 1 000 m in the tertiary layer from 200 to 400 m in depth beneath the summit crater forming a striking contrast to the rest of the conductive tertiary layer and probably indicating a cooling intrusion at shallow depth 5 pre tertiary formations consisting of a high resistivity 1000 10 000 m layer overlying a conductive layer with the top of the pre tertiary becoming shallow to the northeast and 6 no deep conductive anomalies corresponding to a magma chamber inferred from petrological studies

fundamentals of desiccation cracking of fine grained soils experimental characterisation and mechanisms identification this paper presents the results of a comprehensive experimental study of the desiccation of fine grained soils air drying of initially saturated soil slabs in controlled conditions is investigated by performing three kinds of tests free desiccation tests constrained desiccation tests prevented shrinkage and crack pattern tests strains suction water con tent and crack geometry are investigated results reveal that unconstrained drying exhibits two stages a domain with large mostly irrecoverable deformations and degree of saturation close to 100 followed by a domain with lower defor mations at a decreasing degree of saturation homogeneous soil macroscopic cracking is possible only in the presence of boundary constraints and or moisture gradients inducing the build up of tensile stresses results also show that for the initially saturated remoulded soils tested here in the whole sample and near a crack initiation point the degree of satura tion remains very close to 100 until cracking while cracking onset the air entry suction and the shrinkage limit are close to each other cavitation nuclei and the formation of an irregular drying front at cracking initiation are commented upon in light of this observation finally results suggest that the crack pattern geometry is the result of energy redistribu tion a quantification of the process is proposed resume cet article presente les resultats d une etude experimentale complete de la dessiccation de sols fins le sechage de sols initialement satures est etudiedans des conditions controlees et atemperature ambiante trois types d essais ont eteeffectues essais de dessiccation libre essais de dessiccation avec contraintes le retrait est empechedans une direc tion et essais de plans de fissures les deformations la succion la teneur en eau et la geometrie des fissures ont eteinves tiguees les resultats demontrent que le sechage sans contrainte presente deux etapes un domaine durant lequel les deformations sont grandes et irreversibles et le degrede saturation reste pres de 100 suivi d un domaine durant lequel les deformations sont plus faibles et le degrede saturation diminue pour un sol homogene des fissures macroscopiques apparaissent seulement lorsqu il y a des contraintes aux frontieres et ou des gradients d humidite ce qui induit des contraintes en tension les resultats montrent aussi que pour les silts et argiles remanies initialement satures utilises dans cette etude le degrede saturation reste tres pres de 100 jusqu ala fissuration de plus la fissuration l entree d air et la limite de retrait sont proches les unes des autres suite a ces observations l existence de germes de cavitation et la forma tion d un front de sechage irregulier lors de l initiation des fissures sont discutees finalement les resultats suggerent que la geometrie des fissures resulte d une redistribution de l energie a travers le corps une quantification du processus est proposee mots cles dessiccation initiation de fissure succion succion a l entree d air geometrie des fissures

inter eruptive volcanism at usu volcano micro earthquakes and dome subsidence abstract post eruptive crustal activity after the 2000 eruption of usu volcano was investigated by seismic and geodetic field observations remarkable features of the magmatic eruptions that occur almost every 30 years include lava dome formation and strong precursory earthquakes on the other hand rapid dome subsidence was observed by electronic distance meter edm measurement after the 1977 1982 summit eruption since the 2000 eruption seismic activity at a shallow part under the summit crater has remained at a high level relative to that after the 1977 1982 eruption although eruption occurred at the western foot of the volcano during the 2000 eruption to reveal the shallow crustal activity in the inter eruptive period around the summit area seismicity and crustal deformation have been investigated since 2006 dense temporary seismic observations and hypocenter relocation analysis using a three dimensional velocity structure model revealed that the focal area is localized along the u shaped fault that developed in the dome forming stage of the 1977 1982 eruption three major focal clusters are distributed on the southwestern side of usu shinzan cryptodome which was built up during the 1977 1982 eruption for the seven major events with magnitudes larger than 1 the focal mechanism was a large dip slip component which suggests the subsidence of usu shinzan cryptodome interferomatetric satellite aperture radar insar image analysis and repeated gps measurements revealed subsidence of the summit dome which is almost centered at the usu shinzan cryptodome the area of rapid deformation is restricted to a small area around the summit crater the estimated rate of dome subsidence relative to the crater floor is about 3 cm year these results strongly suggest that subsidence of usu shinzan is associated with the small earthquakes along the u shaped fault that surrounds the cryptodome according to prior seismic and geodetic studies it is thought that most of the magma rising under the summit crater during the 2000 eruption stopped around a depth of 2 km below sea level which is sufficiently deep relative to the focal area of the present seismicity a part of the magma intruded under the western foot and contributed to the 2000 eruption we conclude that the 2000 eruption scarcely affected the shallow crustal activity under the summit crater and that usu shinzan cryptodome is continuing to subside just as it was before the 2000 eruption the shallow volcanic earthquakes that began increasing from 1995 are closely related to the successive subsidence of the summit domes temporal change in fumarole temperature suggests a relationship between the shallow earthquakes and cooling of the magma that intruded under usu shinzan during the 1977 1982 eruption

a tensile shear crack model for the mechanism of volcanic earthquakes abstract temporary seismic observations were carried out for about 1 month at miyakejima island on the izu bonin arc after an eruption on october 3 1983 more than 3000 seismic events were observed and they are classified into 4 different categories short period earthquakes long period earthquakes isolated tremors and continuous tremors two active source regions of the short period earthquakes were located along the old caldera rim of the miyakejima volcano one region was very close to the eruptive fissures another was about 1 2 km northwest of the fissures almost all the earthquakes in the former region showed dilatant first motions of p waves at all the stations in the island on the other hand almost all events in the latter region showed compressive first motions of p waves at all the stations the first motions of p waves for these earthquakes cannot be explained by the quadrant type pattern due to a double couple force system nucleation of a tensile crack coupled with a shear crack a tensile shear crack model is proposed as a source mechanism of the short period earthquakes moment tensor elements of tensile and shear cracks have been determined by the least squares method using observed p and s wave data results suggest that tensile cracking opening or closing is dominant for generating those earthquakes in comparison with shear cracking the strikes of the tensile cracks for the earthquakes are shown to be nearly parallel to the strike of the fissures the earthquakes that occurred in the northwestern region of the fissures are considered to be generated by a sudden opening of tensile shear cracks due to the excess pressure of intrusive magma in contrast the earthquakes occurring beneath the fissures are probably generated by a sudden closing of tensile shear cracks and this suggests that the magmatic pressure under the fissures rapidly decreased after the eruption moment tensor analysis of the tensile shear crack model in this study demonstrates the non double couple source mechanism for volcanic earthquakes related to magmatic activity

analogue modeling of instabilities in crater lake hydrothermal systems 1 we carried out analogue experiments on two phase boiling systems using a porous vertical cylinder saturated with water the base of the cylinder was heated and the top was cooled as in a natural hydrothermal system previous work had shown that once the two phase zone reached a certain level thermal instabilities would develop we made measurements of the acoustic energy related to boiling and we found that high levels of acoustic noise were associated with the part of the cycle in which there was upward water movement we repeated our experiments with a cooling water tank at the top of the system representing a crater lake this showed that periodic thermal instabilities still developed in this situation we then compared our analogue measurements to two natural systems known to exhibit periodic behavior there is good agreement between the thermal and acoustic cycling seen in our model and the observations made at inferno crater lake in the waimangu geothermal area new zealand whose level cycles by nearly 10 m with a typical period of 38 days particularly notable is how in both systems high levels of acoustic noise are associated with rising water level the much larger ruapehu crater lake also in new zealand cycled with a period of several months to a year for over a decade prior to the 1995 eruption strong acoustic and seismic energy usually occurred just before the lake temperature started to rise this suggests a slightly different model in which the increasing two phase flow zone triggers more general convection once it reaches the base of the lake

body and surface wave reconstruction from seismic noise correlations between arrays at piton de la fournaise volcano body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring here we extract body and surface waves that propagate in piton de la fournaise volcano on la reunion island using ambient noise cross correlation and array processing techniques ambient noise was continuously recorded at three dense arrays each comprising 49 geophones to identify and enhance the green s function from the ambient noise correlation we apply a double beamforming dbf technique between the array pairs the dbf allows us to separate surface and body waves direct and reflected waves and multipathing waves based on their azimuths and slownesses we successfully extract body waves between all the combinations of arrays including the wave that propagates through the active magmatic system of the volcano additionally we identify the effects of uneven noise source distribution and interpret the surface wave reflections

small scale polygonal features on mars seasonal thermal contraction cracks in permafrost a time dependent viscoelastic model of thermal stress in martian ice rich permafrost is developed to test the hypothesis that small scale polygonal features observed from orbit and by the viking lander 2 are the result of thermal contraction cracking as commonly occurs in terrestrial permafrost results indicate that significant tensile stress occurs in martian ice rich permafrost as a result of seasonal cycles in the ground temperature using conservative rheological parameters appropriate for ice at low temperatures tensile stresses poleward of about 20 to 30 latitude easily exceed the tensile strength assumed to be 2 to 3 mpa and fractures should readily form in the equatorial regions special conditions may allow tensile stresses to approach the tensile strength these results support a thermal contraction origin of observed small scale polygonal features and emphasize the utility of these features as valuable morphological indicators of ground ice

meter scale thermal contraction crack polygons on the nucleus of comet 67p churyumov gerasimenko we report on the detection and characterization of more than 6300 polygons on the surface of the nucleus of comet 67p churyumov gerasimenko using images acquired by the osiris camera onboard rosetta between august 2014 and march 2015 they are found in consolidated terrains and grouped in localized networks they are present at all latitudes from north to south and longitudes head neck and body sometimes on pit walls or following lineaments about 1 5 of the observed surface is covered by polygons polygons have an homogeneous size across the nucleus with 90 of them in the size range 1 5 m and a mean size of 3 0 1 4 m they show different morphologies depending on the width and depth of their trough they are found in networks with 3 or 4 crack intersection nodes the polygons observed on 67p are consistent with thermal contraction crack polygons formed by the diurnal or seasonal temperature variations in a hard mpa and consolidated sintered layer of water ice located a few centimeters below the surface our thermal analysis shows an evolution of thermal contraction crack polygons according to the local thermal environment with more evolved polygons i e deeper and larger troughs where the temperature and the diurnal and seasonal temperature range are the highest thermal contraction crack polygons are young surface morphologies that probably formed after the injection of 67p in the inner solar system typically 100 000 years ago and could be as young as a few orbital periods following the decreasing of its perihelion distance in 1959 from 2 7 to 1 3 a u meter scale thermal contraction crack polygons should be common features on the nucleus of jupiter family comets

high latitude patterned grounds on mars classification distribution and climatic control patterned grounds such as polygonal features and slope stripes are the signature of the presence of ground ice and of temperature variations in cold regions on earth identifying similar features on mars is important to understand its past climate as well as the ground ice distribution in this study young patterned grounds are classed and mapped from the systematical analysis of mars observer camera high resolution images these features are located poleward of 55 latitude which fits the distribution of ground ice found by the neutron spectrometer onboard mars odyssey thermal contraction due to seasonal temperature variations is the predominant process of formation of polygons formed by cracks which sizes vary from 15 to 300 m the small 40 m widespread polygons are very recent and degraded by the desiccation of ground ice from the cracks which enhances the effect of ice sublimation the large polygons 50 to 300 m located only around the south co2 polar cap indicate the presence of ground ice and thus outline the limit of the co2 ice cap they could be due to the blanketing of water ice deposits by the advances and retreats of the residual co2 ice cap during the last thousand years large 50 250 m and homogeneous polygons similar to ice wedge polygons hillslope stripes and solifluction lobes may indicate that specific environments such as crater floors and hillslopes could have been submitted to freeze thaw cycles possibly related to higher summer temperatures in periods of obliquity higher than 35 these interpretations must be strengthened by higher resolution images such as those of the hirise mission of the mars reconnaissance orbiter because locations with past seasonal thaw could be of major interest as potential landing sites for the phoenix mission

the 1980 pressure response and flank failure of mount st helens usa inferred from seismic scaling exponents the cataclysmic 18 may 1980 eruption at mount st helens was preceded by intense seismic activity marking the mechanical response of the volcanic edifice to interior pressurisation this seismicity is analysed to yield the temporal change in the seismic scaling exponent d inferred from the seismic b value that in turn is related to the seismic moment of an earthquake time evolution of d preceding the eruption onset reveals 1 a major decrease in d occurring over only a few days at the end of march 2 a steady but stepped decrease in d steps 5 10 days occurring from the end of march to early may 3 a sharp decrease in d in early may and 4 steady low values of d occurring 2 3 days before the eruption onset this response is interpreted as major ruptures formed at the end of march arresting and participating in but not triggering the ultimate failure of the flank rather the rate of interior fracturing slowed in the 2 months preceding the 18 may 1980 major blast and the triggering of failure is consistent with interior gas overpressurisation the occurrence of two swarms of low frequency seismic events and the high values of the harmonic tremor indicate the action of interior pressurisation on a cycle of 20 25 days solutions are applied to represent the harmonic interior pressurisation of the edifice by gas exsolving from the volcano core the transient radial migration of overpressured gas may reduce the apparent strength of the edifice and ultimately trigger failure of the flank importantly this mechanism is capable of triggering flank failure both after multiple core pressurisation cycles have been sustained and as core pressures are low and diminishing and may be a minimum these twin attributes are both apparent in the seismic record for mount st helens used as a proxy for the unrecorded timing and magnitude of gas pressurisation at the volcano core d 2004 elsevier b v all rights reserved

the western qaidam basin as a potential martian environmental analogue an overview the early martian environment is interpreted as warmer and wetter before a significant change in its global climatic conditions irreversibly led to the current hyper arid environments this transition is one of the most intriguing processes of martian history the extreme climatic change is preserved in the salt deposits desiccated landscapes and geomorphological structures that were shaped by the evaporation of water however until a manned journey to mars is feasible many martian materials morphological structures and much of its evolutionary history will continue to be poorly understood in this regard searching and investigating martian analogues is still meaningful to find an earth environment with a whole set of martian structures distributed at a scale comparable to mars is even more important to test landing crafts and provide optimized working parameters for rovers the western qaidam basin in north tibetan plateau is such a martian analogue the area harbors one of the most extreme hyper arid environments on earth and contains a series of ancient lakes that evaporated at different evolutionary stages during the rise of the tibetan plateau large quantities of salts and geomorphological features formed during the transition of warmer and wet to colder and dry conditions provide unique references to study the modern martian surface and interpret the orbital data we present numerous similarities and results of investigations that suggest the qaidam basin as a potential analogue to study modern geomorphic processes on mars and suggest that this is an essential site to test future mars sample return missions

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

precursory seismicity of the 1994 eruption of popocatepetl volcano central mexico popocatepetl volcano is located in the central mexican volcanic belt within a densely populated region inhabited by over 20 million people the eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions including plinian events after nearly 70 years of quiescence popocatepetl reawakened in december 21 1994 the eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth and destruction episodes similar to events that have apparently been typical for popocatepetl since the fourteenth century in this regime the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence in this paper we analyze five years of volcano tectonic seismicity preceding the initial eruption of the current episode the evolution of the v t seismicity shows four distinct stages which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence the thermal effects of a magma intrusion at depth the fracturing related to the slow development of magma related fluid pathways the concentration of stress causing a protracted acceleration of this process and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of v t seismic energy release a hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption the total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes limit that was reached by popocatepetl before the eruption

analysis of polygonal cracking patterns in chloride bearing terrains on mars indicators of ancient playa settings the ancient southern highlands on mars 3 5 gyr old contain 600 regions that display spectral evidence in the infrared for the presence of chloride bearing materials many of these locations were previously reported to display polygonal cracking patterns we studied more than 80 of the chloride bearing terrains using high resolution 0 25 0 5 m pixel images as well as near infrared spectral data to characterize the surface textures and the associated cracking patterns and mineralogies our study indicates that 75 of the studied locations display polygonal cracks that resemble desiccation cracks while some resemble salt expansion thrust polygons furthermore we detect spectrally the presence of smectites in association with 30 of the studied fractured terrains we note that smectites are a special class of swelling clay minerals that can induce formation of large desiccation cracks as such we suggest that the cracking patterns are indicative of the presence of smectite phyllosilicates even in the absence of spectral confirmation our results suggest that many chloride bearing terrains have a lacustrine origin and a geologic setting similar to playas on earth such locations would have contained ephemeral lakes that may have undergone repeated cycles of desiccation and recharging by a near surface fluctuating water table in order to account for the salt phyllosilicates associations these results have notable implications for the ancient hydrology of mars we propose that the morphologies and sizes of the polygonal cracks can be used as paleoenvironmental as well as lithological indicators that could be helpful in planning future missions

hydrological and geochemical change related to volcanic activity of usu volcano japan abstract mt usu is a stratovolcano located on the southern side of the toya caldera in hokkaido japan in historical times it emitted dacitic products associated to remarkable crustal deformations usu volcano erupted on march 31st 2000 after 23 yr of dormancy and this eruption was the fourth in the 20th century secular variations in water levels temperature and chemical compositions of thermal water have been observed around usu volcano the water levels decreased since october 1999 6 months prior to the eruption the decrease in water levels is a precursory change and is probably due to leakage of thermal water from the shallow aquifer hosting it no variations in temperature and chemical composition of thermal water were evident prior to the eruption however in a few wells the temperature of the thermal water increased by up to 15 c with respect to the pre eruptive values moreover the concentration of some solutes na k cl and so4 became higher after the eruption these thermal and chemical changes are ascribable to increased input of a deep hydrothermal liquid into the shallow groundwater aquifer

possible precipitation of ice at low latitudes of mars during periods of high obliquity most of the old cratered highlands of mars are dissected by branching river valleys that appear to have been cut by running water1 2 yet liquid water is unstable everywhere on the martian surface in the equatorial region where most of the valleys are observed even ice is unstable3 4 it has been suggested therefore that mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water5 here we suggest instead that during periods of very high obliquities ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards at low latitudes the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed the mechanism is efficient only at the very high obliquities that occurred before formation of tharsis very early in the planet s history but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet s history partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system

macropolygon morphology development and classification on north panamint and eureka playas death valley national park ca abstract panamint and eureka playas both located within death valley national park exhibit a host of surficial features including fissures pits mounds and plant covered ridges representing topographic highs and lows that vary up to 2 m of relief from the playa surface aerial photographs reveal that these linear strands often converge to form polygons ranging in length from several meters to nearly a kilometer these features stand out in generally dark contrast to the brighter intervening expanse of flat plant free desiccated mud of the typical playa surface ground truth mapping of playa features with differential gps global positioning system was conducted in 1999 north panamint valley and 2002 eureka valley high resolution digital maps reveal that both playas possess macropolygons of similar scale and geometry and that fissures may be categorized into one of two genetic groups 1 shore parallel or playa interior desiccation and shrinkage and 2 tectonic induced cracks early investigations of these features in eureka valley concluded that their origin may have been related to agricultural activity by paleo indian communities although human artifacts are abundant at each locale there is no evidence to support the inference that surface features reported on eureka playa are anthropogenic in origin our assumptions into the genesis of polygons on playas is based on our fortuitous experience of witnessing a fissure in the process of formation on panamint playa after a flash flood may 1999 our observations revealed a paradox that saturation of the upper playa crusts contributes to the establishment of some desiccation features follow up visits to the same feature over 2 yrs time are a foundation for insight into the evolution and possible longevity of these features

seismological significance of the 1977 1978 eruptions and the magma intrusion process of usu volcano hokkaido abstract an earthquake swarm and the major pumice eruptions in august 1977 which followed marked the start of the dacitic doming activity of usu volcano in southwestern hokkaido japan the sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data the distribution of the abundant hypocenters shows clearly an earthquake free zone beneath the summit crater the hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations considered due to magma intrusion into this earthquake free zone the earthquake mechanism solutions are mostly of dip slip type and are interpreted in terms of the doming deformations the existence of earthquake families earthquakes with similar waveforms is the main cause of the peculiar occurrence of earthquakes in space time and magnitude the concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm and the observed episodic deformations

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

source parameters and scaling relationships of small earthquakes in the northeastern caribbean abstract the seismic moments and stress drops of 23 earthquakes 1 1 m 2 4 that occurred during an earthquake swarm in the virgin islands were determined from the analysis of their p waveforms the data consist of digitally recorded seismograms collected by a short period seismic network operating in the northeastern caribbean the events of the swarm are particularly useful for comparing the relative stress drops of small earthquakes because their source to receiver paths and focal mechanisms are very similar the static stress drops calculated for these earthquakes varied from about 0 2 to 2 bars the data clearly illustrate that the static and dynamic stress drops of these earthquakes generally increased with the size moment of the events the fault radii for these shocks increased with seismic moment but only by a factor of 2 for a 100 fold increase in seismic moment the velocity waveforms of the larger events were systematically more impulsive than those of the smaller earthquakes these observations imply that for this set of earthquakes the final fault radius is a function of the stress drop that occurs during the rupture process

a new terrestrial analogue site for mars research the qaidam basin tibetan plateau nw china abstract remote sensing observations and rover missions have documented the presence of playas salts and wind erosion landforms of lacustrine sediments on mars all of these observations suggest mars was aqueous in its early history however abundant questions remain how wet was the environment what were the properties of the liquids and the possibility of ancient habitability and what kinds of geological processes shaped the present landforms to explore these unknowns analogue studies can play a key role in this contribution we introduce the qaidam basin tibetan plateau northwestern china as a new and unique analogue site for studying the past aqueous and present arid environments of mars the qaidam basin the highest and one of the largest and driest deserts on earth is located in a dry cold and high uv environment similar to the surface of mars we demonstrate a variety of landforms and also their counterparts on mars which include aeolian dunes and yardangs polygons gullies valleys and fluvial fans in the qaidam basin various environmental regimes for the formation of linear and asymmetric barchans have been described saline lakes and playas representing different stages of lake evolution in arid environment are also present in the qaidam basin and provide promising cases for studying the habitability in mars like environments results for microorganism isolation suggest that halophiles are the most important fraction in the hypersaline sediments and this may shed light on studying present martian habitability moreover the remote but ready accessibility of the qaidam basin make it a potential site for engineering testing in regards to future martin exploration missions we propose that the variety of exogenic and endogenic geomorphic types lacustrine sediments evaporite mineral assemblages and mars like extreme environments collectively point to the qaidam basin as an optimal

potential desiccation cracks on mars a synthesis from modeling analogue field studies and global observations potential desiccation polygons pdps are polygonal surface patterns that are a common feature in noachian to hesperian aged phyllosilicate and chloride bearing terrains and have been observed with size scales that range from cm wide by current rovers to 10s of meters wide the global distribution of pdps shows that they share certain traits in terms of morphology and geologic setting that can aid identification and distinction from fracturing patterns caused by other processes they are mostly associated with sedimentary deposits that display spectral evidence for the presence of fe mg smectites al rich smectites or less commonly kaolinites carbonates and sulfates in addition pdps may indicate paleolacustrine environments which are of high interest for planetary exploration and their presence implies that the fractured units are rich in smectite minerals that may have been deposited in a standing body of water a collective synthesis with new data particularly from the hirise camera suggests that desiccation cracks may be more common on the surface of mars than previously thought a review of terrestrial research on desiccation processes with emphasis on the theoretical background field studies and modeling constraints is presented here as well and shown to be consistent with and relevant to certain polygonal patterns on mars

source parameters of seismic events at heinrich robert mine ruhr basin federal republic of germany evidence for nondouble couple events abstract a three component digital seismic station is in operation at heinrich robert coal mine in the ruhr basin at a depth of 890 m a cluster of seismic events occurred at the beginning of 1987 at a distance of about 5 km from the station and continued in 1988 source parameters of 46 tremors selected from the cluster with local magnitude from 1 2 to 2 3 are studied the ratio of p wave to s wave corner frequency is variable implying its dependence on the angle of observation and in turn the variability of focal mechanism with time the scaling relations indicate that characteristic tremors with a fault length of about 200 m are possibly generated in the area but the evidence is not conclusive the seismic energy for a given seismic moment can vary by a factor of 20 and the ratio of s wave to p wave energy ranges from 1 5 to 30 stress release estimates show low values not exceeding a few bars typical for tremors induced by mining a comparison of the apparent stress with the static stress drop divides the selected tremors into high and low apparent stress events the latter events are characterized by high p wave energy and almost constant and large ratio of p wave to s wave corner frequency which differs from the lower ratios of other events implying similar focal mechanism these high p wave energy tremors are the most likely candidates for nondouble couple events

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

impact crater lakes on mars the robotic search for life on mars centers on identifying accessible environments where the biological catalyst water has existed the formation of large impact craters on mars 65 km diameter may have resulted in the creation of ice covered impact crater lakes which would not freeze for thousands of years even under present climatic conditions water could be supplied from deep confined aquifers penetrated by the impact craters without the need for surface melt water freezing of the lakes is postponed owing to heat from impact generated melt bearing deposits from impact related uplift of hotter rocks from depth and from the latent heat of freezing of a deep crater lake abundant morphologic evidence for ancient crater lakes has not been found in viking images except for craters associated with outflow channels however ice covered crater lakes could have formed and further searches for evidence of these lakes are warranted the lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from mars

clastic polygonal networks around lyot crater mars possible formation mechanisms from morphometric analysis polygonal networks of patterned ground are a common feature in cold climate environments they can form through the thermal contraction of ice cemented sediment i e formed from fractures or the freezing and thawing of ground ice i e formed by patterns of clasts or ground deformation the characteristics of these landforms provide information about environmental conditions analogous polygonal forms have been observed on mars leading to inferences about environmental conditions we have identified clastic polygonal features located around lyot crater mars 50 n 30 e these polygons are unusually large 100 m diameter compared to terrestrial clastic polygons and contain very large clasts some of which are up to 15 metres in diameter the polygons are distributed in a wide arc around the eastern side of lyot crater at a consistent distance from the crater rim using high resolution imaging data we digi tised these features to extract morphological information these data are compared to existing terrestrial and martian polygon data to look for similarities and differences and to inform hypotheses concerning possible formation mechanisms our results show the clastic polygons do not have any morphometric features that indicate they are similar to terrestrial sorted clastic polygons formed by freeze thaw processes they are too large do not show the expected variation in form with slope and have clasts that do not scale in size with polygon diameter however the clastic networks are similar in network morphology to thermal contraction cracks and there is a potential direct martian analogue in a sub type of thermal contraction polygons located in utopia planitia based upon our observations we reject the hypothesis that polygons located around lyot formed as freeze thaw polygons and instead an alternative mechanism is put forward they result from the infilling of earlier thermal contraction cracks by wind blown material which then became compressed and or cemented resulting in a resistant fill erosion then leads to preservation of these polygons in positive relief while later weathering results in the fracturing of the fill material to form angular clasts these results suggest that there was an extensive area of ice rich terrain the extent of which is linked to ejecta from lyot crater

geophysical characteristics of dacite volcanism the 1977 1978 eruption of usu volcano abstract the 1977 1978 eruption of usu volcano is discussed from the geophysical standpoint as a classic example of dacite volcanism the activities of dacitic volcanoes are characterized by persistent earthquake swarms and remarkable crustal deformations due to the high viscosity of the magmas the former include shocks felt near the volcanoes and the latter accompany formation of lava domes or cryptodomes the hypocenters of the earthquakes occurring beneath usu volcano have been located precisely their distribution defines an earthquake free zone which underlies the area of doming within the summit crater this zone is regarded as occupied by viscous magma the domings within the summit crater forming the cryptodomes have amounted to about 160 m in addition to uplift they showed thrusting towards the northeast as a result the northeastern foot of the volcano has contracted by about 150 m the relation between crustal deformation and earthquake occurrence is examined and it is found that the abrupt domings are accompanied by the larger earthquakes m 3 4 3 both the seismic activity and the ground deformation are shown to have a unique and common energy source the energy of activities of usu volcano consists of the explosive type the deformation type and the seismic type the second and the third are in parallel with each other in discharges and both energies are complementary to the explosive energy the explosive energy and the seismic energy have been calculated for an explosion sequence and it is concluded that the deformation energy is about 10 times greater than the seismic energy the discharge rate of the seismic energy and the upheaval rates of the cryptodomes have continued to decrease since the outburst of the eruption except for a small increase at the end of january 1978 eruptions are governed not only by the supply of the energies but also by the depth of the magma which has gradually approached the surface the last eruption occurred in october 1978 however the crustal deformations and the earthquake swarms are still proceeding as of january 1980 albeit at a lower rate of activity

characteristics of micro earthquake swarms preceding eruptions at showa crater of sakurajima volcano japan abstract the showa crater of sakurajima an andesitic volcano in japan resumed eruptive activity in june 2006 for the first time in 58 years explosive eruptions at the showa crater have been active since 2009 micro earthquake swarms have sometimes been observed in the 1 or 2 h preceding these eruptions since 2012 and have frequently occurred during periods of low eruptive activity these precursory micro earthquakes are dominated by high frequency 5 6 hz components and no clear s wave and are thus classified as bh type earthquake swarms the hypocenters of the earthquakes are located in a shallow region depth of approximately 1 km near the showa crater prior to the eruptions the onset of inflation has been observed by extensometers followed by precursory earthquake swarms 30 min to 1 h later in the case of insufficient ground contraction the precursory earthquakes reoccur when the strain reaches the same level it showed just before the eruptions occurred from the occurrence period and pattern of the precursory earthquakes it appears they may be generated within a narrow conduit leading to the showa crater

thermal contraction crack polygons on mars classification distribution and climate implications from hirise observations morphology is shown to be consistent with thermal contraction cracking of an ice rich mantling unit consistent with observations of sediment wedge thermal contraction crack polygons forming in ice cemented sediment at the phoenix landing site polygon groups are distributed symmetrically in both northern and southern hemispheres suggesting strong climate controls on polygon morphology northern hemisphere polygonally patterned surfaces are found to decrease in age from low to high latitude spanning surface ages from 1 to 0 1 ma suggesting more recent deposition of ice rich material at high latitudes than at low latitudes six of the seven classes of polygons are interpreted to be capable of forming because of the combined effects of thermal contraction cracking and differential sublimation suggesting that sublimation and sand wedge polygons dominate martian high latitudes gully polygon systems present at midlatitudes suggest that small amounts of liquid water may have been involved in thermal contraction crack polygon processes producing composite wedge polygons no evidence is found for the presence of pervasive small scale ice wedge polygons

tectonic effects of climate change on venus venusian plains regions are commonly crossed by small strain deformation features such as wrinkle ridges polygonal terrains and gridded terrains of these polygonal terrains are observed to have a relatively uniform spacing and are widely distributed on plains that formed during global resurfacing models of venusian climate that assume resurfacing occurred through massive volcanic events suggest that surface temperatures could have dramatically changed over nearly a billion years propagating thermal stresses into the surface and potentially causing small strain features we investigate this hypothesis by approximating the temperatures predicted by climate models as a step function and employ a fixed plate and strength envelope model to predict the resulting depth of failure and amount of strain our calculations indicate that strains due to temperature changes of 50 100 k which are favored for volcanic resurfacing events of 1 10 km thickness are consistent with the observed spacing of polygonal and gridded terrains as well as some wrinkle ridges the global nature of the climate change event is consistent with the global distribution and uniformity of such features and implies that such terrains may be a global stratigraphic marker

crater floor polygons desiccation patterns of ancient lakes on mars 1 global mapping of intermediate size 100 200 m polygonal troughs occurring mainly in impact crater floors was carried out using high resolution images from spacecraft currently orbiting mars earlier works have classified these polygonal networks as periglacial features on account of their apparent occurrence at higher latitudes and morphological similarities to thermal contraction polygons tcps crater floor polygons cfps have diameters ranging from 15 to 350 m they morphologically resemble terrestrial tcps and desiccation cracks their size distribution however is significantly different from that of tcps that are ubiquitous in the high latitudes an analytical model based on fracture mechanics reveals that under current climatic conditions the maximum fracture spacing attainable by thermal stresses alone is 75 m at the most more reasonable values fall within 18 and 22 m which is the range for tcps on mars as a result we propose desiccation to be a dominant mechanism for the formation of cfps without ruling out thermal contraction as a possible contributor in some cases this implies that lakes or water rich sediments occupied the craters in the past many such aqueous environments have no apparent external source of water and thus hydrothermal processes occurring shortly after the impact event may be viable explanations for the observed evidence the association of features which correspond to terrestrial lakes such as sedimentary deposits mounds and shorelines corroborates lake formation and their eventual desiccation to form cfps the variation of cfp sizes with location can be indicative of different hydrologic environments

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

precursory changes in seismic velocity for the spectrum of earthquake failure modes temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviors including slow earthquakes tremor and low frequency earthquakes1 laboratory and theoretical studies predict changes in seismic velocity prior to earthquake failure2 however tectonic faults fail in a spectrum of modes and little is known about precursors for those modes3 here we show that precursory changes of wave speed occur in laboratory faults for the complete spectrum of failure modes observed for tectonic faults we systematically altered the stiffness of the loading system to reproduce the transition from slow to fast stick slip and monitored ultrasonic wave speed during frictional sliding we find systematic variations of elastic properties during the seismic cycle for both slow and fast earthquakes indicating similar physical mechanisms during rupture nucleation our data show that accelerated fault creep causes reduction of seismic velocity and elastic moduli during the preparatory phase preceding failure which suggests that real time monitoring of active faults may be a means to detect earthquake precursors

seismic stereometry reveals preparatory behavior and source kinematics of intermediate size earthquakes although moderate size earthquakes are poorly studied by lack of near fault observations they can provide key information about larger damaging earthquakes here we propose a new approach inspired by double difference relocation that uses high coherency waveforms recorded at neighboring sensors to study the preparation phase and dynamics of moderate size earthquakes we validate this technique by analyzing the 2016 m w 5 2 borrego springs earthquake in southern california and find consistent rupture velocities of 2 km s highlighting two main rupture asperities the analysis of the 2019 ml5 2 le teil earthquake in france reveals slow nucleation at depth that migrates to the surface and propagates northward with a velocity of 2 8 km s highlighting two main rupture events also imaged by insar by providing unprecedented resolution in our observation of the rupture dynamics this approach will be useful in better understanding the preparation phase and rupture of both tectonic and induced earthquakes plain language summary small and moderate size earthquakes are much more numerous yet studied in much less detail than large and damaging earthquakes this is because to study small earthquakes precisely one needs seismometers very close to the rupture which is rarely the case it is still unclear if small and large earthquakes start the same way thus studying more systematically small earthquakes could help to answer this question here we show that we can use two close by seismometers as we would do with 3 d glasses to observe with a stereoscopic effect the evolution of intermediate size earthquakes when they rupture along a fault we can retrieve the direction of rupture the speed at which the fault breaks and the length of the rupture important parameters that help to characterize the earthquakes using this new method we can sometimes also observe the behavior of the fault before the main rupture which will be useful to better understand how earthquakes start

the periglacial landscape at the phoenix landing site 1 the mars scout mission phoenix landed in the northern high latitudes of mars in an area thought to be dominated by subsurface ground ice and has provided a unique detailed examination of periglacial morphology and topography that is not visible from orbit the landing site and surrounding terrain is dominated by polygonal patterned ground typical of the martian northern plains the polygons exhibit a gentle u shaped trough and rounded mound topography with an average trough depth of 17 cm and an average surface slopes of only 6 7 polygons an average 4 3 m across form a pattern superimposed on all other geologic landforms including larger 20 25 m polygons and kilometer long linear ridges the polygon morphology and the predominance of subsurface ice cemented soil are consistent with the formation of subsurface sand wedges in a permanently frozen arid climate small scale soil furrows and cracks into the ice cemented soil indicate that the thermal contraction process responsible for the formation of the polygons is active today rocks appear to be sorted within the polygon troughs indicating a process of cryoturbation within the permanently frozen polygons the complexity of the patterns crosscutting relations and rock distributions indicate advanced maturity of the polygon networks and shifting crack patterns possibly facilitated by crack and wedge annealing during times of low obliquity

controls of conduit geometry and wallrock elasticity on lava dome eruptions abstract many lava dome building eruptions show periodic to complex non periodic pulsatory activity typical time scales associated with this activity range from hours to decades previous studies modelled the ascent of magma using a set of transient 1 d transport equations accounting for degassing induced crystallization kinetics gas exsolution and viscosity increase due to crystal growth these models assumed flow in a cylindrical conduit with a fixed cross section area since several observations suggest that extrusions are mainly fed by dykes with cylindrical geometries developing only at shallow levels here we generalised the model to the flow geometry represented by an elliptical dyke with major and minor semi axes changing with depth quasi static elastic deformation of the dyke is accounted by an analytical solution that couples cross section area with the magmatic overpressure the effects of the main dyke geometrical parameters and boundary conditions on the eruption dynamics were investigated the presence of a deformable dyke can lead to a more complex periodic behaviour with a wider range of time scales and cyclicity patterns with respect to a uniform cylindrical conduit there is a regime where the period of pulsations is controlled by the elasticity of the dyke and a regime where the period is controlled by the volume of the magma chamber intermediate regimes are possible periodic variations in discharge rate are also possible for both fixed pressure in dyke source region and fixed influx rate into the dyke our study emphasizes the strong non linearities and complex behaviours of lava dome eruptions from a forecasting and hazard perspective intrinsic uncertainties in governing parameters may make volcanic systems in some circumstances unpredictable on the other hand lava dome systems may also develop episodic and systematic behaviours so that behaviour becomes predictable for a while

global distribution of neutrons from mars results from mars odyssey global distributions of thermal epithermal and fast neutron fluxes have been mapped during late southern summer northern winter using the mars odyssey neutron spectrometer these fluxes are selectively sensitive to the vertical and lateral spatial distributions of h and co 2 in the uppermost meter of the martian surface poleward of 60 latitude is terrain rich in hydrogen probably h 2 o ice buried beneath tens of centimeter thick hydrogen poor soil the central portion of the north polar cap is covered by a thick co 2 layer as is the residual south polar cap portions of the low to middle latitudes indicate subsurface deposits of chemically and or physically bound h 2 o and or oh