mineralogy and fluid inclusion investigations in the reagan porphyry system iran the path to an uneconomic porphyry copper deposit abstract the reagan porphyry system in southeastern iran kerman province is associated with diorite granodiorite to quartz monzonitic rocks of miocene age three stages of hydrothermal alteration and associated mineralization have produced new minerals created new textural relationships and in many cases obliterated the primary character of the rocks potassic phyllic and propylitic are the main hydrothermal alteration types within the intrusive stock the early hydrothermal alteration produced a potassic assemblage in the central part of the stock propylitic alteration occurred contemporaneously with potassic alteration but in the peripheral parts phyllic alteration which contains the main copper mineralization occurred later overprinting the earlier alteration phyllic is also the major alteration in the reagan system the early hydrothermal fluids are represented by high temperature 487 598 c high salinity up to 61 1 wt nacl equiv liquid rich fluid inclusions and high temperature 397 401 c low salinity vapor rich inclusions which are interpreted to originate from very hot orthomagmatic fluids the brines are interpreted to have caused potassic alteration producing first generation chalcopyrite propylitic alteration is attributed to a lower temperature liquid and ca rich evolved meteoric fluid influx of meteoric water into the system and mixing with magmatic fluid produced deep albitization and shallow phyllic alteration this influx also caused dissolution of early formed copper sulfides and remobilization of cu into the phyllic zone the following data indicate that the mineralizing fluid temperature was too high to produce an economic porphyry copper deposit at the studied area supergene alteration was restricted to a very thin blanket with uneconomic levels of cu in the form of cu sulfides and oxides

rare earth element signatures of economic and sub economic porphyry copper systems in urumieh dokhtar magmatic arc udma iran abstract a wide variety of porphyry copper deposits have been reported along the cenozoic urumieh dokhtar magmatic arc in iran the formation of these deposits is attributed to closure of neo tethys and the subsequent collisional tectonic regime during the tertiary this study presents whole rock rare earth element ree data for the giant to small sarcheshmeh meiduk sungun darreh zerreshk dalli iju parkam and ali abad with sub economic daraloo and reagan porphyry copper systems the data indicate a temporal and geochemical evolution from sub economic porphyry systems to economic deposits all the economic and sub economic porphyry copper systems exhibit lree enrichment relative to hree whereas the economic deposits exhibit a relatively steep downward lree to hree profile reflecting higher lree abundance the eu anomalies vary from distinct negative in sub economic deposits eu eu 0 28 0 70 to either markedly less negative or positive anomalies eu eu 0 45 1 67 in economic deposit the economic porphyry deposits are characterized by relatively high la sm and sm yb values representing high crustal assimilation in a relatively thickened crust and provide insight into fractionation of hornblende with minor garnet in deep crustal parts mash zone compared with sub economic deposits the steep downward lree to mree and flatter to slightly upward mree to hree in economic deposits indicate hornblende involvement magma evolution toward more volatile content it seems that in an ongoing process of closure of neo tethys during compression and crustal shortening the early eocene oligocene sub economic intrusions are followed by adakite like hydrous miocene and younger economic cu bearing intrusions

geochemistry and fluid characteristics of the dalli porphyry cu au deposit central iran abstract the miocene dalli porphyry cu au deposit in the central part of urumieh dokhtar magmatic arc is the first reported au rich porphyry cu deposit in the zagros orogenic belt the cu au mineralization is mainly hosted in diorite and quartz diorite intrusions presenting as numerous veinlets in the altered wall rocks with potassic phyllic and propylitic alteration developed based on the mineral assemblages and crosscutting relations of veinlets hydrothermal mineralization alteration occurred in at least three stages characterized by veinlets of 1 qtz kfs mag ccp 2 qtz py ccp bn cv cc and 3 qtz chl bt the ore bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas including lree fractionated pattern strong enrichment in lile cs rb ba pb and u and depletion of hfse with marked negative ti and nb anomalies the adakite like ore hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of y and eu eu with increasing sio2 content respectively moreover they exhibit a significant increasing trend of sr y with decreasing of y which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma a relatively flat hree pattern with low dyn ybn and nb ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust based on the phase assemblages confirmed by detailed laser raman spectroscopy analyses and proportion of solid liquid and gaseous components five types of fluid inclusions were recognized which are categorized as 1 liquid rich two phase liquidh2o vaporh2o iia 2 vapor rich two phase vaporh2o co2 liquidh2o iib 3 high saline simple fluids iiia liquidh2o vaporh2o hl 4 high saline opaque mineral bearing fluids iiib liquidh2o vaporh2o hl hem ccp py and 5 multi phase type iiiab liquidh2o vaporh2o hl anh hem mag ccp in early stage veins the homogenization temperature of multiphase inclusions as high as 620 c with corresponding salinities of up to 75 wt nacl equivalent represent the initial ore forming fluids from early to late stage veins the gradual decrease of homogenization temperature of saline inclusions iiiab iiia and iiib from 620 to 340 c corresponding salinities of 75 35 wt nacl equivalent may reflect fluid boiling and mixing of the early magmatic fluids with circulating groundwater the common association of hematite and anhydrite daughter phases with the most primitive inclusions iiiab in early stage veins and the lack of co2 bearing inclusions in the middle to late stage veins reveal co2 content and oxygen fugacity of the fluids was significantly decreased from early to main stage of sulfide mineralization second generation of veins it seems that magnetite crystallization and co2 escape have a decisive role in oversaturation of s2 and subsequent rapid and large scale precipitation of sulfides in second generation of veins at the dalli deposit

factors controlling copper solubility and chalcopyrite deposition in the sungun porphyry copper deposit iran the sungun porphyry copper deposit is hosted in a diorite granodioritic to quartz monzonitic stock that intruded eocene volcanosedimentary and cretaceous carbonate rocks copper mineralization is associated mainly with potassic alteration and to a lesser extent with sericitic alteration based on previously published fluid inclusion and isotopic data by hezarkhani and williams jones most of the copper is interpreted to have deposited during the waning stages of orthomagmatic hydrothermal activity at temperatures of 400 to 300 c these data also indicate that the hydrothermal system involved meteoric waters and boiled extensively in this work thermodynamic data are used to delineate the stability fields of alteration and ore assemblages as a function of fs2 fo2 and ph the solubility of chalcopyrite was evaluated in this range of conditions using recently published experimental data during early potassic alteration 450 c copper solubility is calculated to have been 50 000 ppm whereas the copper content of the initial fluid responsible for ore deposition is estimated from fluid inclusion data to have been 1200 3800 ppm this indicates that initially the fluid was highly undersaturated with respect to chalcopyrite which agrees with the observation that veins formed at t 400 c contain molybdenite but rarely chalcopyrite copper solubility drops rapidly with decreasing temperature and at 400 c is approximately 1000 ppm within the range estimated from fluid inclusion data whereas at 350 c it is only 25 ppm these calculations are consistent with observations that the bulk of the chalcopyrite deposited at sungun is hosted by veins formed at temperatures of 360 60 c other factors that in principle may reduce chalcopyrite solubility are increases in ph and decreases in fo2 and acl our analysis shows however that most of the change in ph occurred at high temperature when chalcopyrite was grossly undersaturated in the fluid and that the direction of change in fo2 increased chalcopyrite solubility we propose that the sungun deposit formed mainly in response to the sharp temperature decrease that accompanied boiling and partly as a result of the additional heat loss and decrease in acl which occurred as a result of mixing of acidic cu bearing magmatic waters with cooler meteoric waters of lower salinity

chemical analyses of halite trend inclusions from the granisle porphyry copper deposit british columbia high salinity fluid inclusions from many porphyry copper and skarn deposits fall on linear trends in the h 2 o nacl kcl system called the halite trend and they have been interpreted to result from separation of kcl bearing halite before entrapment of the fluid in the inclusion in addition to na k and cl halite trend inclusions can also contain abundant fe ca and s all of which could have an effect on the orientation of the trend in the h 2 o nacl kcl system making halite subtraction a less likely explanation for the observed compositional trend we have attempted to evaluate this possibility by analysis of inclusion daughter minerals decrepitates and leachates as well as phase volume measurements for daughter minerals in fluid inclusions from the granisle porphyry copper deposit these observations show that fecl 2 composes 31 to 45 wt percent of the inclusion and that the resulting halite trend inclusion salinities range from 70 to 84 wt percent of nacl kcl fecl 2 cacl 2 and mncl 2 are minor components the liquid contains smaller but significant amounts of sulfur probably as hso super 4 and its complexes as well as co 2 co and ch 4 in minor amouns trends established by these data point toward nacl in multicomponent space thus supporting halite or halite solid solution subtraction over the alternative mechanisms proposed to explain the halite trend

sources of tsunami and tsunamigenic earthquakes in subduction zones we classified tsunamigenic earthquakes in subduction zones into three types earth quakes at the plate interface typical interplate events earthquakes at the outer rise within the subducting slab or overlying crust intraplate events and tsunami earthquakes that generate considerably larger tsunamis than expected from seismic waves the depth range of a typical interplate earthquake source is 10 40km controlled by temperature and other geological parameters the slip distribution varies both with depth and along strike recent examples show very different temporal change of slip distribution in the aleutians and the japan trench the tsunamigenic coseismic slip of the 1957 aleutian earthquake was concentrated on an asperity located in the western half of an aftershock zone 1200km long this asperity ruptured again in the 1986 andreanof islands and 1996 delarof islands earthquakes by contrast the source of the 1994 sanriku oki earthquake corresponds to the low slip region of the previous interplate event the 1968 tokachi oki earthquake tsunamis from intraplate earthquakes within the subducting slab can be at least as large as those from interplate earthquakes tsunami hazard assessments must include such events similarity in macroseismic data from two southern kuril earthquakes illustrates difficulty in distinguishing interplate and slab events on the basis of historical data such as felt reports and tsunami heights most moment release of tsunami earthquakes occurs in a narrow region near the trench and the concentrated slip is responsible for the large tsunami numerical modeling of the 1996 peru earthquake confirms this model which has been proposed for other tsunami earthquakes including 1896 sanriku 1946 aleutian and 1992 nicaragua

low frequency source characteristics of the great 1960 chilean earthquake the low frequency nature of the great 1960 chilean earthquake the earth s largest recorded event is characterized and a source model composed of three events with a combined seismic moment of 5 5 1023 n m and a duration of 1500 s is presented the results show conclusively that large scale slip which is only observed at low frequencies preceded the main shock complex amplitude measurements of normal mode data in the band 1 0 5 0 mhz recorded at eight vertical component stations comprise the data set in this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity the data set is the basis for a sequence of least squares inversions to determine the seismic moment rupture velocity spatial slip distribution and the temporal slip function the data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1 9 1023 n m and rise time of 300 s a main shock with moment of 3 2 1023 n m and for which most of the low frequency energy was released beginning about 50 s after the short period origin time and an event 350 s later with moment of 0 4 1023 n m the uncertainty in the moment estimate of the great 1960 chilean earthquake is about 50 and is due primarily to the probable range of fault plane dip which is not well constrained at this time

the origin of granite the role and source of water in the evolution of granitic magmas temperature and water content are the two most important parameters in the formation of granitic magmas evidence from volcanic and plutonic lithologies suggests that water contents of 2 to 4 wt are present in most silicic magmas calculations based on the stability of biotite yield water fugacities within the melt phase from about 500 to 2 000 bars although these calculations determine the log f h 2 o and the effective uncertainty of 0 5 log units yields a large absolute uncertainty comparison with crystallization experiments demonstrates that less than 2 water would require significant percentages of crystallization at temperatures above 900 c with liquidus temperatures about 1000 c water contents greatly in excess of 4 wt would mean that the magma would become vapor saturated at high pressures and would tend to crystallize during ascent to a fine grained granite before reaching shallow depths the main sources of water for magma generation are the dehydration of hydrous silicates within the crust and volatiles transported into the crust from subducted oceanic crust and upper mantle in the form of hydrous basalts and andesites dehydration reactions of muscovite biotite and horn blende are of particular significance anatectic granites may be partially classified in terms of the probable dehydration reaction responsible for their generation melts generated from muscovite dehydration are relatively cool peraluminous in composition high in k na ratio and generally high in initial 87 sr 86 sr and delta 18 o biotite generated melts tend to be higher in temperatures peraluminous to meta aluminous in composition moderately high in k na ratio and relatively high in strontium and oxygen ratios both types may contain metasedimentary enclaves granitoids generated by hornblende dehydration would be much higher in initial temperature peralka line to meta aluminous in composition and lower in k na ratio and in general would have lower strontium and oxygen ratios volatiles deposited in hydrothermally altered oceanic crust and upper mantle will be released during subduction in the form of hydrous basalts and andesites these melts are important energy transfer mechanisms to drive anatexis within the crust if these melts encounter a silicic magma chamber when intruding the crust they will be trapped below the lower density granitic melt while partially quenching against the cooler melt they may release volatiles and heat which will aid in the melting process granites generated in this way will vary in their geochemical properties depending on the relative importance of crustal versus mantle magma systems in general they will have moderate to high initial temperatures be meta aluminous in composition be variable but somewhat low in k na ratio and have lower initial strontium and delta 18 o ratios than will melts derived completely from the crust the fact that most terrestrial spreading centers are subaqueous thus may aid in the formation of a thick granitic continental crust

the 1996 peru tsunamigenic earthquake broadband source process we investigate the spatio temporal complexity of moment release of the february 21 1996 peru earthquake mw 7 5 we use a non linear source tomographic technique based on simulated annealing to invert surface wave source spectra for the slip distribution on a gently dipping fault plane the spectra 5 65 mhz are obtained using an empirical green s function egf method applied to first and second orbit fundamental mode rayleigh waves spectra are well fit by a 110 km bilateral rupture subparallel to the trench updip of the hypocenter with a total moment of 2 0 1020 nm the non linear inversion reveals a 30 30 km major slip patch south the onset where rupture velocities attain 1 5 2 0 km s inversions of teleseismic broadband p and sh waves 10 500 mhz indicate little or no directivity consistent with the surface wave data the average source time functions for both the surface and body wave data are similar in shape and in duration 50 s part of the slip during the 1996 peru event occurred in a region of reduced background seismicity as was the case for the 1992 nicaragua slow event suggesting that the seismogenic potential of low seismicity regions near the trench should be globally reassessed

geochemical characteristics of collisional and pre collisional porphyry copper systems in kerman cenozoic magmatic arc iran using plagioclase biotite and amphibole chemistry abstract kerman cenozoic magmatic arc kcma located in the southeastern part of urumieh dokhtar magmatic bet udmb hosts a number of world class and moderate to small porphyry copper deposits the present work compares the silicate chemistry plagioclase biotite and amphibole of miocene collisional porphyries e g chahfiruzeh and keder with eocene oligocene pre collisional porphyry systems e g reagan and daralou in the kcma p 1 imply water rich nature of studied porphyry systems the relative enrichment f in the collisional porphyry deposits e g keder could be linked with enrichment of mg in these systems

extreme runup from the 17 july 2006 java tsunami 1 the 17 july 2006 magnitude mw 7 8 earthquake off the south coast of western java indonesia generated a tsunami that effected over 300 km of coastline and killed more than 600 people with locally focused runup heights exceeding 20 m this slow earthquake was hardly felt on java and wind waves breaking masked any preceding withdrawal of the water from the shoreline making this tsunami difficult to detect before impact an international tsunami survey team was deployed within one week and the investigation covered more than 600 km of coastline measured tsunami heights and run up distributions were uniform at 5 to 7 m along 200 km of coast however there was a pronounced peak on the south coast of nusa kambangan where the tsunami impact carved a sharp trimline in a forest at elevations up to 21 m and 1 km inland local flow depth exceeded 8 m along the elevated coastal plain between the beach and the hill slope we infer that the focused tsunami and runup heights on the island suggest a possible local submarine slump or mass movement

slow earthquakes and great earthquakes along the nankai trough abstract we have reexamined reports indicating that slow deformation occurred before the great japan earthquakes of 1944 tonankai and 1946 nankaido and find that the observations are well founded although no quantitative models have previously been proposed to explain all of the relevant data we show that they are satisfied by a simple model for both earthquakes the model based on known properties of subduction zones has slow slip on the subduction interface in an area deeper than the seismic rupture if this model is correct and a similar physical situation holds for an anticipated tokai earthquake existing instruments will be able to reveal the pre slip in real time while differences among the deformation time series at different sites will provide strong constraints on the slow rupture propagation these differences could result in delaying the recognition of a coherent event

the 25 october 2010 mentawai tsunami earthquake mw 7 8 and the tsunami hazard presented by shallow megathrust ruptures the 25 october 2010 mentawai indonesia earthquake m w 7 8 ruptured the shallow portion of the subduction zone seaward of the mentawai islands off shore of sumatra generating 3 to 9 m tsunami run up along southwestern coasts of the pagai islands that took at least 431 lives analyses of teleseismic p sh and rayleigh waves for finite fault source rupture characteristics indicate 90 s rupture duration with a low rupture velocity of 1 5 km s on the 10 dipping megathrust with total slip of 2 4 m over an 100 km long source region the seismic moment scaled energy release is 1 4 10 6 lower than 2 4 10 6 found for the 17 july 2006 java tsunami earthquake m w 7 8 the mentawai event ruptured up dip of the slip region of the 12 september 2007 kepulauan earthquake m w 7 9 and together with the 4 january 1907 m 7 6 tsunami earthquake located seaward of simeulue island to the northwest along the arc demonstrates the significant tsunami generation potential for shallow megathrust ruptures in regions up dip of great underthrusting events in indonesia and elsewhere

a unified source model for the 2011 tohoku earthquake abstract the devastating 2011 tohoku earthquake was observed by dense networks of geophysical instruments a unified source model was constructed through joint inversion of teleseismic strong motion and geodetic datasets the result indicates that the earthquake consists of three main ruptures after small rupture in the initial 50 s the first rupture expanded at a slow speed of 1 8 km s to the northeast and east the second rupture began 20 s later at the slowest speed of 1 5 km s and became dominant with the largest slip of 36 m the third rupture then played the leading role propagating southward at a speed of 2 5 km s only the tsunami inversion requires an extension of the source fault to a shallow part between the first rupture area and the japan trench recovering tsunamigenic slips larger than 40 m the slow rupture speed and tsunamigenic slips can explain the features of the disaster by the earthquake

overview of holocene tsunami deposits along the nankai suruga and sagami troughs southwest japan tsunami deposits provide a basis for reconstructing holocene histories of great earthquakes and tsunamis on the pacific coast of southwest japan the deposits have been found in the past 15 years at lakes lagoons outcrops and archaeological excavations the inferred tsunami histories span 3000 years for the nankai and suruga troughs and nearly 10 000 years for the sagami trough the inferred histories contain recurrence intervals of variable length the shortest of these 100 200 years for the nankai trough 150 300 years for the sagami trough resemble those known from written history of the past 1000 1500 years longer intervals inferred from the tsunami deposits probably reflect variability in rupture mode incompleteness of geologic records and insufficient research the region s tsunami history could be clarified by improving the geologic distinction between tsunami and storm dating the inferred tsunamis more accurately and precisely and using the deposits to help quantify the source areas and sizes of the parent earthquakes

partial rupture of a locked patch of the sumatra megathrust during the 2007 earthquake sequence the great sumatra andaman earthquake and tsunami of 2004 was a dramatic reminder of the importance of understanding the seismic and tsunami hazards of subduction zones 1 2 3 4 in march 2005 the sunda megathrust ruptured again producing an event 5 of moment magnitude mw 8 6 south of the 2004 rupture area which was the site of a similar event in 1861 ref 6 concern was then focused on the mentawai area where large earthquakes had occurred in 1797 mw 8 8 and 1833 mw 9 0 6 7 two earthquakes one of mw 8 4 and twelve hours later one of mw 7 9 indeed occurred there on 12 september 2007 here we show that these earthquakes ruptured only a fraction of the area ruptured in 1833 and consist of distinct asperities within a patch of the megathrust that had remained locked in the interseismic period this indicates that the same portion of a megathrust can rupture in different patterns depending on whether asperities break as isolated seismic events or cooperate to produce a larger rupture this variability probably arises from the influence of non permanent barriers zones with locally lower pre stress due to the past earthquakes the stress state of the portion of the sunda megathrust that had ruptured in 1833 and 1797 was probably not adequate for the development of a single large rupture in 2007 the moment released in 2007 amounts to only a fraction both of that released in 1833 and of the deficit of moment that had accumulated as a result of interseismic strain since 1833 the potential for a large megathrust event in the mentawai area thus remains large

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

coseismic slip resolution along a plate boundary megathrust the nankai trough southwest japan geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 tonankai mw 8 1 and 1946 nankaido mw 8 3 earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust data used include 798 angle changes from triangulation surveys 328 leveling section differences and 5 coseismic tidal gage offsets many of the nominally coseismic triangulation data span 50 years nearly half the earthquake cycle and correction for interseismic deformation using post 1950 observations is applied microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous multisegment fault model because the onshore geodetic data have very limited resolving power for offshore fault segments offshore coseismic slip was constrained by satake s 1993 estimation based on tsunami data the majority of the coseismic slip occurs between 15 and 25 km depth although resolution declines toward the trench axis it is sufficiently good to define two distinct high slip regions one off southeastern shikoku island 11 m maximum and the other offshore of kii peninsula 3 m maximum the slip magnitude off southeastern shikoku coupled with the plate convergence rate would imply an recurrence interval of about 270 years much longer than the average repeat time of 120 years for historical great earthquakes on the nankai trough however the maximum coseismic slip is sensitive to the assumed fault geometry and slippage on trough parallel splay faults could significantly decrease the maximum slip to about 6 m

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

the tsunami earthquake of 1932 june 22 in manzanillo mexico seismological study and tsunami simulations summary we conduct a detailed seismological study of the large colima mexico earthquake of 1932 june 3 and of its aftershocks of june 18 and 22 the latter event iii generated a tsunami more devastating than that of the main shock despite much smaller seismic magnitudes thus qualifying as a so called tsunami earthquake relocation based on published arrival times shows that event iii took place up dip of the main shock the analysis of the spectral amplitude of mantle surface waves yields low frequency moments of 24 5 2 and 4 times 1027 dyn cm respectively with event iii featuring a moment growing with period which expresses the source slowness characteristic of tsunami earthquakes this is confirmed by a deficient energy to moment ratio as derived from high frequency p waves recorded at pasadena near field hydrodynamic simulations show that the effects of the main shock s tsunami are well modelled by a standard seismic source whereas the stronger tsunami from event iii can be modelled by rupture along a splay fault in a mechanically deficient material all our results then fit the model for tsunami earthquake aftershocks proposed for the kuril islands by fukao in 1979

the 17 july 2006 java tsunami earthquake the 17 july 2006 java earthquake involved thrust faulting in the java trench and excited a deadly tsunami 5 8 m that inundated the southern coast of java the earthquake s size estimates vary significantly with seismic wave period very long period signals 300 500 s indicate a seismic moment of 6 7 10 20 nm m w 7 8 m s 20 s 7 2 m b 1 s 6 2 while shaking intensities 3 10 hz were mmiv the large tsunami relative to ms characterizes this event as a tsunami earthquake like previous tsunami earthquakes the java event had an unusually low rupture speed of 1 0 1 5 km s and occurred near the up dip edge of the subduction zone thrust fault most large aftershocks involved normal faulting the rupture propagated 200 km along the trench with several pulses of shorter period seismic radiation superimposed on a smooth background rupture with an overall duration of 185 s

state of stress in the northern gulf coast conspicuous structural features of the northern gulf coast are regional systems of listric normal faults formed contemporaneously with deposition periods of main fault movement range from eocene to miocene initial development of these contemporaneous fault systems is usually attributed to differential compaction and or gravity sliding within the sedimentary section during clastic sedimentation on a stable shelf evidence of recent reactivation of some fault systems indicates that sediments in the region are currently in a tensional state of stress infrequent low to moderate intensity earthquakes also are associated with the faulted region lithospheric flexure due to sediment loading has been suggested as a possible cause of this extensional regime for most passive continental margins sedimentation alone is not sufficient to cause flexurally induced faulting and earthquakes because the sediment load accumulates slowly enough for the stresses to relax however sedimentation rates in the northern gulf coast have been extremely high since the pleistocene 12 18 cm 100 yr a simple flexural calculation yields horizontal extension normal faulting in the lower gulf coast caused by the weight of pleistocene sediments although the relationship between basement upwarp and surface uplift may be complicated by subsidence due to compaction of sediment the location of the flexural bulge due to loading by pleistocene and younger sediments is generally consistent with areas of recent uplift determined from releveling data bending stresses caused by the total weight of mesozoic and cenozoic sediments predict horizontal compression for this region indicating that most of these stresses must have relaxed relaxation of stresses over time may also explain the absence of large earthquakes

tsunami earthquakes as transient phenomena 1 recent modeling of tsunami waveforms caused by tsunami earthquakes indicates that fault slip occurred along the subduction boundary close to the trench axis on the other hand it is well known that seismicity is generally very low within ca 50 km from the trench axis and this has been attributed to the stable frictional sliding properties of the subducted unconsolidated sediments this makes tsunamigenic slip near the trench difficult to explain in order to solve this dilemma i propose that transition from stable sliding to nearly zero friction with a velocity weakening property occurs as a result of areal increase of zones of elevated fluid pressure which may make fairly rapid seismic slip possible following the breakage of asperities at normal seismogenic depths this transition can be identified as seismic reflections with negative polarities which may help to rate hazards for a coming large tsunami earthquake