periodic variation of stress field in the koyna warna reservoir triggered seismic zone inferred from focal mechanism studies abstract the koyna warna region in western india is globally recognized as the premier site of reservoir triggered seismicity rts associated with the koyna and warna reservoirs the region is characterized by continuous seismic activity observed since several decades including the world s largest triggered earthquake of m6 3 which occurred in koyna in 1967 while the role of reservoirs in triggering earthquakes has been widely discussed the actual tectonic mechanism controlling earthquake genesis in this region is hardly understood the koyna warna region is exclusively governed by earthquakes of strike slip and normal fault mechanism distinct from the thrust faulting seen in other active zones in the indian region in the present study a comprehensive catalog of 50 focal mechanism solutions of earthquakes that occurred during the last 45 years in the koyna warna region is developed both from previous literature and from moment tensor inversion studies by the authors using broadband data from a local seismic network operating since 2005 the seismicity and fault plane data have enabled precise delineation of trends of the major causative faults which are further accentuated using the double difference technique stress inversion of the focal mechanism data has provided the best fitting principal compressive and tensile stress field of the region which in conjunction with the deciphered fault zones provides a feasible model of seismogenesis in this region based on the observed temporal variation of faulting mechanism a model of alternating cycles of predominantly strike slip and normal faulting is proposed which is attributed to a periodic peaking and relaxation respectively of the horizontal compressive stress field in this region due to the indian plate collision with eurasia

a magnetotelluric mt study across the koyna seismic zone western india evidence for block structure abstract wide band magnetotelluric measurements were carried out at 16 sites along guhaghar sangole traverse across the koyna seismicity zone the results of the study besides providing details of deccan trap thickness variation along the traverse brought out several structural characteristics of the subsurface extending to deep crustal levels the koyna fault zone is characterized by a weak expression of a moderately conductive feature extending only up to a depth of 4 5 km two dimensional modeling results bring out distinct block structure in the koyna region and are compared with velocity and density structure of the region the deep electrical structure is interpreted in terms of lateral lithological heterogeneities

the geodynamic evolution of the internal zone of the betic cordilleras south east spain a model based on structural analysis and geothermobarometry the internal zone of the betic cordilleras consists of several superimposed major thrust sheets with different p t t evolutions on the basis of an integrated field microscopic and laboratory study the tectono metamorphic history of the mulhacen complex and almanzora unit has been reconstructed in detail the mulhacen complex has been af ected by at least five phases of penetrative deformation which have been labelled dx d dx d and dx d and d are related to continent continent collision which is indicated by high pressure low temperature wilt and subsequent intermediate pit metamorphic conditions d is related to crustal thinning and heterogeneous extension during this event the almanzora unit was juxtaposed against the mulhacen complex this phase was succeeded by the establishment of low pressure high temperature lpiht conditions and at least two phases of folding and overthrusting the almanzora unit shows a comparable tectono metamorphic evolution pt d however the pit conditions prior to d indicate a higher crustal position with respect to the mulhacen complex during the collisional event key w alpine orogeny betic cordilleras spain continent continent collision crustal thickening crustal thinning deformation structures geothermobarometry p t t path

new palaeomagnetic data from the mahabaleshwar plateau deccan flood basalt province india implications for the volcanostratigraphic architecture of continental flood basalt provinces abstract new magnetostratigraphic data from seven western ghats sections in the deccan volcanic province are presented these are combined with an established geochemically defined stratigraphy and volcanological logs to provide a correlated chronological eruptive framework we identify two magnetic polarities in five of the sections and these are assigned to chrons 29r and 29n importantly the reversal boundary represents an identifiable isochronous surface within the volcanic pile this surface occurs at different elevations as does the altitude of the geochemically defined formation boundary i e ambenali mahabaleshwar fms which defines a second isochronous surface inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces this indicates that there was significant local topography c 80 m across deccan volcanic province lava fields during their development an interpretation consistent with topographies observed across modern and historical examples e g hawaii iceland these data also indicate that the geochemical stratigraphies of continental flood basalt provinces can mask local and sub regional detail in lava stacking patterns when applied at smaller spatial scales 2 10 4 m finally transitional r n directions preserved in some eruptive units place constraints upon the rates of eruption and indicate c 2 ka periods of volcanic repose

lidar assisted identification of an active fault near truckee california abstract we use high resolution 1 5 2 4 points m 2 bare earth airborne light detection and ranging lidar imagery to identify map constrain and visualize fault related geomorphology in densely vegetated terrain surrounding martis creek dam near truckee california bare earth lidar imagery reveals a previously unrecognized and apparently youthful right lateral strike slip fault that exhibits laterally continuous tectonic geomorphic features over a 35 km long zone if these interpretations are correct the fault herein named the polaris fault may represent a significant seismic hazard to the greater truckee lake tahoe and reno carson city regions three dimensional modeling of an offset late quaternary terrace riser indicates a minimum tectonic slip rate of 0 4 0 1 mm yr mapped fault patterns are fairly typical of regional patterns elsewhere in the northern walker lane and are in strong coherence with moderate magnitude historical seismicity of the immediate area as well as the current regional stress regime based on a range of surface rupture lengths and depths to the base of the seismogenic zone we estimate a maximum earthquake magnitude m for the polaris fault to be between 6 4 and 6 9

analysis of the return period and correlation between the reservoir induced seismic frequency and the water level based on a copula a case study of the three gorges reservoir in china abstract studies have considered the many factors involved in the mechanism of reservoir seismicity focusing on the correlation between reservoir induced seismicity and the water level this study proposes to utilize copula theory to build a correlation model to analyze their relationships and perform the risk analysis the sequences of reservoir induced seismicity events from 2003 to 2011 in the three gorges reservoir in china are used as a case study to test this new methodology next we construct four correlation models based on the gumbel clayton frank copula and m copula functions and employ four methods to test the goodness of fit q q plots the kolmogorov smirnov k s test the minimum distance md test and the akaike information criterion aic test through a comparison of the four models the m copula model fits the sample better than the other three models based on the m copula model we find that for the case of a sudden drawdown of the water level the possibility of seismic frequency decreasing obviously increases whereas for the case of a sudden rising of the water level the possibility of seismic frequency increasing obviously increases with the former being greater than the latter the seismic frequency is mainly distributed in the low frequency region y 20 for the low water level and in the middle frequency region 20 y 80 for both the medium and high water levels the seismic frequency in the high frequency region y 80 is the least likely for the conditional return period it can be seen that the period of the high frequency seismicity is much longer than those of the normal and medium frequency seismicity and the high water level shortens the periods

gps measurements of deformation caused by seasonal filling and emptying cycles of four hydroelectric reservoirs in indiagps measurements of deformation caused by seasonal filling and emptying cycles

five decades of triggered earthquakes in koyna warna region western india a review abstract we review reservoir triggered seismicity rts in the koyna warna region of india since the impoundment of the koyna reservoir in 1962 until the year 2015 we include seismicity that occurred farther south in response to the impoundment of warna reservoir in 1993 about 35 km to the south of koyna reservoir the on going earthquake activity for more than five decades in a small seismic volume of about 30 20 10 km3 has characterized the koyna warna region as globally unique and significant to date 22 earthquakes of m 5 about 200 earthquakes of m 4 and several thousand smaller earthquakes have been recorded by a dense network of stations in the region various seismological geophysical and hydrological studies have been carried out to understand the phenomenon of triggered seismicity including source mechanism fault geometry crustal structure earthquake processes causal relationship with reservoir water level changes and anomalous water level fluctuations in cased bore wells the present review takes stock of all such studies undertaken so far to summarise the understanding on various geo scientific issues and milestone achievements with regard to mechanism of triggered seismicity and source processes fault plane solutions commensurate with geometry of faulting source parameters seismogenic depth crustal structure and the role of reservoir water level two stage increase in seismic energy release coinciding with peaks of annual filling and draining cycle of reservoir with one month delay vis a vis spurt of moderate earthquakes m 5 due to i rapid rise in reservoir level 12 m week ii reservoir water level exceeding the previous maxima and iii duration for which high reservoir level is retained are characteristic features numerical models simulating diffusion of pore fluid pressure fronts during the filling stage of reservoir suggest stress perturbations of the order of 0 75 2 25 bar at hypocentral depth triggering earthquakes on critically stressed pre existing faults in the year 2005 a 13 station digital seismometers network became functional that characterized the distribution of epicentres in the area with increased accuracy and suggested four major seismic zones with well defined clusters scientific drilling carried out recently provide several new information regarding the subsurface geology and structure in the koyna region such as i thickness of deccan traps 933 in the koyna area and 1185 m in the warna area ii presence of granite gneiss basement directly underlying the deccan traps iii absence of infratrappean sediments and iv temperature not exceeding 150 c at hypocentral depth it is planned to establish a deep borehole observatory close to the seismic source zone for direct measurements of physical and mechanical properties of rocks pore fluid pressure hydrology thermal condition and other parameters of an intra plate active fault zone in the near field of earthquakes before during and after their occurrence results from such experiment and long term in situ monitoring of critical parameters would enhance our understanding on the mechanism of triggered earthquakes and the role of reservoir water level fluctuations

investigations related to scientific deep drilling to study reservoir triggered earthquakes at koyna india artificial water reservoir triggered earthquakes have continued at koyna in the deccan traps province india since the impoundment of the shivaji sagar reservoir in 1962 existing models to comprehend the genesis of triggered earthquakes suffer from lack of observations in the near field to investigate further scientific deep drilling and setting up a fault zone observatory at depth of 5 7 km is planned in the koyna area prior to undertaking deep drilling an exploratory phase of investigations has been launched to constrain subsurface geology structure and heat flow regime in the area that provide critical inputs for the design of the deep borehole observatory two core boreholes drilled to depths of 1 522 and 1 196 m have penetrated the deccan traps and sampled the granitic basement in the region for the first time studies on cores provide new and direct information regarding the thickness of the deccan traps the absence of infra trappean sediments and the nature of the underlying basement rocks temperatures estimated at a depth of 6 km in the area made on the basis of heat flow and thermal properties data sets do not exceed 150 c low elevation airborne gravity gradient and magnetic data sets covering 5 012 line km together with high quality magnetotelluric data at 100 stations provide both regional information about the thickness of the deccan traps and the occurrence of localized density heterogeneities and anomalous conductive zones in the vicinity of the hypocentral zone acquisition of airborne lidar data to obtain a high resolution topographic model of the region has been completed over an area of 1 064 km2 centred on the koyna seismic zone seismometers have been deployed in the granitic basement inside two boreholes and are planned in another set of six boreholes to obtain accurate hypocentral locations and constrain the disposition of fault zones

infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the xihuashan tungsten deposit jiangxi province china the xihuashan tungsten deposit jiangxi province china is a world class vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions there are two major sets of subparallel ore bearing quartz veins the ore mineral assemblage includes wolframite and molybdenite with minor amounts of arsenopyrite chalcopyrite and pyrite there are only two phase aqueous rich inclusions in wolframite but at least three major types of inclusions in quartz two or three phase co2 rich inclusions two phase pure co2 inclusions and two phase aqueous inclusions indicating boiling fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities 239 380 c 3 8 13 7 wt nacl equiv compared with those in quartz 177 329 c 0 9 8 1 wt nacl equiv these distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process enthalpy salinity plot shows a linear relationship implying mixing of different sources of fluids although boiling occurred during vein type mineralization it seems negligible for wolframite deposition mixing is the dominant mechanism of wolframite precipitation in xihuashan 34s values of the sulfides range from 1 6 to 0 1 indicative of a magmatic source of sulfur 18o values of wolframite are relatively homogeneous ranging from 4 8 to 6 3 oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite

surface heat flow and probable evolution of deccan volcanism abstract in the light of surface heat flow observations as well as other related geological and geophysical data the origin of the deccan basalts has been examined the indian lithosphere after its detachment from gondwanaland apparently traversed a rising plume at la reunion which virtually bored through the lithosphere to emerge as the deccan trap volcanism on the surface subsequent volcanic and plutonic activity appears to have continued not only up to the oligocene as is indicated by the alkaline magmatic activity observed near the junction of the three prominent features the west coast faults the narmada son tapti lineament and the cambay graben but also up to the mio pliocene as indicated by the heat flow and gravity data over the cambay graben the dyke swarms and sills which are mostly post trappean evolved from the lithosphere after the indian plate moved away from the hot spot

rock strength measurements on archaean basement granitoids recovered from scientific drilling in the active koyna seismogenic zone western india abstract reservoir triggered earthquakes have been occurring in the koyna area western india for the past five decades triaxial tests carried out on 181 core samples of archaean granitoids underlying the deccan traps provide valuable constraints on rock strength properties in the koyna seismogenic zone for the first time the data include measurements on granite gneiss granite migmatitic gneiss and mylonitised granite gneiss obtained from boreholes kbh 3 kbh 4a kbh 5 and kbh 7 located in the western and eastern margins of the seismic zone salient results are as follows i increase of rock strength with increasing confining pressure allow determination of the linearized failure envelopes from which the cohesive strength and angle of internal friction are calculated ii variable differential stresses at different depths are the manifestations of deformation partitioning in close association of fault zone s or localized fracture zones iii fractures controlled by naturally developed weak planes such as cleavage and fabric directly affect the rock strength properties but the majority of failure planes developed during triaxial tests is not consistent with the orientations of pre existing weak planes the failure planes may therefore represent other planes of weakness induced by ongoing seismic activity iv stress strain curves confirm that axial deformation is controlled by the varying intensity of pre existing shear in the granitoids viz mylonite granite gneiss and migmatitic gneiss v frequent occurrences of low magnitude earthquakes may be attributed to low and variable rock strength of the granitoids which in turn is modified by successive seismic events

location of the pilot borehole for investigations of reservoir triggered seismicity at koyna india abstract artificial water reservoir triggered earthquakes are now known to have occurred at over 120 sites globally the part played by the reservoirs in triggering is not exactly known due to lack of near field observations of triggered earthquakes koyna located near the west coast of india where triggered earthquakes have been occurring since 1962 provides an excellent site for near field observations of the target m 2 earthquakes a 6 borehole seismic network has been deployed recently in the koyna region at depths of 981 1522 m to improve the hypocenter locations during may december 2015 a total of 1039 earthquakes of m l 0 5 were located using the borehole seismic network the region is also monitored through a dense network of 23 surface broad band stations our analysis indicates a significant improvement in the estimation of absolute locations of earthquakes with errors of the order of 300 m combining both the networks based on seismicity and logistics a block of 2 2 km 2 area has been chosen for drilling the first pilot borehole of 3 km depth where m 2 earthquakes have been occurring frequently since 2005

shear wave velocity structure of the koyna warna region in western india using ambient noise correlation and surface wave dispersion abstract the koyna warna region is a premier site of reservoir triggered seismicity in the deccan volcanic province of western india in the present study shear wave velocity structure of this region down to a depth of 10 km is estimated using the ambient noise correlation technique with data from a network of 11 seismic broadband stations asymmetric green s functions are obtained that are suggestive of an anisotropic distribution of noise sources in the indian subcontinent cross correlation of continuous noise data of 12 months duration recorded on the vertical components enables computation of group velocity dispersion curves from the green s functions this is supplemented by rayleigh waves from local earthquakes which in addition to those from noise data are inverted for the shear wave velocity structure using the multiple filter technique the study reveals on an average a 0 8 km thick basaltic layer of the deccan traps with a shear wave velocity of about 3 0 km s on the eastern side of the escarpment a low velocity possibly weathered granitic layer with a velocity of 3 3 km s is found below the traps and is underlain by the granitic basement with a velocity of 3 6 km s except for the surface topographic undulation the velocity structure in this region down to 10 km is similar on either side

understanding conspicuous gravity low over the koyna warna seismogenic region maharashtra india and earthquake nucleation a paradigm shift the continued seismicity in koyna warna region of the western part of maharastra india and its relationship with subsurface structures concealed below thick volcanic sequences are studied in detail using gravity field along with newly available deep scientific drilling results this seismically active zone is marked by a large conspicuous negative gravity anomaly the causes of which are yet to be fully understood recent findings from the boreholes drilled in the koyna gupta et al in int j earth sci 104 1511 1522 2015 and killari seismic zones both of which penetrated the thick deccan volcanic cover and the underlying archean crystalline basement have motivated us to revisit the bouguer gravity field over this region using a newly developed finite element method of regional residual separation our study reveals the presence of two thick low density low velocity crustal zones below the koyna warna region the shallower one between 5 and 13 km depth and the deeper one between 35 and 43 km depth just above the moho both of these zones appear to contain mantle metasomatised and fractionated magmatic material respectively interestingly the hypocenters of all m 5 koyna earthquakes occur within the upper low velocity low density zone we also suggest high order crustal exhumation below this region which led to the removal of the entire sedimentary and granitic upper crustal column this process has brought denser mid crustal lithological facies close to the surface quaternary uplifting and movement of fault blocks along the old as well as newly created fault planes seem to be still continuing a paleo rift may have existed beneath this region below which moho temperatures 600 c and mantle heat flow 31 mw m2 are still high

waveform inversion of broad band data of local earthquakes in the koyna warna region western india summary the koyna warna region in western india is the best example of reservoir triggered seismicity the world s largest triggered earthquake of magnitude 6 3 occurred in koyna in 1967 followed by several moderate to small earthquakes ever since a digital seismograph network deployed for seismic monitoring during 2005 august to 2008 december has indicated a shift in concentration of seismicity towards south in the warna region including a new zone of seismic activity to the southwest during the observation period 13 earthquakes of magnitude 4 and greater have occurred of which 11 occurred near the warna region while only two occurred in koyna in this study we modelled broad band waveform data of six of these earthquakes near warna using waveform inversion approach initially a new velocity model was determined using a joint hypocentral determination approach that simultaneously solves for the velocity structure as well as the hypocentral parameters a trap thickness of 1 2km with a p wave velocity of 4 40kms 1 and an upper crustal layer down to 10km with a velocity of 5 96kms 1 are obtained the new model not only provides the minimum residual error for the traveltimes but consistently provides the least mismatch error in the waveform inversion of all the events performing better than any of the previously determined velocity models in general focal mechanisms of normal type with ns to nnw sse oriented fault planes are obtained for all these events that are correlated with probable faults inferred from satellite images and aeromagnetic anomalies focal depths in the range of 5 6km are obtained for earthquakes in the warna region based on the sensitivity of whole waveform inversion at local distances it is felt that joint inversion of waveform data of several earthquakes with a wider spatial distribution along with the velocity structure would help in precisely characterizing the faulting mechanism and seismogenic depth range for the koyna warna region in future