Active Geothermal Areas Research Articles

Spatial mapping and monitoring thermal anomaly and radiative heat flux using Landsat-8 thermal infrared data – A case study of Lamurde hot spring, upper part of Benue trough, Nigeria

The upper Benue trough, northeastern Nigeria is characterized by prominent geologic and tectonic features of diverse scientific and economic interest. Lamurde hot spring is located within one of several deformational structures of the trough; the Lamurde anticline. In this work, we assessed the geothermal energy potential of the area using the Thermal Infra-Red (TIR) band of Landsat-8 data. We used four datasets representing the four seasons of the year to retrieve the Land Surface Temperature (LST) by converting the pixel digital numbers into LST based on the single-channel algorithm. We also used the retrieved LST to spatially map Radiative Heat Flux (RHF) based on the Stefan-Boltzmann radiation law. We validated the results by comparing the Landsat TIR-retrieved LST with MODIS LST product of the same area using a cross-validation technique. The results indicate a reliable fitting coefficient (R2 = 0.801) and Root Mean Square Error RMSE value of 0.756 K. Although significant seasonal variation of both LST and RHF was observed, the rock outcrops associated with the hot spring high surface temperature and heat loss anomalies for all seasons of the year. Peak LST values of 43.7 °C, 35.6 °C, 29.4 °C, and 27.5 °C were respectively recorded in January, April, July, and October from the active thermal area. The average values of RHF obtained from the active thermal area are 11.78, Wm−2, 10.76 Wm−2, 1.22 Wm−2 and 0.168 Wm−2 for January, April, July and October respectively. These are much higher than the global continental value. Comparison with known active geothermal areas from different parts of the world indicates that the area has significantly high surface geothermal parameter indicators.

Geothermal resources prospecting using magnetotelluric and magnetic methods at Al Ain AlSukhuna-Al Galala Albahariya area, Gulf of Suez, Egypt

Recently, several urban and service development projects were carried out at the “City of Al-Galala Mountain”, along the Egyptian Gulf of Suez, between Al Ain Al-Sukhuna and Al-Galala Al-Bahariya Plateau. This region is adjacent to the Gulf of Suez rift, which is an active geothermal area, as indicated by the geothermal surface manifestations, such as thermal hot springs. It is a zone between two tectonic plates, which is expected to have several geothermal reservoirs; consequently, it represents a potential area for geothermal prospecting. Aeromagnetic data interpretation was performed to define the deep and shallow structures in the study area and their distribution to select a suitable site and perform more detailed prospection. Consequently, two sites were chosen to conduct a detailed study, with land magnetic and (1D MT) to discover variations in conductivity (resistivity) and fix the depth of predicted geothermal reservoir as well as the distribution of deep and shallow faults which can facilitate geothermal solutions flow and injection to exploit the geothermal source energy. The obtained results showed that the study area is intensely faulted with major NW-SE trend and minor E-W trend. Meanwhile, the (MT) results show several conductive and resistive zones at different depths, which could be correlated with faulting zones, suitable to predict geothermal sources and aquifers.

Magmatic fluid pathways in the upper crust: insights from dense magnetotelluric observations around the Kuju Volcanoes, Japan

SUMMARYMagnetotelluric (MT) observations have revealed subvertical electrical conductors that extend from shallow depths into the mid-crust at various geothermal zones, active volcanoes and active faults worldwide. These deeply rooted subvertical conductors have typically been interpreted to represent entire zones of dedicated fluid transport through the crust. We estimate the high-resolution 3-D crustal resistivity structure below the Kuju Volcanoes, Japan, using dense observations from 153 broad-band MT measurement sites and 40 telluric measurement sites. The resistivity structure highlights subvertical conductors that merge into a deep conductor to the north of the volcanoes, with deep low-frequency earthquakes occurring near the southeastern edge of this subvertical conductor at 10–30 km depth. This deep conductor branches into several subvertical conductors at 2–10 km depth, coinciding with a shallow zone where tectonic earthquakes rarely occur. The surface expressions of active geothermal areas and past volcanic eruptions are all located above the edges of the conductors at 2–6 km depth. Widespread conductive layers exist around the volcanoes above 2 km depth, and their distribution approximately corresponds to a low-gravity-anomaly zone. We discuss the nature of these subvertical conductors, the potential causes of their complex structure and their relationship to local magmatic fluid transport. These subvertical conductors, a shallow clay-rich layer, developed fracture systems and high-strength solidified magma may all contribute to magmatic fluid transport to the surface at the Kuju Volcanoes. In this study, we add the possibility that the edges of these subvertical conductors act as important magmatic fluid pathways.

Potential geothermal structure inferred from the electrical resistivity and seismic reflection models in the western Ilan Plain, NE Taiwan

The Ilan Plain is identified as the western extension of the Okinawa Trough in the northeastern Taiwan subduction system and is considered one of the most active geothermal areas in Taiwan. An east-west extending magma-like body caused by the westward of the Okinawa Trough had been revealed from seismic and geomagnetic studies. Two geological models have been suggested as an extensional strike-slip fault and normal fault models for the deep geothermal field in NE Taiwan. The difference of the main fault in the two geology models is the active normal strike-slip fault or inactive thrust fault and its dip directions. We investigated the electrical resistivity structure beneath the Ilan Plain using audio-magnetotelluric data to delineate the location of its geothermal reservoirs. The 3D electrical resistivity model is highly correlated with the normal fault model. The electrical resistivity model shows that the high conductivity anomaly distributes in the depths of 500-1,100 m south of the drilled geothermal observation wells. We correlate the anomalous high conductor with the reservoir and it could be controlled by the Chuoshui Fault and the Chukeng Fault. The meteoric water may propagate down through the high-permeability fault system that creates the geothermal system.

Structural control on hydrothermal upwelling in the Ixtlán de los Hervores geothermal area, Mexico

Hot springs and related deposits are common features in active geothermal areas around the world. In this study, centered on the Ixtlán de los Hervores geothermal zone (Michoacán, Mexico), we analyzed the distribution of active hydrothermal manifestations and hot-spring deposits as well as the local stratigraphy to determine the influence of the faults in the hydrothermal fluid circulation. The hydrothermal manifestations are mainly represented by hot springs with water temperatures up to 92 °C (depositing silica sinter at the surface). All the hydrothermal features are located within a tectonic depression controlled by the potentially active Ixtlán-Encinal fault. Inside this depression, lacustrine sediments were deposited from Pliocene up to the Hispanic colony period (~XVI–XIX centuries). A pre-Hispanic silica-sinter layer was identified beneath the lacustrine sediments, as well as a debris flow deposit, rich in pottery, suggesting that the debris flow may have affected local inhabitants during pre-Hispanic times.

Tree ferns and tea trees in biogeochemical exploration for epithermal Au and Ag in New Zealand

Biogeochemical orientation surveys were undertaken at low sulphidation epithermal Au–Ag occurrences in the Hauraki Goldfield–Coromandel Volcanic Zone and the Taupo Volcanic Zone, and at the Waiotapu active geothermal area in the Taupo Volcanic Zone. Several plant species were sampled, including the foliage of tree ferns and tea trees. The ferns – silver fern ( ponga ), rough tree fern ( wheki ) and black tree fern ( mamaku ) – were ubiquitous and were the easiest species to sample, although tea tree was the dominant genus at Waiotapu. At the Waiotapu geothermal area, significantly higher concentrations of Ag, Au, Sb, As, Cs and Rb were present in samples close to Champagne Pool than elsewhere, confirming its location as the main outflow source of Au, Ag and their pathfinder elements. The fern survey areas at Luck at Last mine, Pine Sinter and Ohui in the Coromandel Volcanic Zone each exhibited biogeochemical anomalies, which successfully highlighted most of the known quartz veins and provided additional anomalies for further investigation. Rough tree fern was the most common species at Goldmine Hill, Puhipuhi (Taupo Volcanic Zone). Although this species absorbs lower concentrations of many elements than the silver fern, the spatial distribution of elements is of greater significance than their absolute concentrations. The highest Au, Ag, As and Al concentrations occurred in samples from a ridge extending WNW from Goldmine Hill. Sb and Bi were at anomalous levels in an area peripheral to the precious metal anomalies, indicating the potential zonation of elements distal from the Au and Ag deposits. Supplementary material: The full datasets on the fern and tea tree chemistry, including quality assurance/quality control and multi-element plots, are available free of charge through the GNS Science website (search for Dunn) at http://shop.gns.cri.nz/publications/science-reports/ .

Application and reliability of calcic amphibole thermobarometry as inferred from calc-alkaline products of active geothermal areas in the Andes

Igneous thermobarometry may contribute to locate the upper-crust heat source/s representing one of the main factors required to establish the potential of high enthalpy geothermal areas through models of the heat flux. To test this possibility, we applied amphibole thermobarometry to some of the youngest lavas and pyroclastics (andesite to rhyolite) of Apacheta and La Torta (Chile) and Chachimbiro (Ecuador) areas representing medium to high enthalpy geothermal systems located in two different crustal contexts along the Andean active continental margins of South America. We used the robust application of Ridolfi and Renzulli (2012) allowing to estimate the intrinsic physico-chemical parameters with reasonably low uncertainties (T ± 24 °C, P ± 12%, fO2 ± 0.4 log units) and the composition of the melt in equilibrium with Mg-rich calcic amphibole in a wide range of conditions, up to 1130 °C and 2.2 GPa. In addition, analyses of the intra-crystalline compositional and textural variations allowed us to propose a method to distinguish between chemically homogeneous and heterogeneous amphiboles, avoiding some incorrect applications of the Ridolfi and Renzulli (2012)'s equations and thus unreliable results.Thermobarometric constraints indicate a polybaric crystallization of magmas below the Chilean geothermal areas of Apacheta and La Torta. In the last 150 ka, the feeding systems of these areas mainly consisted of shallow silicic magma chambers at depths of 4–8 km (740–840 °C), giving rise to dacite domes (tortas). Amphiboles in the rhyolite lava flows, erupted earlier (Pliocene-Pleistocene) during the activity of the nearby Apacheta-Aguilucho Volcanic Complex, show a similar T-depth range (780–810 °C, 4–6 km). At deeper levels (10–20 km), the depths estimated using amphiboles from the magmatic enclaves (in the dacite domes) and from the andesite lavas are approximately aligned along the upper morphologic margins of the well geophysically constrained Altiplano-Puna Magma Body (APMB; a partially melted zone in the upper crust where the S-waves velocities are <2.9 km/s), with estimated temperatures of 850–1010 °C. Heat source contributions for the investigated Chilean geothermal areas should therefore be represented by both the shallower magma bodies and the huge APMB.The Holocene products of the Ecuadorian Chachimbiro geothermal area indicate amphibole crystallization from 7 to 17 km depth at temperature conditions in the range of 800–910 °C. The occurrence of two separated regions of magma storage at approximately 230 ± 30 MPa and 380 ± 60 MPa is discussed. They should be taken into account as heat sources for this Ecuadorian geothermal area.

Rock geochemistry related to mineralization processes in geothermal areas

Abundant geothermal systems in Indonesia suggest high heat and mass transfer associated with recent or paleovolcanic arcs. In the active geothermal system, the upflow of mixed fluid between late stage hydrothermal and meteoric water might contain mass of minerals associated with epithermal mineralisation process as exemplified at Lihir gold mine in Papua New Guinea. In Indonesia, there is a lack of study related to the precious metals occurrence within active geothermal area. Therefore, in this paper, we investigate the possibility of mineralization process in active geothermal area of Guci, Central Java by using geochemical analysis. There are a lot of conducted geochemical analysis of water, soil and gas by mapping the temperature, pH, Hg and CO2 distribution, and estimating subsurface temperature based on geothermometry approach. Then we also apply rock geochemistry to find minerals that indicate the presence of mineralization. The result from selected geothermal area shows the presence of pyrite and chalcopyrite minerals on the laharic breccias at Kali Putih, Sudikampir. Mineralization is formed within host rock and the veins are associated with gold polymetallic mineralization.

NATURAL DEGASSING OF CARBON DIOXIDE AND HYDROGEN SULPHIDE AND ITS ENVIRONMENTAL IMPACT AT MILOS ISLAND, GREECE

The Aegean region represents an active convergent zone, where continental micro-plates exhibit a complex interaction between the African and the Eurasian plates. The calc-alkaline volcanic activity of the Southern Aegean region developed in various volcanic centers from Soussaki to Nisyros through Methana-Poros, Milos and Santorini. Milos Island has been an active volcano till the middle of Quaternary and is at present characterized by a high enthalpy geothermal system. The volcanism started 3.5 Ma ago and still continues up today in the form of post-volcanic manifestations. Most quiescent volcanoes released large amounts of CO2 and H2S through fumarolic activity and soil diffuse degassing. Numerous small fumaroles occur in various places, mainly at Kalamos and Adamas volcanic areas. Also along the southern coast of the island there are volcanic gas manifestations in the sea. Gases were sampled from fumaroles at Kalamos area as well as from north east part of Adamas village. Furthermore many soil gases were sampled at 50 cm depth and analyzed for their chemical composition. Apart from atmospheric gases (N2 and O2), which sometimes contaminate the samples, the main gas phase is CO2. Sometimes also H2S, CH4 and H2 are present in high amounts while CO and He are always present in trace amounts. The He isotopic composition highlights a significant mantle component. CO2 and H2S concentrations higher than in the normal atmosphere can be stimulating for plant growth until certain levels and detrimental above them. As for many active geothermal areas of the world also H2S and CO2 concentrations measured in the area of Milos could be of concern for human health.

Developing a web-based spatial decision support system for geothermal exploration at the Olkaria geothermal field

ABSTRACTGeothermal exploration is a complex process that spans a number of disciplines. Before a decision is made to drill a geothermal well, there is need for an extensive exploration process to determine the most suitable location. The process of evaluating and analyzing data from individual scientific disciplines can be complex and tedious. Attempts have been made at solving this problem using GIS-based tools but the uptake of these tools is often hindered by the limited knowledge of GIS by decision makers. This paper presents an approach for solving the geothermal exploration question through a web-based spatial decision support system (SDSS) that incorporates the various geosciences through a multi-criteria spatial decision analysis model. The results reveal a decision-making gap that is to be filled using a novel, automated exploration SDSS. This approach hypothesizes an easier and faster decision-making process. The research focuses on Olkaria, an active geothermal area in Kenya, East Africa and highlights a pragmatic approach to identifying priority areas for drilling. It evaluates contributions made by many disciplines in identifying potential sites ideal for harnessing geothermal energy and the gaps that emerge in an effort to synergize the results from the different disciplines.

Changes in aerial thermal infrared signature over the Rotorua Geothermal Field, New Zealand: 1990–2014

Remote sensing techniques can be used on large and small scales to aid mapping and monitoring of geothermal surface features. Monitoring changes in geothermal surface features can provide some insight into the changing processes of geothermal fields caused by natural or anthropogenic sources. This study presents a geothermal-field scale survey using aerial thermal infrared (TIR) techniques to monitor changes in the lateral extent of geothermal surface features over time.Data from aerial TIR surveys conducted over the Rotorua Geothermal Field (RGF) (New Zealand) in 1990 and 2014 are compared to identify areas that may have changed between the two surveys. Differences in the area of geothermal surface features with temperatures greater than 28°C and an area greater than 1m2 between 1990 and 2014 have been estimated for six zones of the RGF and used to infer the change over the entire RGF.Within error estimates, the Ngapuna, Ohinemutu, Kuirau, Arikikapakapa zones are calculated to have similar geothermal surface areas, while Sulphur Flats and Whakarewarewa zones show a decrease in the area of geothermal activity between 1990 and 2014. Spatial patterns in changes between 1990 and 2014 are examined to determine potential near-surface geothermal processes.

Genetic divergence and isolation by thermal environment in geothermal populations of an aquatic invertebrate.

Temperature is one of the most influential forces of natural selection impacting all biological levels. In the face of increasing global temperatures, studies over small geographic scales allowing investigations on the effects of gene flow are of great value for understanding thermal adaptation. Here, we investigated genetic population structure in the freshwater gastropod Radix balthica originating from contrasting thermal habitats in three areas of geothermal activity in Iceland. Snails from 32 sites were genotyped at 208 AFLP loci. Five AFLPs were identified as putatively under divergent selection in Lake Mývatn, a geothermal lake with an almost 20°C difference in mean temperature across a distance of a few kilometres. In four of these loci, variation across all study populations was correlated with temperature. We found significant population structure in neutral markers both within and between the areas. Cluster analysis using neutral markers classified the sites mainly by geography, whereas analyses using markers under selection differentiated the sites based on temperature. Isolation by distance was stronger in the neutral than in the outlier loci. Pairwise differences based on outlier FST were significantly correlated with temperature at different spatial scales, even after correcting for geographic distance or neutral pairwise FST differences. In general, genetic variation decreased with increasing environmental temperature, possibly suggesting that natural selection had reduced the genetic diversity in the warm origin sites. Our results emphasize the influence of environmental temperature on the genetic structure of populations and suggest local thermal adaptation in these geothermal habitats.

Long-period seismic events with strikingly regular temporal patterns on Katla volcano's south flank (Iceland)

Katla is a threatening volcano in Iceland, partly covered by the Mýrdalsjökull ice cap. The volcano has a large caldera with several active geothermal areas. A peculiar cluster of long-period seismic events started on Katla's south flank in July 2011, during an unrest episode in the caldera that culminated in a glacier outburst. The seismic events were tightly clustered at shallow depth in the Gvendarfell area, 4km south of the caldera, under a small glacier stream at the southern margin of Mýrdalsjökull. No seismic events were known to have occurred in this area before. The most striking feature of this seismic cluster is its temporal pattern, characterized by regular intervals between repeating seismic events, modulated by a seasonal variation. Remarkable is also the stability of both the time and waveform features over a long time period, around 3.5years. We have not found any comparable examples in the literature. Both volcanic and glacial processes can produce similar waveforms and therefore have to be considered as potential seismic sources. Discerning between these two causes is critical for monitoring glacier-clad volcanoes and has been controversial at Katla. For this new seismic cluster on the south flank, we regard volcano-related processes as more likely than glacial ones for the following reasons: 1) the seismic activity started during an unrest episode involving sudden melting of the glacier and a jökulhlaup; 2) the glacier stream is small and stagnant; 3) the seismicity remains regular and stable for years; 4) there is no apparent correlation with short-term weather changes, such as rainstorms. We suggest that a small, shallow hydrothermal system was activated on Katla's south flank in 2011, either by a minor magmatic injection or by changes of permeability in a local crack system.

Multidisciplinary constraints of hydrothermal explosions based on the 2013 Gengissig lake events, Kverkfjöll volcano, Iceland

Hydrothermal explosions frequently occur in geothermal areas showing various mechanisms and energies of explosivity. Their deposits, though generally hardly recognised or badly preserved, provide important insights to quantify the dynamics and energy of these poorly understood explosive events. Furthermore the host rock lithology of the geothermal system adds a control on the efficiency in the energy release during an explosion. We present results from a detailed study of recent hydrothermal explosion deposits within an active geothermal area at Kverkfjöll, a central volcano at the northern edge of Vatnajökull. On August 15th 2013, a small jökulhlaup occurred when the Gengissig ice-dammed lake drained at Kverkfjöll. The lake level dropped by approximately 30 m, decreasing pressure on the lake bed and triggering several hydrothermal explosions on the 16th. Here, a multidisciplinary approach combining detailed field work, laboratory studies, and models of the energetics of explosions with information on duration and amplitudes of seismic signals, has been used to analyse the mechanisms and characteristics of these hydrothermal explosions. Field and laboratory studies were also carried out to help constrain the sedimentary sequence involved in the event. The explosions lasted for 40–50 s and involved the surficial part of an unconsolidated and hydrothermally altered glacio-lacustrine deposit composed of pyroclasts, lavas, scoriaceous fragments, and fine-grained welded or loosely consolidated aggregates, interbedded with clay-rich levels. Several small fans of ejecta were formed, reaching a distance of 1 km north of the lake and covering an area of approximately 0.3 km2, with a maximum thickness of 40 cm at the crater walls. The material (volume of approximately 104 m3) has been ejected by the expanding boiling fluid, generated by a pressure failure affecting the surficial geothermal reservoir. The maximum thermal, craterisation and ejection energies, calculated for the explosion areas, are on the order of 1011, 1010 and 109 J, respectively. Comparison of these with those estimated by the volume of the ejecta and the crater sizes, yields good agreement. We estimate that approximately 30% of the available thermal energy was converted into mechanical energy during this event. The residual energy was largely dissipated as heat, while only a small portion was converted into seismic energy. Estimation of the amount of freshly-fragmented clasts in the ejected material obtained from SEM morphological analyses, reveals that a low but significant energy consumption by fragmentation occurred. Decompression experiments were performed in the laboratory mimicking the conditions due to the drainage of the lake. Experimental results confirm that only a minor amount of energy is consumed by the creation of new surfaces in fragmentation, whereas most of the fresh fragments derive from the disaggregation of aggregates. Furthermore, ejection velocities of the particles (40–50 m/s), measured via high-speed videos, are consistent with those estimated from the field. The multidisciplinary approach used here to investigate hydrothermal explosions has proven to be a valuable tool which can provide robust constraints on energy release and partitioning for such small-size yet hazardous, steam-explosion events.

Methane Oxidation and Molecular Characterization of Methanotrophs from a Former Mercury Mine Impoundment.

The Herman Pit, once a mercury mine, is an impoundment located in an active geothermal area. Its acidic waters are permeated by hundreds of gas seeps. One seep was sampled and found to be composed of mostly CO2 with some CH4 present. The δ13CH4 value suggested a complex origin for the methane: i.e., a thermogenic component plus a biological methanogenic portion. The relatively 12C-enriched CO2 suggested a reworking of the ebullitive methane by methanotrophic bacteria. Therefore, we tested bottom sediments for their ability to consume methane by conducting aerobic incubations of slurried materials. Methane was removed from the headspace of live slurries, and subsequent additions of methane resulted in faster removal rates. This activity could be transferred to an artificial, acidic medium, indicating the presence of acidophilic or acid-tolerant methanotrophs, the latter reinforced by the observation of maximum activity at pH = 4.5 with incubated slurries. A successful extraction of sterol and hopanoid lipids characteristic of methanotrophs was achieved, and their abundances greatly increased with increased sediment methane consumption. DNA extracted from methane-oxidizing enrichment cultures was amplified and sequenced for pmoA genes that aligned with methanotrophic members of the Gammaproteobacteria. An enrichment culture was established that grew in an acidic (pH 4.5) medium via methane oxidation.

Structural controls on fluid pathways in an active rift system: A case study of the Aluto volcanic complex

In volcanically and seismically active rift systems, preexisting faults may control the rise and eruption of magma, and direct the flow of hydrothermal fluids and gas in the subsurface. Using high-resolution airborne imagery, field observations, and CO 2 degassing data on Aluto, a typical young silicic volcano in the Main Ethiopian Rift, we explore how preexisting tectonic and volcanic structures control fluid pathways and spatial patterns of volcanism, hydrothermal alteration and degassing. A new light detection and ranging (lidar) digital elevation model and evidence from deep geothermal wells show that the Aluto volcanic complex is dissected by rift-related extensional faults with throws of 50–100 m. Mapping of volcanic vent distributions reveals a structural control by either rift-aligned faults or an elliptical caldera ring fracture. Soil-gas CO 2 degassing surveys show elevated fluxes (>>100 g m –2 d –1 ) along major faults and volcanic structures, but significant variations in CO 2 flux along the fault zones reflect differences in near-surface permeability caused by changes in topography and surface lithology. The CO 2 emission from an active geothermal area adjacent to the major fault scarp of Aluto amounted to ∼60 t d –1 ; we estimate the total CO 2 emission from Aluto to be 250–500 t d –1 . Preexisting volcanic and tectonic structures have played a key role in the development of the Aluto volcanic complex and continue to facilitate the expulsion of gases and geothermal fluids. This case study emphasizes the importance of structural mapping on active rift volcanoes to understand the geothermal field as well as potential volcanic hazards.

Crustal structure in and around the Onikobe geothermal area, northeastern Honshu, Japan, inferred from the spatial variation of coda decay

The Onikobe area is an active geothermal area situated in the Ou backbone range of northeastern Honshu, Japan. It is home to calderas from the Tertiary to Quaternary eras and active volcanoes. A systematic spatial variation of Qc has been found in this area: Qc values are lower at stations in and around calderas than at other stations. The amplitude of coda waves with high Qcs decreases more slowly after a lapse time of around 7–10s than that with low Qcs. In the present study, to determine causes for these coda decay variations, coda envelopes were synthesized in a structure model in which high attenuation zones existed beneath the Onikobe and Sanzugawa calderas and where scattering coefficients were higher in the lower crust than in the upper crust. Using hypocenters shallower than 10km, envelopes were calculated for 256 station-hypocenter pairs with epicentral distances of less than 10km. It was assumed that the coda waves were composed of S–S scattered waves, and that the scattering was single and isotropic. The observed features of the Qc distribution were reproduced in the synthesis, and synthesized envelopes were found to mostly coincide with observed decay curves. The top of high attenuation zones was thus estimated as being deeper than 7.5km. The structure assumed for the synthesis was consistent with that of previous studies. We consider that the structure model used was appropriate, and that high attenuation zones beneath calderas and the reflective lower crust caused the spatial variation of the Qc and decay curves in the Onikobe area. We also consider that studies using coda decay would be beneficial in detecting high attenuation zones and the reflective lower crust.

Low Angle Normal Fault (LANF)-zone architecture and permeability features in bedded carbonate from inner Northern Apennines (Rapolano Terme, Central Italy)

Fault zones have the capacity to be hydraulic conduits within upper crustal levels, allowing migration of large volume of fluids through shallow and deeper geological environments. Low-angle normal faults (LANFs) crosscutting carbonate rocks produce damaged volumes that may have a relevant role in channelling or hosting geothermal fluids, therefore deserving of investigation to better predict mining targets. Deformation along LANFs zones, dissecting carbonate successions, produces permeable volumes presently exploited in the Larderello and Monte Amiata geothermal areas (Italy). In this paper, the architectural and permeability features of an exhumed LANF-zone exposed in the Northern Apennines, (Rapolano Terme, central Italy), affecting Cretaceous bedded limestone, are presented. Such a fault was not affected by circulation of geothermal fluids, but its features could reveal much on the potential impact on fluids migration in the active geothermal areas, therefore resulting an intriguing analogue. The study LANF-zone consists of faults, which enucleated at depth >4km. During its earlier stage of evolution, dissolution seams, often arranged in s–c fabric, characterised the whole damage zone. Dissolution seams developed under very low-grade metamorphism (T=100–150°C) as indicated by illite crystallinty analyses. Fault zone architecture and permeability features changed during the fault growth and exhumation. Permeability heterogeneity and anisotropy characterised the LANF zone during its development. If geofluids circulated within the fault zone, it could be an effective barrier during its earlier evolution, being accompanied by dissolution seams. On the contrary, it could play as combined barriers–conduits during its later evolution (progressively at shallower levels) being characterised by intersecting fault planes, which define pipe-like conduits parallel to the direction of the tectonic transport. Such a configuration could have the capacity to impact on fluids migration for long paths across the upper crustal levels. This adds significant information for predicting deeper geothermal circuits and the location of potential exploitable reservoirs in active tectonic environments.

Hydrogeochemical and seismological exploration for geothermal resources in South Sinai, Egypt utilizing GIS and remote sensing

Geographic information system and remote sensing techniques are used to determine the spatial association between the hydrogeochemical and seismological evidences of well-known geothermal fields in South Sinai. Manipulation, combination, overlay, integration and reattribution GIS functions have been used to explore the possible new occurrences of geothermal resources in South Sinai. Moreover, surface observations and lineament analysis of satellite images are used to delineate the active geothermal areas. The distribution of recent earthquake epicentres over South Sinai shows three main active trends (N 6° E, N 40°–75° E and N 50°–60° W) conformable with the long fault extensions extracted from ETM+7 and ASTER GDEM satellite images and comprise the well-known hot springs in South Sinai. It is found that wherever the N 6° E trend intersects both of N 50°–60° W or N 40°–75° E, the temperature of spring waters is remarkably increased. This feature could be attributed to the deep penetration of groundwater along the N 6° E fault trend (Gulf of Aqaba trend). The seismicity patterns of well-known and newly predicted geothermal sites show that the majority of earthquakes have focal depth range between 3 and 33 km (within the upper Earth crust) and have micro to moderate magnitude (0.5 ≥ Mb ≤ 4.5). In addition, the maximum focal depth of events reached up to 50 km at the Hammam Faroun area revealing the deep-seated thermal source. The main chemical type of the known thermal water of South Sinai is Cl-Na, indicating a long flow pathway of this water. The high calcium contents of thermal water of South Sinai are accompanied with remarkably low sulphates. This could be attributed to the microbial or thermal reduction of sulphates in contact with organic carbon which is confirmed by the emission of H2S gas observed at the known thermal field sites. As a result, thermal waters of the Hammam Faroun and Hammam Musa are undersaturated with respect to gypsum and anhydrite. The hydrochemistry of the newly predicted thermal sites exhibit similar pattern of the known thermal waters. Such observations are used as indicators to locate six predicted new occurrences of geothermal fields in South Sinai.

Geothermal activity helps life survive glacial cycles

Climate change has played a critical role in the evolution and structure of Earth's biodiversity. Geothermal activity, which can maintain ice-free terrain in glaciated regions, provides a tantalizing solution to the question of how diverse life can survive glaciations. No comprehensive assessment of this "geothermal glacial refugia" hypothesis has yet been undertaken, but Antarctica provides a unique setting for doing so. The continent has experienced repeated glaciations that most models indicate blanketed the continent in ice, yet many Antarctic species appear to have evolved in almost total isolation for millions of years, and hence must have persisted in situ throughout. How could terrestrial species have survived extreme glaciation events on the continent? Under a hypothesis of geothermal glacial refugia and subsequent recolonization of nongeothermal regions, we would expect to find greater contemporary diversity close to geothermal sites than in nongeothermal regions, and significant nestedness by distance of this diversity. We used spatial modeling approaches and the most comprehensive, validated terrestrial biodiversity dataset yet created for Antarctica to assess spatial patterns of diversity on the continent. Models clearly support our hypothesis, indicating that geothermally active regions have played a key role in structuring biodiversity patterns in Antarctica. These results provide critical insights into the evolutionary importance of geothermal refugia and the history of Antarctic species.