South Flank Research Articles

Seismic Evidence for a Shallow Detachment Beneath Kīlauea's South Flank During the 2018 Activity

AbstractWe investigate earthquake distribution and focal mechanisms associated with the 2018 Kīlauea volcano eruption in Hawaii. Our high‐precision earthquake relocations delineate an aseismic zone bounded by two subhorizontal bands of seismicity at 3.5 and 7 km depths beneath the eastern south flank, both of which are dominated by the shallow‐dipping reverse faulting during the 2018 activity. We interpret the deeper seismicity as related to the basal décollement that separates the volcanic edifice from the oceanic crust. The shallower seismicity is a feature exhibited in the recent activity and, which we propose, reveals a detachment that either represents the contact between Mauna Loa and Kīlauea volcanoes or coincides with the onland extension of the base of the Hilina slump. We suggest that large earthquakes, such as the 1975 Mw 7.7 and the 2018 Mw 6.9 mainshocks, are capable of triggering failures of both the basal décollement and the shallower surface.

Geochemistry of Basaltic Merbabu Volcanic Rocks, Central Java, Indonesia

DOI: 10.17014/ijog.7.2.161-178The studied area is located along the hiking track of Kajor - Selo, the south flank of Merbabu Volcano, Central Java, Indonesia. Olivine basalt and augite-rich basalt compose the volcanic rocks. A geochemical study recognizes these basalts which tend to originate from the product of tholeiitic magma, in terms of transitional enriched mantle source. It is interpreted to have been formed as primary magma that mixed later with higher degrees of partial melting with a mantle wedge. Both fl uid and melt were derived from the mixing of lower active continental margin and subducting oceanic slab. This study also shows general trends of increasing incompatible elements, i.e. Rb, Ba, Pb2+, and Sr as LIL trace elements and Th, U, Nb, Ce, Zr, Hf, Nb, and Ta as HFS element comparing to basaltic andesites exposed at Thekelan, they show decreasing compatible of MgO, Fe2O3*, Al2O3, CaO, TiO2, Ni, Sr, and Ba in line with increasing SiO2. It was fractional crystallization process, shown by the slightly wide variation of Rb/Zr and La/Sm that indicates random crustal contamination.

Seismic velocity variations associated with the 2018 lower East Rift Zone eruption of K\u012blauea, Hawai\u02bbi

The 2018 lower East Rift Zone eruption of Kīlauea (Hawai‘i) marked a dramatic change in the volcano’s 35-year-long rift zone eruption. The collapse of the middle East Rift Zone vent Pu‘u ‘Ō‘ō was followed by one of the volcano’s most voluminous eruptions in 500 years. Over the course of this 3-month eruption, the draining of summit-stored magma led to near-daily collapses of a portion of the caldera and ultimately up to 500 m of summit subsidence. While deformation data indicated that the summit and middle East Rift Zone were inflating for the previous several years, why Pu‘u ‘Ō‘ō collapsed and what initiated down-rift dike propagation remains unclear. Using ambient noise seismic interferometry, we show that a Ml5.3 decollement earthquake beneath Kīlauea’s south flank in June 2017 induced a coseismic decrease of up to 0.30% in seismic velocity throughout the volcano. This velocity decrease may have been caused by dynamic stress–induced shallow crustal fracture, i.e., weakening to dilatant crack growth, and was greatest near Pu‘u ‘Ō‘ō. Additionally, we verify a pre-eruptive increase in seismic velocity, consistent with increasing pressurization in the volcano’s shallow summit magma reservoir. This velocity increase occurred coincident with the first in a series of lower-crustal earthquake swarms, 6 days before a 2-month period of rapid summit and middle East Rift Zone inflation. The increase in up-rift magma-static pressure, combined with the pre-existing weakness from the June 2017 earthquake, may have facilitated down-rift dike propagation and the devastating 2018 eruption.

From Sensor to Cloud: An IoT Network of Radon Outdoor Probes to Monitor Active Volcanoes.

While radon in soil gases has been identified for decades as a potential precursor of volcanic eruptions, there has been a recent interest for monitoring radon in air on active volcanoes. We present here the first network of outdoor air radon sensors that was installed successfully on Mt. Etna volcano, Sicily, Italy in September 2019. Small radon sensors designed for workers and home dosimetry were tropicalized in order to be operated continuously in harsh volcanic conditions with an autonomy of several months. Two stations have been installed on the south flank of the volcano at ~3000 m of elevation. A private network has been deployed in order to transfer the measurements from the stations directly to a server located in France, using a low-power wide-area transmission technology from Internet of Things (IoT) called LoRaWAN. Data finally feed a data lake, allowing flexibility in data management and sharing. A first analysis of the radon datasets confirms previous observations, while adding temporal information never accessed before. The observed performances confirm IoT solutions are very adapted to active volcano monitoring in terms of range, autonomy, and data loss.

A New Fluid-Flow Model for the Genesis of Banded Iron Formation-Hosted Martite-Goethite Mineralization, with Special Reference to the North and South Flank Deposits of the Hamersley Province, Western Australia

AbstractThe North and South Flank deposits are located on the flanks of the Weeli Wolli anticline at Mining Area C in the central Hamersley Province. Supergene martite-goethite mineralization is hosted within the Marra Mamba Iron Formation and is developed over a strike length of more than 60 km. This multibillion metric ton resource has been drilled out on a 150- × 50- to 50- × 50-m grid, thus providing us with an unprecedented data set for analysis. This study synthesizes the drill hole data and presents a physical process model that can account for the observed distribution of mineralization.A fluid and mass flux model is proposed which envisages a three-stage process: (1) leaching of Fe from banded iron formation (BIF) in the vadose zone by reduced, acidic, meteoric-derived fluids; (2) penetration of an Fe-rich supergene-fluid plume, driven by gravity and focused by bedding-parallel permeability into the body of ambient alkaline groundwater, effecting nonredox, mimetic replacement of magnetite by hematite and of the gangue minerals (carbonate, silicate, and chert) by goethite coupled with the release of silica into the fluid phase; and (3) a change from silica leaching to silica deposition on the downdip margins of the system before the ore-fluid plume is eventually diluted and becomes indistinguishable from the surrounding body of groundwater.Despite the undoubted secondary role played by structurally enhanced permeability, the primary control on ore-fluid hydrology is gravity-driven flow along bedding planes. This central observation explains every observed feature of the three-dimensional distribution of martite-goethite mineralization, and the inherited structural architecture simply provides the context for this process to play out. This type of control is by no means obvious–the ingress of meteoric fluids during later lateritic weathering of the mineralization does not show this control and produces broadly subhorizontal, bedding-discordant zones of overprinting.The fundamental control exerted on the distribution of martite-goethite mineralization by bedding-plane permeability within BIF horizons suggests that the supergene ore-fluid plume created its own porosity via the relevant ore-forming reactions, and that these were in turn controlled by bedding. A corollary of the pseudomorphic replacement process, both the generation of hematite after magnetite and goethite after gangue phases, is that it typically introduces porosity. The mineralizing process thus creates porosity (and potentially permeability) and is likely to be self-propagating as long as there is continuous supply of ore fluid. This putative active porosity-generation process may be an important clue as to the unique conditions of martite-goethite ore formation. Indeed, it may be that the distribution of magnetite is the critical controlling feature of these ore systems, as the nonredox transformation to hematite not only releases Fe2+ to the fluid phase but concurrently introduces porosity. Further research is required to formulate a comprehensive chemical (as opposed to physical) process model for supergene martite-goethite ore formation.Based on the physical process model presented here, the development of a large-scale martite-goethite mineralizing system requires continued delivery of unleached BIF (and, perhaps ultimately, previously mineralized martite-goethite ore) into the vadose zone. The Hamersley Province has been undergoing significant uplift since at least 60 Ma. Preliminary dating of martite-goethite ores from Mining Area C indicates that they formed at about 45 Ma, at a time when the local climate was temperate and wetter than today. The combination of ongoing uplift and a wet, temperate climate is likely to be the key to the widespread formation of martite-goethite deposits in the Hamersley Province.

Triggering relationships between magmatic and faulting processes in the May 2018 eruptive sequence at Kīlauea volcano, Hawaii

SUMMARYThe May 2018 activity at Kīlauea Volcano, Hawaii involved magma transport and dyke intrusion along the East Rift Zone (ERZ) and nucleation of the 4 May 2018 M 6.9 earthquake along the basal décollement of Kīlauea's mobile south flank. Combined Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) measurements captured the deformation sequence associated with the dyke intrusion, main shock and eruption episode along the ERZ. The earthquake was encouraged by static stress changes from the preceding magma reservoir inflation, ERZ expansion and fault creep on the décollement downdip of the rupture. Slip models derived from the inversion of GPS displacements indicate peak coseismic slip of 2–3 m. Our model analyses, including of the pre-May 2018 deformation, suggest that prior to this event there was no slip on the section of the décollement that ruptured in the earthquake. The observed magma inflation, rapid fault creep on the décollement and coseismic rupture reflect complex cyclic interactions between the magmatic and faulting processes.

A Breccia Pipe in the Deseret Limestone, South Flank of the Uinta Mountains, Northern Utah

A breccia pipe is a cylindrical- or irregular-shaped mass of brecciated rock. A breccia consists of broken, angular fragments of rock cemented together by a fine-grained matrix. Hydrothermal breccia pipes form when hydrothermal solutions force their way towards the surface through zones of weakness or fracture zones and naturally break up the rocks in the process, i.e., hydrofracturing; breccia pipes can also form by collapse. Hydrothermal breccia pipes can contain ore deposits and, as will be discussed later, are associated with some large oil and gas accumulations in southeastern Utah.

Sediment sources and transport by the Kahiltna Glacier and other catchments along the south side of the Alaska Range, Alaska

AbstractErosion related to glacial activity produces enormous amounts of sediment. However, sediment mobilization in glacial systems is extremely complex. Sediment is derived from headwalls, slopes along the margins of glaciers, and basal erosion; however, the rates and relative contributions of each are unknown. To test and quantify conceptual models for sediment generation and transport in a simple valley glacier system, we collected samples for 10Be analysis from the Kahiltna Glacier, which flows off Denali, the tallest mountain in North America. We collected angular quartz clasts on bedrock ledges from a high mountainside above the equilibrium line altitude (ELA), amalgamated clast samples from medial moraines, and sand samples from the river below the glacier. We also collected sand from nine other rivers along the south flank of the Alaska Range. In the upper catchment of the Kahiltna drainage system, toppling, rockfall, and slab collapse are significant erosional processes. Erosion rates of hundreds of millimeters per thousand years were calculated from 10Be concentrations. The 10Be concentrations in amalgamated samples from medial moraines showed concentrations much lower than those measured from the high mountainside, a result of the incorporation of thick, and effectively unexposed, blocks into the moraine, as well as the incorporation of material from lower-elevation nearby slopes above the moraines. The 10Be sediment samples from downstream of the Kahiltna Glacier terminus showed decreasing concentrations with increasing distance from the moraine, indicating the incorporation of material that was less exposed to cosmic rays, most likely from the glacier base as well as from slopes downstream of the glacier. Taken together, 10Be concentrations in various samples from the Kahiltna drainage system indicated erosion rates of hundreds of millimeters per thousand years, which is typical of tectonically active terrains. We also measured 10Be concentrations from river sediment samples collected from across the south flank of the Alaska Range. Calculation of basinwide weighted erosion rates that incorporated hypsometric curves produced unrealistically high erosion rates, which indicates that the major source of sediment was not exposed to cosmic rays and was primarily derived from the base of glaciers. Moreover, the apparently high erosion rates suggest that parts of each drainage system are not in erosional steady state with respect to cosmogenic isotope accumulation.

Provenance and sedimentary evolution from the Middle Permian to Early Triassic around the Bogda Mountain, NW China: A tectonic inversion responding to the consolidation of Pangea

Abstract The tectonic attribute and evolution of the Bogda Mountain are crucial to understand the Palaeozoic development of the Tian Shan and Central Asian Orogenic Belt (CAOB). In this work, we combined sedimentological and geophysical methods such as field section measurements, core analyses, well logs and seismic sections interpretation to study the sedimentary evolution from the Middle Permian to Early Triassic. In addition, provenance analysis was performed for the sediments from both flanks of the Bogda Mountain. This set of data allows to improve the constraint on the tectonic attribute and evolution in this area. The facies studies indicate abrupt changes in depositional environments from the lacustrine-alluvial fan to fan delta during the Middle to Late Permian. The subsidence centers shifted from the Paleo-Bogda Mountain to present Bogda piedmonts. Based on detrital zircon U-Pb geochronology, the North Tian Shan (NTS) Early-Middle Permian post-collisional plutons are identified as the main provenances of the Middle Permian deposits from both flanks. The Upper Permian sample shows a strongly concentrated unimodal age peak of ~305–320 Ma, indicating a single source from the NTS and Bogda Mountain. The Lower Triassic samples in the Chaiwopu Depression (CWD) in the south flank of the Bogda Mountain show obvious sources from the Central Tian Shan (CTS) but these are absent in all samples from the north flank of Bogda Mountain. Meanwhile, the Early Permian ages of ~280–295 Ma which correspond to the bimodal volcanism in the Bogda Mountain occur in both flanks of this mountain. According to the comprehensive geological evidence, the deposition of the Lower Permian–Middle Permian strata probably occurred in a rift extension and expansion setting. A tectonic inversion happened at the beginning of the Late Permian, which resulted in initial uplift of the Bogda Mountain. The uplift also occurred in the NTS and CTS in the Late Permian. This tectonic inversion happened for the whole Junggar Basin and was an important intracontinental tectonic movement, which might result from the consolidation of the Pangea supercontinent.

When the Mountain Went Dark: Trouble at Timberline Lodge in the Early 1950s

Timberline Lodge, located on the south flank of Mount Hood, features stunning views of Mount Jefferson and the Cascade Mountains to the south, is one of Oregon's most popular tourist attractions. Completed in 1938, the lodge was the state's largest recreation project initiated by the Works Progress Administration (WPA). In this research article, Joshua B. Fisher discusses how from its opening to the mid 1950s, “Timberline Lodge transitioned from a panacea for the burgeoning Oregon tourism and ski industry to a mismanaged and deteriorating white elephant,” which resulted from a series of private investors with dubious intentions. Timberline Lodge's history, Fisher describes, “sheds light on the interplay between public and private interests in controlling a key government property,” but calls attention to omissions in public records necessary to answer additional questions and draw further conclusions.

Local provenance of raw materials for prehistoric pottery production at the Spasovine tin placer site (Western Serbia)

Archaeological finds at Spasovine, on the south flank of Mt Cer, near the town of Milina, indicate that it was settled in the Eneolithic and seasonally inhabited for tin placer mining in the Late Bronze Age. The site is highly disturbed and abraded domestic pottery is the most common material found. An analysis of the mineralogical assemblages that comprise the temper sand in a subset of the prehistoric pottery sherds from the site indicate that the sand was obtained from the adjacent Milinska River. Key minerals that link the pottery to on-site production from local materials include almandine-spessartine series garnets, the tin-bearing mineral cassiterite (SnO2) and a microlite group mineral ([Ca,Sn,U]2[Ta,Nb]2O6(OH,F]). The unusually common occurrence of cassiterite within the pottery sherds relative to the abundance in the Milinska today suggests that the tin ore grade in the Milinska River may have been significantly higher in prehistory.

NATO’s Challenges in the South Flank

L’OTAN doit trouver des moyens de relever les défis en matière de sécurité. De nouvelles menaces émergent de toutes parts : des acteurs étatiques et non étatiques aux terroristes, en passant par les cyberattaques et les attaques hybrides. Par conséquent, l’Alliance doit se préparer sur les plans conceptuel, politique et militaire afin de contribuer à la sécurité de ses États membres en stabilisant davantage son voisinage sud.

The 2011 unrest at Katla volcano: seismicity and geology context

Katla is one of the most active volcanoes in Iceland and is characterised by persistent seismicity. It is partly covered by the Mýrdalsjökull glacier and its historic activity is dominated by phreatomagmatic eruptions within the caldera associated with catastrophic glacial floods. In July 2011 a sudden jökulhlaup was released from the glacier, associated with tremor, elevated seismicity inside the caldera and a new cluster of seismicity on the south flank. This was likely caused by a hydrothermal or magmatic event, possibly a small subglacial eruption. Similar unrests occurred in 1955 and 1999. We have identified changes of the seismicity pattern coinciding with the 2011 unrest, suggesting a modification in the volcanic system. It may be speculated that if the persistent seismicity at Katla is an indication of a pressurized magma system ready to erupt, small events like those of 1955, 1999 and 2011 may trigger larger eruptions in the future. We have also conducted a pilot study of the geology of the southern flank, where the new seismicity is recorded, and identified sources for flank eruptions in the recent eruptive history of Katla. These include rhyolitic domes and surtseyan craters. Therefore, a wide range of volcanic processes have to be taken into account as possible source for the new seismicity and volcanic hazard.

The 2017 Eruption of Erta 'Ale Volcano, Ethiopia: Insights Into the Shallow Axial Plumbing System of an Incipient Mid‐Ocean Ridge

AbstractThe final stage of continental breakup is often accompanied by abundant magmatism. Erta 'Ale volcano lies on the Nubia‐Arabia extensional boundary in Afar, Ethiopia, an incipient mid‐ocean ridge. A fissure on the south flank of Erta 'Ale began erupting on 21 January 2017 and has remained active until at least July 2019. We use Sentinel‐1 synthetic aperture radar acquisitions to create a time series of ground displacement measurements at Erta 'Ale from October 2014 to June 2019, covering the eruption and its buildup. In the preeruption period, we observe gradual extension centered on the lava lake, consistent with the opening of an axis‐aligned dike. Using synthetic aperture radar intensity shadows, we show that the long‐lived Erta 'Ale lava lake was stable in this period, indicative of a steady pressure state in the shallow plumbing system. During the initial eruption, we observe surface displacements consistent with a shallow dike intrusion below the eruption site and conduit contraction below the lava lake. The pressure change associated with the cointrusive drop in the lava lake level is sufficient to reproduce the deformation pattern suggesting that the lava lake is well connected to the shallow plumbing system. Subsidence and contraction during the long‐lived eruption indicates the presence of an off‐rift vertically extensive source. We suggest that this may represent a system of stacked sources throughout the upper crust, with melt being more distributed. We also propose that high magma flux on the slow‐spreading Erta 'Ale segment may be facilitating the presence of shallow axial magma bodies.

Relationship between the South China Sea summer monsoon withdrawal and September–October rainfall over southern China

This study reveals a significant positive connection between the interannual variation in the South China Sea (SCS) summer monsoon (SCSSM) withdrawal and September–October rainfall over southern China. Specifically, pronounced positive rainfall anomalies can be found around southern China when the withdrawal of the SCSSM is later than normal. The occurrence of the significant SCSSM withdrawal-southern China rainfall relation may be attributed to both the atmospheric internal dynamics and the sea surface temperature (SST) anomalies over the tropical Pacific. In particular, SST warming over the tropical western North Pacific, which resembles the developing phase of a La Nina, could induce a significant anomalous low-level cyclone over the northern SCS via a Rossby wave-type atmospheric response. The southwesterly wind anomalies on the south flank of this anomalous cyclone favor late SCSSM withdrawal and contribute to more rainfall over southern China via the northward transport of water vapor. In addition, the enhanced quasi-biweekly oscillation and synoptic-scale variation (such as tropical cyclones) during late withdrawal years are also conducive to increased rainfall over southern China. Further analyses found notable interdecadal changes and asymmetry in the connection of the SCSSM withdrawal with southern China rainfall. The factors contributing to the nonstationary and asymmetric nature of this monsoon withdrawal-rainfall relationship are also briefly discussed.

The Accommodation of the South Flank's Motion by the Koa‘e Fault System, Kīlauea, Hawai‘i: Insights From the June 2012 Earthquake Sequence

AbstractThe Koa‘e fault system is a prominent and complex structural element of Kīlauea Volcano, Hawai‘i. On 5 June 2012, a sequence of shallow earthquakes occurred in the central part of the Koa‘e fault system. The Interferometric Synthetic Aperture Radar (InSAR) data from multiple satellites spanning the time of the earthquake occurrence indicate a maximum of ~10‐cm surface displacement above the seismic events in the Koa‘e. The Global Positioning System (GPS) data from multiple stations show that there was a slow slip event in the south flank in late May 2012. Field visits to the fault after the earthquakes revealed ground cracks. In this study, we combine the seismic, InSAR, GPS data, and field observations to investigate the characteristics of the Koa‘e fault system. We relocate the seismic events in the central part of the Koa‘e fault system, compute the focal mechanisms for the events in the June 2012 earthquake sequence, invert for a two‐fault model based on the surface deformation, and discuss their relationships with the 2012 slow slip event. Based on our Coulomb stress‐change calculation, we infer that the 2012 slow slip event may have triggered both the seismic events and the surface deformation and played a major role in the evolution of the Koa‘e fault system and the accommodation of the south flank's motion. Our integrated analyses are helpful to constrain the fault geometry in the Koa‘e system and to shed light on the role of Koa‘e in the structural evolution of Kīlauea.

Lower-Tropospheric Influences on the Timing and Intensity of Afternoon Severe Convection over Modest Terrain in a Convection-Allowing Ensemble

AbstractA 50-member convection-allowing ensemble is used to examine effects of daytime PBL evolution and ambient flow interacting with modest terrain features on convection initiation (CI) in the lee of the Rocky Mountains. The examined case (4 June 2015) has isolated supercell storms that initiate during mid- to late afternoon along the northern portion of the Palmer Lake Divide, which is a ~0.5-km-deep zonally oriented terrain feature in east-central Colorado that extends eastward from the Rocky Mountains. To diagnose factors most crucial to storm development, two 10-member subensembles are constructed from the full 50-member ensemble. One subensemble (STRONG) has storm locations with mature storm intensities, and average timing of CI similar to that observed. The other subensemble (WEAK) has fewer storms, with generally weaker intensity, and delayed CI. Environmental composites constructed from these subensembles reveal a stronger surface horizontal convergence zone and moisture gradient in STRONG, resulting from 2–3.5 m s−1 stronger southerly winds on the south flank of the convergence zone. The stronger southerlies result from accelerated PBL growth and momentum mixing in the presence of strong low-to-midtropospheric vertical shear, which is facilitated by reduced above-PBL static stability in the composite STRONG initial condition. Stronger time-averaged low-to-midtropospheric upward motion coincides with the surface convergence zone in STRONG, and individual CI locations occur at the northeastern edge of the composite vertical motion maximum. Trajectory analysis with STRONG members confirms that the CI locations are consistent with large vertical displacements, and corresponding relative humidity increases leading to decreases in convective inhibition, as the southerly airstream ascends across the convergence zone.

Tectonic deformation in the Santorini volcanic complex (Greece) as inferred by joint analysis of gravity, magnetotelluric and DGPS observations

SUMMARYTectonic activity is very difficult to study in the Santorini volcanic complex (SVC) as it comprises a cluster of small/awkwardly shaped islands covered by pyroclastic deposits from which tell-tale markers are swiftly erased, while seismicity is generally absent. We address the problem by combining geophysical exploration methods to evaluate the long-term effects of tectonic deformation and time-lapse differential GPS to directly evaluate the magnitude and kinematics of present-day deformation. The former comprise 3-D gravity modelling to investigate the footprint of tectonics on the pre-volcanic Alpine basement and natural-field EM induction to map conductivity anomalies epiphenomenal to fluid circulation in faults. Our analysis identified the following principal tectonic elements:The Trans-Santorin Divide (TSD), a segmented NNW–SSE dextral strike-slip fault splitting the SVC sideways of the line joining Cape Exomytis, the Kammeni Islets and the Oia–Therassia Strait. It is collocated with a major vertical conductive zone and forms a series of dents and depressions in the basement. The Columbo Fault Zone (CFZ) is a pair of parallel NE–SW subvertical normal-sinistral faults straddling the northern SVC and terminating against the TSD; it may be associated with fluid injection into the shallow crust but appears to have limited effect on crustal conductivity (compared to TSD). The Anhydros Fault Zone (AFZ) is detected by its footprint on the basement, as a set of parallel northerly dipping NE–SW faults between the Athinios–Monolithos line and Fira. If it has any heave, it is left-lateral. It does not have distinguishable electrical signature and does not contribute to present-day horizontal deformation. The CFZ and AFZ are antithetic and form a graben containing the volcanic centre of Kammeni Islets.E–W extension was identified lengthwise of a zone stretching from Cape Exomytis to Athinios and along the east flank of the caldera to Imerovigli. N–S normal faulting confirmed therein, may have contributed to the localization of the east caldera wall. NNE–SSW compression was observed at SW Thera; this may have produced E-W failure and contributed to the localization of the south caldera wall. The footprint of the caldera on the basement is a parallelogram with N–S long and WNW–ESE short dimensions: if the east and south flanks collapsed along N–S normal and E–W inverse failures, then the west and north flanks may have formed analogously. Present-day deformation is localized on the TSD and CFZ: this can only be explained if the former is the synthetic (dextral) Riedel-R shear and the latter the antithetic (sinistral) Riedel-R′ shear, generated by N–S σ1 and E–W σ3 principal stress axes. Accordingly, NW–SE right-lateral shearing of the broader area is expected and indicated by several lines of indirect evidence. The geographic extent of this shearing and its role in the regional tectonics of the south Aegean remains to be confirmed and appraised by future research.Contemporary volcanic centres develop at the interface of the TSD with the CFZ/AFZ graben; volcanism appears to be controlled by tectonics and the SVC to be shaped by tectonic rather than volcanic activity.

Interseismic Quiescence and Triggered Slip of Active Normal Faults of Kīlauea Volcano's South Flank During 2001–2018

AbstractThe mobile south flank of Kīlauea Volcano hosts two normal fault systems, the Koa'e fault system (KFS) and the Hilina fault system (HFS). In historical time, at least three M>6.5 earthquakes have occurred on the basal detachment of the Kīlauea Volcano's south flank, with the most recent being the 4 May 2018 M6.9 earthquake. Here we analyze kinematic Global Positioning System data collected from 2001 to 2017 and interferometric synthetic aperture radar data before, during, and after the 2018 M6.9 earthquake to determine the crustal motion across the HFS and KFS faults. Our results indicate that the HFS faults did not significantly slip during the interseismic period from 2007 to 2011. Despite its substantial magnitude, interferometric synthetic aperture radar (InSAR) data show that the 2018 M6.9 earthquake triggered subcentimeter level slip along sections of the previously mapped HFS branches. Up to 20 cm of offset occurred on what appears to be a newly formed (or previously unknown) fault near the eastern end of the HFS. During the 3 months following the M6.9 earthquake, up to ~30 cm of slip occurred along the KFS, which helps accommodate rapid large‐scale subsidence of Kīlauea's summit region as large volumes of summit reservoir magma fed the lower East Rift Zone eruption. The HFS appears to activate only in concert with large earthquakes on the basal detachment. The KFS, on the other hand, moves both seismically during small local earthquakes and aseismically in response to nearby earthquakes and caldera subsidence.

A modern analog for meandering rivers of the Mina del Carmen Formation (Albian) at Cañadón Seco oilfield, Golfo San Jorge Basin, Patagonia

Fluvial sandstone reservoirs within the Mina del Carmen Formation (Albian) currently produce up to 10% of the liquid hydrocarbons of the Golfo San Jorge Basin, mainly from isolated channel belts encased in a fine-grained, pyroclastic-rich floodplain. In spite of their economic importance, no modern analogs for the subsurface fluvial reservoirs have been proposed yet, mainly due to the reduced thickness of the channels in relation to the vertical resolution of available 3-D seismic surveys. At Cañadón Seco oilfield (South Flank of the Golfo San Jorge Basin), the planform of a meandering channel belt in Upper Mina del Carmen Formation has been imaged in a 3-D seismic dataset using seismic attributes. The meandering channel belt is up to 13 m thick and 3200 m width, with a sinuosity of 3.61 and has an average channel width of 192 m. Using the measured parameters obtained from the seismic dataset, we tested the applicability of empirical relations developed for modern rivers; the results of the statistical equations showed a close correspondence with seismic measurements and allowed us to estimate data of formative river discharge and upstream catchment area for the subsurface example. Both values were then parallel with a database of river discharge and area of up to 1018 hydrometeorological stations in drainage catchments around the world. Nine rivers of the database show discharge-area values comparable to those obtained using empirical equations. After a review of satellite imagery of the nine areas, a modern analog for the subsurface example was found in the Middle Ebro River (Spain). The analog consists of a meandering fluvial depositional system in a foreland basin setting, with seasonal discharge variability. The approach followed in the research can be of use to any fluvial basin, but considering that fluvial systems are highly variable in scale, geometry, pattern and composition, the extrapolation of results to other regions or even to other strata within the Mina del Carmen Formation, should be done with caution.