Geophysics Research Papers - Academia.edu (original) (raw)

Melt impregnated plagioclase lherzolites from the Nain mélange, central Iran, contain pyroxenes enriched and chemically zoned with Sr. Pyroxenes from the lherzolite and the clinopyroxenite seams, which have been precipitated from the... more

Melt impregnated plagioclase lherzolites from the Nain mélange, central Iran, contain pyroxenes enriched and chemically zoned with Sr. Pyroxenes from the lherzolite and the clinopyroxenite seams, which have been precipitated from the impregnating melt, show similar trace element geochemical characteristics, including a similar Sr anomaly. The associated plagioclase, precipitated from the impregnating melt, has been selectively altered to isotropic saussurite. Strontium concentration increases in the pyroxenes from the core to the rim and toward crosscutting saussurite trails in orthopyroxene porphyroclast cores. The highest Sr content (up to 10.8 ppm in clinopyroxene and 3.8 ppm in orthopyroxene) is found in the finer pyroxenes surrounded by thicker saussurite layers. The Sr enrichment within pyroxenes is neither caused by metasomatism nor modified by fluids involved in hydrothermal alteration because pyroxenes are extremely depleted in fluid-mobile and light rare earth elements. Also, Sr enrichment cannot be related to the melt impregnation, since the Sr supply from the impregnating melt was consumed by plagioclase crystallization. The Sr enrichment in the pyroxene postdates the melt impregnation and is due to the relatively high-temperature (375°C-850°C) of saussuritization, that is, the breakdown of plagioclase. Plagioclase decomposition has released appreciable amounts of Sr to enrich adjacent pyroxenes. Saussurite shows significantly lower Sr contents than the plagioclase. Sr enrichment in peridotite pyroxenes, which is ascribed primarily to the metasomatism of slab-derived fluids, should be treated carefully, particularly when altered plagioclase is present.

Volcano monitoring aims at the recognition of changes in instrumentally observable parameters before hazardous activity in order to alert governmental authorities. Among these parameters seismic data in general and volcanic tremor in... more

Volcano monitoring aims at the recognition of changes in instrumentally observable parameters before hazardous activity in order to alert governmental authorities. Among these parameters seismic data in general and volcanic tremor in particular play a key role. Recent major explosive eruptions such as Okmok (Aleutians) and Chaitén (Chile) in 2008 and numerous smaller events at Mt Etna (Italy), have shown that the period of premonitory seismic activity can be short (only a few hours), which entails the necessity of effective automatic data processing near on-line. Here we present a synoptic pattern classification analysis based on Self Organizing Maps and Fuzzy Cluster Analysis which is applied to volcanic tremor data recorded during a series of paroxysmal eruptive episodes and a flank eruption at Etna in 2007-2008. In total, eight episodes were analyzed; in six of these significant changes in the dynamic regime of the volcano were detected up to 9 h prior to the onset of eruptive activity, and long before changes in volcanic tremor amplitude and spectral content became evident in classical analysis. In two cases, the state transition was b 1 h before the onset of eruptive activity, which we interpret as evidence for very rapid magma ascent through an open conduit. We further detected twenty failed paroxysms, that is episodes of volcanic unrest that did not culminate in eruptive activity, between March and April 2007. As the application of the software for this synoptic pattern classification is straightforward and requires only moderate computational resources, it was possible to exploit it in an on-line application, which was tested and now is in use at the Istituto Nazionale di Geofisica e Vulcanologia in Catania for the monitoring of Etna. We believe that the pattern classification presented here may become a powerful addition to the repertoire of volcano monitoring tools and early warning techniques worldwide.

This paper describes the analysis of L-band radiometric measurement data gathered with the synthetic aperture radiometer HUT-2D during several ground-based and airborne measurement campaigns. The radiometric data are analyzed from the... more

This paper describes the analysis of L-band radiometric measurement data gathered with the synthetic aperture radiometer HUT-2D during several ground-based and airborne measurement campaigns. The radiometric data are analyzed from the instrument's performance point of view, aiming to verify the theoretical performance of an instrument of this kind and to assess the performance of the HUT-2D radiometer system in particular. The data sets considered for the study consist of measurements of well-known natural targets, such as cosmic background radiation, and measurements of pure water scenes, the brightness temperature of which is possible to model based on in situ measurements. We define four figures of merit, which are applicable for synthetic aperture radiometers. These are radiometric resolution, image bias, pixel-to-pixel random error, and temporal stability. Then, we use the selected data sets to assess these in the case of HUT-2D. The experimental results are discussed and compared to the theoretical values, where applicable. Also, we discuss possibilities to improve the presented performance. The main results of this paper are the consolidated performance parameters of the HUT-2D instrument. We study and discuss the properties of the error components related to the technology in a general level, and study the scalability of the errors as a function of the measured targets. In particular, the stability of the direction-dependent error component is pointed out, and a mitigation guideline is proposed.

The seismicity depth distribution in the central and southern East African Rift System (EARS) is investigated using available catalogs from local, regional and global networks. We select well-determined events and make a re-assessment of... more

The seismicity depth distribution in the central and southern East African Rift System (EARS) is investigated using available catalogs from local, regional and global networks. We select well-determined events and make a re-assessment of these catalogs, including a relocation of 40 events and, where necessary, a declustering. About 560 events are finally used for determining foci depth distribution within 6 areas of the EARS. Assuming that short-term deformation expressed by seismicity reflects the long-term mechanical properties of the lithosphere, we build yield strength envelopes from seismicity depth distribution. Using brittle and ductile laws, we predict the strength percentage spaced every 5 km (or sometimes 2 km) in the crust, for a given composition and a specific geotherm, and constrain it with the relative abundance of seismicity. Results of this modeling indicate significant local and regional variations of the thermomechanical properties of the lithosphere which are broadly consistent with previous studies based on independent modelings. In order to explain relatively deep earthquakes, a highly resistant, mafic lower crust is generally required. We also find evidence for changes in the strength magnitude and in the depth of the brittle-ductile transitions which are clearly correlated to tectonic provinces, characterized by contrasted thermal gradients and basement types. A clear N-S increase and deepening of the peak strength level is evidenced along the eastern branch of the EARS, following a consistent southward migration of rifting sincẽ 8 Ma. We also detect the presence of a decoupling layer in the Kenya rift, which suggests persisting influences of the deep crustal structures (Archaean and Proterozoic) on the behavior of the extending crust. More generally, our results suggest that seismicity peaks and cut-off depths may provide good proxies for bracketing the brittle-ductile transitions within the continental crust.

The present study examines the process of how tropospheric air enters the stratosphere, particularly in association with tropical mesoscale convective systems (TMCS) which are considered to be one of the causative mechanisms for the... more

The present study examines the process of how tropospheric air enters the stratosphere, particularly in association with tropical mesoscale convective systems (TMCS) which are considered to be one of the causative mechanisms for the observation of extremely low tropopause temperature over the tropics. The association between the phenomena of convection and the observation of extreme low tropopause temperature events is, therefore, examined over the Asian monsoon region using data from multiple platforms. Satellite observations show that the area of low outgoing long wave radiation (OLR), which is a proxy for the enhanced convection, is embedded with high altitude clouds top temperatures (≤193 K). A detailed analysis of OLR and 100 hPa temperature shows that both are modulated by westward propagating Rossby waves with a period of ∼15 days, indicating a close linkage between them. The process by which the tropospheric air enters the stratosphere may, in turn, be determined by how the areas of convection and low tropopause temperature (LTT) i.e. T ≤ 191 K are spatially located. In this context, the relative spatial distribution of low OLR and LTT areas is examined. Though, the locations of low OLR and LTT are noticed in the same broad area, the two do not always overlap, except for partial overlap in some cases. When there are multiple low OLR areas, the LTT area generally appears in between the low OLR areas. Implications of these observations are also discussed. The present analysis also shows that the horizontal mean winds have a role in the spatial distribution of low OLR and LTT.

The Timor-Tanimbar region constitutes part of the non-volcanic outer Banda Arc of Eastern Indonesia. Here, the world's youngest 'A'-type high-pressure metamorphic belt crops out with different stages of evolution. Whereas an advanced... more

The Timor-Tanimbar region constitutes part of the non-volcanic outer Banda Arc of Eastern Indonesia. Here, the world's youngest 'A'-type high-pressure metamorphic belt crops out with different stages of evolution. Whereas an advanced domal uplift stage is seen in Timor island, the high-pressure (HP) metamorphic belt is still in the first stage of tectonic extrusion on the eastern small islands of Kisar, Leti, Moa, Sermata and Laibobar. The metamorphic rocks on Leti are among the best exposed in the islands. They are tectonically juxtaposed against overlying ultramafic rocks and underlying unmetamorphosed continental shelf sediments, bound by normal and reverse faults, respectively. The Leti metapelites display four progressive metamorphic zones: chlorite-biotite, garnet, chloritoid-staurolite and kyanite zones, with increasing grade. Zonation in Leti metabasite unit is comparable, and progressively changes from blueschist-greenschist transition (BS/GS), through epidote-amphibolite (EA), to amphibolite (AM) facies, with increasing grade. The highest-grade metapelites and metabasites occupy structurally intermediate levels.

Within the eastern Himalayan syntaxis, carbonatite-like dykes occur in granulite facies gneisses of the Greater Himalayan Crystallines. Most dykes are dolomitic and are associated with scapolite-bearing hornblendite and glimmerite, which... more

Within the eastern Himalayan syntaxis, carbonatite-like dykes occur in granulite facies gneisses of the Greater Himalayan Crystallines. Most dykes are dolomitic and are associated with scapolite-bearing hornblendite and glimmerite, which are separated from the country rocks by a selvage of altered rocks containing minerals such as diopside, tremolite, K-feldspar, albite, and calcite. Only a few dykes are calcitic with alteration halos containing wollastonite, calcite, anorthite, diopside, and scapolite. Dolomitic dykes as wide as several tens of metres contain irregular xenoliths of granulitic gneiss.

The Mesozoic southern branch of the Neo-Tethys Ocean was located between the Arabian shield and the Sanandaj-Sirjan continental block of Iran. The Kermanshah ophiolitic complex crops out in the Main Zagros Thrust Zone in Iran and consists... more

The Mesozoic southern branch of the Neo-Tethys Ocean was located between the Arabian shield and the Sanandaj-Sirjan continental block of Iran. The Kermanshah ophiolitic complex crops out in the Main Zagros Thrust Zone in Iran and consists of several rock associations, which record the geodynamic evolution of this ocean. In particular, the ophiolitic rocks that record the early stage of this oceanic evolution are represented by mantle metalherzolites, metagabbros and crosscutting metabasaltic dykes, as well as by basaltic pillow lavas and dykes. Mineral chemistry and whole-rock geochemistry of the metalherzolites show that they represent portions of exhumed sub-continental mantle. Four groups of rock can be recognized within the metagabbro and volcanic/subvolcanic sequences, based on many geochemical indicators and Sr-Nd isotopic data. They are: (1) metagabbros and metadykes with a N-MORB signature; (2) alkaline basalts and trachybasalts with ocean-island basalt (OIB) affinity; (3) rocks showing plume-type MORB (P-MORB) affinity; and (4) rocks showing enriched-type MORB (E-MORB) affinity. Metagabbros and metadykes show either low or high Sm/Yb ratios, which point to a genesis from partial melting of a pure depleted MORB mantle (DMM) source or a DMM source bearing garnet-pyroxenite relics, respectively. All volcanic and subvolcanic rock-types have variable, but generally high La/Yb, Sm/Yb, Th/Yb, Ta/Yb and Zr/Y ratios, and low Zr/Nb ratios. These features coupled with relatively low 143 Nd/ 144 Nd ratios and high 87 Sr/ 86 Sr indicate that the alkaline rocks were generated from an enriched, OIB-type (plume-type?) mantle source, whereas P-and E-MORB rocks can be interpreted as the product of variable interaction between depleted MORB-type asthenosphere and OIB-type material. We propose a tectono-magmatic model that can explain the different rock associations cropping out in the Kermanshah ophiolites involving a type of rifted margin that is intermediate between the amagmatic Iberia/Ligurian Tethys type and the magmatic, plume-influenced East Greenland type. This model presupposes that the Sanandaj-Sirjan block was rifted from the northern margin of Arabia through passive extension, which led to the exhumation of the sub-continental mantle now represented by the metalherzolites. Meanwhile, the asthenosphere upwelling associated with the partial melting of a heterogeneous mantle source locally bearing garnet-pyroxenite relics allowed the formation of both low and high Sm/Yb N-MORB-type metagabbros and metadykes at the continent-ocean transition zone. This model is similar to the model proposed for the Ligurian Tethys. But, in contrast with the Ligurian Tethys model, extension was also associated with volcanism characterized by a marked influence of OIB-type components linked to the uprising of MORB-type, depleted asthenospheric mantle. If so, the Kermanshah ophiolites represent a particular type of continental margin ophiolite, comprising a combination of continental margin-and plume-type ophiolites.

New age data on detrital zircons and micas are presented from key units within the Neoproterozoic Katanga Supergroup, which hosts the major stratiform Cu-Co deposits of the Central African Copperbelt. Detrital zircon ages indicate a... more

New age data on detrital zircons and micas are presented from key units within the Neoproterozoic Katanga Supergroup, which hosts the major stratiform Cu-Co deposits of the Central African Copperbelt. Detrital zircon ages indicate a mainly Palaeoproterozoic (between 2081 ± 28 and 1836 ± 26 Ma) provenance for the Katanga basin, derived from the Lufubu Metamorphic Complex of the Kafue Anticline and the Bangweulu Block to the north of the outcrop belt. Detrital zircons and clasts from the Grand Conglomerat glacial diamictite indicate a source from the Palaeoproterozoic metavolcanic porphyries and granitoids of Luina Dome region, which was a basement high during Nguba Group deposition. Minor zircons of Mesoproterozoic age may have been derived from the Kibaran belt. Finally, 40 Ar/ 39 Ar age data from detrital muscovites from Biano Group siltstones give a maximum age of sedimentation of 573 Ma, strongly supporting previous models that the Biano Group was deposited in a foreland basin of the Lufilian Orogen.

Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and mankind in general for many years. The study of thunderstorms has rapidly advanced during the past century and many... more

Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and mankind in general for many years. The study of thunderstorms has rapidly advanced during the past century and many efforts have been made towards understanding lightning, thunderstorms and their consequences. Recent observations of optical phenomena above an active lightning discharge along with the availability of modern technology both for data collection and data analysis have renewed interest in the field of thunderstorms and their consequences in the biosphere. In this paper, we review the electrification processes of a thunderstorm, lightning processes and their association with global electric circuit and climate. The upward lightning discharge can cause sprites, elves, jets, etc. which are together called transient luminous events.

We present a new method of regularization of seismic data using the finite offset common reflection source (FOCRS) traveltime approximation. This method fits curves of common reflection source to the reflection events and... more

We present a new method of regularization of seismic
data using the finite offset common reflection source (FOCRS) traveltime approximation. This method fits curves
of common reflection source to the reflection events and
stacks all the amplitudes in a given aperture. The stacked
amplitude, afterwards, is allocated to the time coordinate
in the trace to be interpolated. We applied this method to
three synthetic velocity models and the results showed
the capability for regularizing converted seismic waves in
stratified medium.

Object-based image analysis (OBIA) is a method of assessing remote sensing data that uses morphometric and spectral parameters simultaneously to identify features in remote sensing imagery. Over the past 10-15 years, OBIA methods have... more

Object-based image analysis (OBIA) is a method of assessing remote sensing data that uses morphometric and spectral parameters simultaneously to identify features in remote sensing imagery. Over the past 10-15 years, OBIA methods have been introduced to detect archaeological features. Improvements in accuracy have been attained by using a greater number of morphometric variables and multiple scales of analysis. This article highlights the developments that have occurred in the application of OBIA within archaeology and argues that OBIA is both a useful and necessary tool for archaeological research. Additionally, I discuss future research paths using this method. Some of the suggestions put forth here include: pushing for multifaceted research designs utilizing OBIA and manual interpretation, using OBIA methods for directly studying landscape settlement patterns, and increasing data sharing of methods between researchers.

During the last two years three very similar reference books on mineral species have been published, the MineralReference Manualby E.H. Nickel and M.C. Nichols being one of them. The others are:

This paper describes the successful application of amplitude-versus-angle ͑AVA͒ inversion of prestack-seismic amplitude data to detect and delineate deepwater hydrocarbon reservoirs in the central Gulf of Mexico. Detailed AVA fluid/... more

This paper describes the successful application of amplitude-versus-angle ͑AVA͒ inversion of prestack-seismic amplitude data to detect and delineate deepwater hydrocarbon reservoirs in the central Gulf of Mexico. Detailed AVA fluid/ lithology sensitivity analysis was conducted to assess the nature of AVA effects in the study area based on well-log data. Standard techniques such as crossplot analysis, Biot-Gassmann fluid substitution, AVA reflectivity modeling, and numerical simulation of synthetic gathers were part of the AVA sensitivity analysis.

Twenty years of continuous Earth observation by satellite SAR have resulted in numerous new insights into active volcanism, including a better understanding of subsurface magma storage and transport, deposition of volcanic materials on... more

Twenty years of continuous Earth observation by satellite SAR have resulted in numerous new insights into active volcanism, including a better understanding of subsurface magma storage and transport, deposition of volcanic materials on the surface, and the structure and development of volcanic edifices. This massive archive of data has resulted in fundamental leaps in our understanding of how volcanoes work - for example, identifying magma accumulation at supposedly quiescent volcanoes, even in remote areas or in the absence of ground-based data. In addition, global compilations of volcanic activity facilitate comparison of deformation behavior between different volcanic arcs and statistical evaluation of the strong link between deformation and eruption. SAR data are also increasingly used in timely hazard evaluation thanks to decreases in data latency and growth in processing and analysis techniques. The existing archive of SAR imagery is on the cusp of being enhanced by a new gene...

A 727 m thick sequence of the Lower and Mid Palaeozoic in Satun province, south peninsular Thailand is represented by a continuous succession of deeper water carbonates and clastic rocks ranging from the Caradoc to the Silurian,... more

A 727 m thick sequence of the Lower and Mid Palaeozoic in Satun province, south peninsular Thailand is represented by a continuous succession of deeper water carbonates and clastic rocks ranging from the Caradoc to the Silurian, conformably overlain by the shallower water carbonates and clastic rocks of the

A Lower Devonian (Emsian) tentaculite fauna including Nowakia acuaria [Richer, R., 1854. Thüringische Tentaculiten. Zeitschr. Deutsch. Geol. Gesellsch. 6, 275-290] occurs in black shale in the basal part of a siliciclastic sequence... more

A Lower Devonian (Emsian) tentaculite fauna including Nowakia acuaria [Richer, R., 1854. Thüringische Tentaculiten. Zeitschr. Deutsch. Geol. Gesellsch. 6, 275-290] occurs in black shale in the basal part of a siliciclastic sequence exposed north of Satun, southern peninsular Thailand. Similar tentaculite beds with Nowakia have been reported from several areas in the Fang, Sri Sawat, and Trang areas of Thailand, the Langkawi Islands and the Mahang-Baling areas of Malaysia. The depositional environments in which the tentaculite-bearing black shale accumulated extended from modern northern Thailand to northwestern Malaysia during the Early Devonian (Emsian). q

Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field... more

Over the last decades, numerous studies have emphasized the role of serpentinites in the subduction zone geodynamics. Their presence and role in subduction environments are recognized through geophysical, geochemical and field observations of modern and ancient subduction zones and large amounts of geochemical database of serpentinites have been created. Here, we present a review of the geochemistry of serpentinites, based on the compilation of~900 geochemical data of abyssal, mantle wedge and exhumed serpentinites after subduction. The aim was to better understand the geochemical evolution of these rocks during their subduction as well as their impact in the global geochemical cycle. When studying serpentinites, it is essential to determine their protoliths and their geological history before serpentinization. The geochemical data of serpentinites shows little mobility of compatible and rare earth elements (REE) at the scale of hand-specimen during their serpentinization. Thus, REE abundance can be used to identify the protolith for serpentinites, as well as magmatic processes such as melt/rock interactions before serpentinization. In the case of subducted serpentinites, the interpretation of trace element data is difficult due to the enrichments of light REE, independent of the nature of the protolith. We propose that enrichments are probably not related to serpentinization itself, but mostly due to (sedimentary-derived) fluid/rock interactions within the subduction channel after the serpentinization. It is also possible that the enrichment reflects the geochemical signature of the mantle protolith itself which could derive from the less refractory continental lithosphere exhumed at the ocean-continent transition. Additionally, during the last ten years, numerous analyses have been carried out, notably using in situ approaches, to better constrain the behavior of fluid-mobile elements (FME; e.g. B, Li, Cl, As, Sb, U, Th, Sr) incorporated in serpentine phases. The abundance of these elements provides information related to the fluid/rock interactions during serpentinization and the behavior of FME, from their incorporation to their gradual release during subduction. Serpentinites are considered as a reservoir of the FME in subduction zones and their role, notably on arc magma composition, is underestimated presently in the global geochemical cycle.

Four sets of thin-section scale, Mode I (open mode), cemented microfractures are present in sandstone from the Eocene Misoa Formation, Maracaibo basin, Venezuela. The first set of microfractures is intragranular (F1), formed early during... more

Four sets of thin-section scale, Mode I (open mode), cemented microfractures are present in sandstone from the Eocene Misoa Formation, Maracaibo basin, Venezuela. The first set of microfractures is intragranular (F1), formed early during compaction and are filled with quartz cement precipitated at temperatures equal to or higher than 100 8C. The second set of microfractures (F2) is cemented by bituminite-pyrite, formed at temperatures between 60 and 100 8C, and are associated with kerogen maturation and hydrocarbon migration from underlying overpressured source rocks. The third set of microfractures (F3) is fully cemented by either quartz cement or calcite cement. The former has fluid inclusion homogenization temperatures between 149 and 175 8C. These temperatures are mostly higher than maximum burial temperatures (~160 8C), suggesting that upward flow, caused by a pressure gradient, transported silica vertically which crystallized into the fractures. Upward decompression may have also caused a P CO 2 drop, which, at constant temperature, allowed simultaneous carbonate precipitation into the third microfracture set. The fourth set of thin-section scale microfractures (F4) is open or partially cemented by sideritehematite and other iron oxides. The presence of hematite and iron oxides in microfractures is evidence for oxidizing conditions that may be associated with the uplift of the Misoa formation. In order to time and place constraints on the depth of formation of the fourth set of microfractures, we have coupled published quartz cementation kinetic algorithms with uniaxial strain equations and determined if, in fact, they could be associated with the uplift of the formation. Our results suggest that thermoelastic contraction, caused by the formation's uplift, erosion, and consequent cooling is a feasible mechanism for the origin of the last fracture set. Hence, we infer that meteoric water invasion into the fractures, at the end of the uplift, cause the precipitation of oxides and the transformation of siderite to hematite. D

A study has been done in Luvuvhu Catchment to develop a framework for effective community participation in water quality monitoring and management. Community participation and involvement in development has since the 1970s gathered... more

A study has been done in Luvuvhu Catchment to develop a framework for effective community participation in water quality monitoring and management. Community participation and involvement in development has since the 1970s gathered momentum among the non-governmental organisations (NGOs) fraternity but has never gained clear status with Governments world over. In South Africa the policy and legal frameworks for community consultation, involvement and participation are clearly spelt out on paper starting with the country's constitution. The division of the country into Water Management Areas (WMA) and the formation of Catchment Management Agencies (CMA), Water User Associations (WUAs) for example, was meant to increase participation of stakeholders including communities in the management of water resources. These efforts have not translated into effective participation by local communities in the management of water resources because there is no link between the national water quality management frameworks and community based development structures.

Monografies d'Ullastret 3, Museu d'Arqueologia de Catalunya, Ullastret, 2017

U-Pb SHRIMP zircon age data, together with geochemical analyses

The Nile deep turbiditic system displays many fluid-releasing structures on the seabed: mud volcanoes reassembling small cones (100 -900 m in diameter), mud pies (5 km in diameter), and pockmarks. The cones are restricted to the western... more

The Nile deep turbiditic system displays many fluid-releasing structures on the seabed: mud volcanoes reassembling small cones (100 -900 m in diameter), mud pies (5 km in diameter), and pockmarks. The cones are restricted to the western province. Mud 'pies' delineate a belt of apparently very active gas chimneys along the upper continental slope. Pockmarks are associated either with strongly destabilized sedimentary masses or with gas chimneys. We distinguish five main controlling parameters interacting in fluid release locations:

An adaptive and fast constant false alarm rate (CFAR) algorithm based on automatic censoring (AC) is proposed for target detection in high-resolution synthetic aperture radar (SAR) images. First, an adaptive global threshold is selected... more

An adaptive and fast constant false alarm rate (CFAR) algorithm based on automatic censoring (AC) is proposed for target detection in high-resolution synthetic aperture radar (SAR) images. First, an adaptive global threshold is selected to obtain an index matrix which labels whether each pixel of the image is a potential target pixel or not. Second, by using the index matrix, the clutter environment can be determined adaptively to prescreen the clutter pixels in the sliding window used for detecting. The G 0 distribution, which can model multilook SAR images within an extensive range of degree of homogeneity, is adopted as the statistical model of clutter in this paper. With the introduction of AC, the proposed algorithm gains good CFAR detection performance for homogeneous regions, clutter edge, and multitarget situations. Meanwhile, the corresponding fast algorithm greatly reduces the computational load. Finally, target clustering is implemented to obtain more accurate target regions. According to the theoretical performance analysis and the experiment results of typical real SAR images, the proposed algorithm is shown to be of good performance and strong practicability.

Large compressional earthquakes in the upper crust, and even larger plate-boundary earthquakes in subduction zones, produce surface deformation recorded by displacements on reverse or thrust faults, by growth of surface folds, and by... more

Large compressional earthquakes in the upper crust, and even larger plate-boundary earthquakes in subduction zones, produce surface deformation recorded by displacements on reverse or thrust faults, by growth of surface folds, and by changes in the elevation of the land surface. Study of such stratigraphic and geomorphic features yields information about the size and recurrence of large earthquakes that is not available from historic sources in many regions. Coupled with regional-scale knowledge about structure, geophysics, and landscape development, such data allow characterization of seismic fault source zones in regions dominated by compressional tectonics (Chapter 9, See Book's Companion website).

Telluric currents are natural electrical phenomena in the Earth or its bodies of water. The strongest electric currents are related to lightning phenomena or space weather. Earth electricity can cause damage to structures, and may be... more

Telluric currents are natural electrical phenomena in the Earth or its bodies of water. The strongest electric currents are related to lightning phenomena or space weather. Earth electricity can cause damage to structures, and may be useful for earthquake forecasting and other applications. Thirty-two distinct mechanisms that cause Earth electricity are
described, and a broad selection of current research is highlighted.

The transition from mechanical thinning toward focused magmatic intrusion during continental rifting is poorly constrained; the tectonically active Main Ethiopian Rift (MER) provides an ideal study locale to address this issue. The... more

The transition from mechanical thinning toward focused magmatic intrusion during continental rifting is poorly constrained; the tectonically active Main Ethiopian Rift (MER) provides an ideal study locale to address this issue. The presence of linear magmatic-tectonic belts in the relatively immature central MER may indicate that the transition from mechanical to magmatic rifting is more spatially distributed and temporally protracted than has previously been assumed. Here we examine lava geochemistry and vent distribution of a Pliocene-Quaternary linear magmatic chain along the western margin of the central MER-the Akaki Magmatic Zone. Our results show limited variability in parental magma that evolve in a complex polybaric fractionation system that has not changed significantly over the past 3 Ma. Our results suggest the following: (1) channeling of plume material and the localization of shear-or topography-induced porosity modulates melt intrusion into the continental lithosphere.

A revised kinematic model is proposed for the Neogene tectono-magmatic development of the North Tanzanian Divergence where the axial valley in S Kenya splits southwards into a wide diverging pattern of block faulting in association with... more

A revised kinematic model is proposed for the Neogene tectono-magmatic development of the North Tanzanian Divergence where the axial valley in S Kenya splits southwards into a wide diverging pattern of block faulting in association with the disappearance of volcanism. Propagation of rifting along the S Kenya proto-rift during the last 8 Ma is first assumed to have operated by linkage of discrete magmatic cells as far S as the Ngorongoro-Kilimanjaro transverse volcanic belt that follows the margin of cratonic blocks in N Tanzania. Strain is believed to have nucleated throughout the thermally-weakened lithosphere in the transverse volcanic belt that might have later linked the S Kenya and N Tanzania rift segments with marked structural changes along-strike. The North Tanzanian Divergence is now regarded as a two-armed rift pattern involving:

Across the globe, the mineral industry is seeking technology to improve exploration efficiency at depth and to help design safer and more productive mines. Seismic methods are increasingly used by this industry for a wide range of... more

Across the globe, the mineral industry is seeking technology to improve exploration efficiency at depth and to help design safer and more productive mines. Seismic methods are increasingly used by this industry for a wide range of commodities including base metals, uranium, diamonds, and precious metals. Seismic methods provide high-resolution images of geologic structures hosting mineral deposits and, in a few cases, can be used for direct targeting of mineral deposits. Applications are not limited to only surface seismic surveys, but also include borehole seismic methods such as VSP and crosshole imaging. To date, tens of 2D and 3D surface seismic surveys have been acquired in Canada, Europe, Australia, and South Africa (see Malehmir et al., 2012) to help in targeting mineral deposits at depth or for designing deep mines. The steadily increasing usage of reflection seismic methods demonstrates that they are finally becoming recognized and established within the mining sector. This brings new opportunities for geophysicists, but also new challenges. Some of these challenges and opportunities are presented and discussed in the special section. This special issue contains a wide range of topics, from petrophysical studies to data acquisition, processing and imaging, as well as 2D and 3D seismic modeling of mineral deposits and their host-rock structures. Papers from both industry and academia are presented, which illustrate the importance of seismic methods not only in the hydrocarbon industry, but also in the mineral industry. Malehmir et al. review important contributions that have been made in developing seismic techniques for the mining industry with focus on four main regions: Australia, Europe, Canada, and South Africa. A wide range of case studies are covered including some that are published in the special section accompanying this article, from surface to borehole seismic methods as well as petrophysical data and seismic modeling of mineral deposits.

Due to high metal prices and increased difficulties in finding shallower deposits, the exploration for and exploitation of mineral resources is expected to move to greater depths. Consequently, seismic methods will become a more important... more

Due to high metal prices and increased difficulties in finding shallower deposits, the exploration for and exploitation of mineral resources is expected to move to greater depths. Consequently, seismic methods will become a more important tool to help unravel structures hosting mineral deposits at great depth for mine planning and exploration. These methods also can be used with varying degrees of success to directly target mineral deposits at depth. We review important contributions that have been made in developing these techniques for the mining industry with focus on four main regions: Australia, Europe, Canada, and South Africa. A wide range of case studies are covered, including some that are published in the special issue accompanying this article, from surface to borehole seismic methods, as well as petrophysical data and seismic modeling of mineral deposits. At present, high-resolution 2D surveys mostly are performed in mining areas, but there is a general increasing trend in the use of 3D seismic methods, especially in mature mining camps.

Jones, I., Williams, D., Wiliams, S., Carruthers, W., Madgwick, R. and Young, T. 2018. Early medieval enclosure at Glanfred, near Llandre, Ceredigion. Archaeologia Cambrensis 167: 221-243. Geophysical survey and small-scale trial... more

In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10-20 Km, a radiometric resolution of 1K and a revisit time of 1-3 days... more

In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10-20 Km, a radiometric resolution of 1K and a revisit time of 1-3 days [1]. Compared to total power radiometers aperture synthesis interferometric radiometers are technologically attractive because of their reduced mass and hardware requirements. In this field it should be mentioned the one-dimensional (1-D) linear interferometer ESTAR developed by NASA [2] and MIRAS a two-dimensional (2-D) Y-shaped interferometer currently under study by European Space Agency (ESA) [3]. Interferometer radiometers measure the correlation between pairs of nondirective antennas. Each complex correlation is a sample of the "visibility" function which, in the ideal case, is the spatial Fourier transform of the brightness temperature distribution. Since most receiver phase and amplitude errors can be hardware calibrated, Fourier based iterative inversion methods will be useful when antenna errors are small, their radiation voltage patterns are not too different, and mutual coupling is small. In order to minimize on-board hardware requirements-antennas, receivers and correlators-the choice of the interferometer array shape is of great importance since it determines the (u; v) sampling strategy and the minimum number of visibility samples required for a determined aliasing level. In this sense, Y-shaped and triangularshaped arrays with equally spaced antennas are optimal. The main contribution of this paper is a technique that allows us to process the visibility samples over the hexagonal sampling grids given by Y-shaped and triangular-shaped arrays with standard rectangular FFT routines. Since no interpolation processes are involved, the risk of induced artifacts in the recovered brightness temperature over the wide field of view required in Earth observation missions is minimized and signal to noise ratio (SNR) is preserved.

Abstract—In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10–20 Km, a radiometric resolution of 1K and a revisit time of... more

Abstract—In Earth observation programs there is a need of passive low frequency (L-band) measurements to monitor soil moisture and ocean salinity with high spatial resolution 10–20 Km, a radiometric resolution of 1K and a revisit time of 1–3 days [1]. Compared to total power radiometers ...

Due to high metal prices and increased difficulties in finding shallower deposits, the exploration for and exploitation of mineral resources is expected to move to greater depths. Consequently, seismic methods will become a more important... more

Due to high metal prices and increased difficulties in finding shallower deposits, the exploration for and exploitation of mineral resources is expected to move to greater depths. Consequently, seismic methods will become a more important tool to help unravel structures hosting mineral deposits at great depth for mine planning and exploration. These methods also can be used with varying degrees of success to directly target mineral deposits at depth. We review important contributions that have been made in developing these techniques for the mining industry with focus on four main regions: Australia, Europe, Canada, and South Africa. A wide range of case studies are covered, including some that are published in the special issue accompanying this article, from surface to borehole seismic methods, as well as petrophysical data and seismic modeling of mineral deposits. At present, high-resolution 2D surveys mostly are performed in mining areas, but there is a general increasing trend in the use of 3D seismic methods, especially in mature mining camps.

Three kilns and a collection of baked bricks from Italian archaeological sites have been studied for archaeointensity determination using the Thellier method as modified by Coe. All sites are dated based on archaeological information and... more

Three kilns and a collection of baked bricks from Italian archaeological sites have been studied for archaeointensity determination using the Thellier method as modified by Coe. All sites are dated based on archaeological information and their ages range from 500 to 800 AD and 1500 to 1700 AD. Rock magnetic studies identify magnetite, Ti- magnetite and hematite as the main magnetic minerals, and magnetic susceptibility versus temperature shows a good thermal stability of the samples. The intensity results have been corrected for anisotropy of the thermoremanent magnetization and cooling rate effects. The new data together with 136 previously published results are used to estimate the variation of the Earth's magnetic field over the past three millennia. The time distribution of the Italian absolute intensity data is irregular with the majority of determinations concentrated during the last four centuries, while older periods are very poorly covered. Most of the data come from vo...

Tsunami-like sea level oscillations recently recorded by tide gauges located at offshore, as well as sheltered, sites along the coasts of British Columbia (Canada) and Washington State (USA) are identified as meteorological tsunamis. The... more

Tsunami-like sea level oscillations recently recorded by tide gauges located at offshore, as well as sheltered, sites along the coasts of British Columbia (Canada) and Washington State (USA) are identified as meteorological tsunamis. The events resemble seismically generated tsunamis but have an atmospheric, rather than seismic, origin. The event of 9 December 2005 was sufficiently strong to trigger an automatic tsunami alarm, while other events generated oscillations in several ports that were potentially strong enough to cause damage to marine craft. Analysis of coincident 1-min sea level data and high-frequency atmospheric pressure data confirms that the events originated with atmospheric pressure jumps and trains of atmospheric gravity waves with amplitudes of 1.5-3 hPa. The pronounced events of 13 July 2007 and 26 February 2008 are examined in detail. Findings reveal that the first atmospheric pressure event had a propagation speed of 24.7 m/s and an azimuth of 352°; the second event had a speed of 30.6 m/s and an azimuth of 60°. These speeds and directions are in close agreement with high-altitude geostrophic winds (the jet stream) indicating that the atmospheric disturbances generating the tsunami-like sea level oscillations are likely wind-transported perturbations rather than freely propagating atmospheric gravity waves.

The SEG Women's Network invites you to attend its Networking Breakfast at the upcoming SEG Annual Meeting in Denver, Colorado, at 8:30 to 11:00 a.m. on 29 October. This year, the program will enlist four panelists: Sally Zinke, SEG... more

The SEG Women's Network invites you to attend its Networking Breakfast at the upcoming SEG Annual Meeting in Denver, Colorado, at 8:30 to 11:00 a.m. on 29 October. This year, the program will enlist four panelists: Sally Zinke, SEG President, 2000; Allison Malcolm, SEG Clarence Karcher Award winner, 2012; Louise Pellerin, SEG Life Membership Award winner, 2014; and Sue Webb, SEG Outstanding Educator Award winner, 2014. They will describe their own journeys of success before opening the floor to a facilitated discussion with questions from the audience.