Understanding physical processes prior to and during volcanic eruptions has improved significantly in recent years. However, uncertainties about subsurface structures distorting observed signals and ...undetected processes within the volcano prevent volcanologists to infer subtle triggering mechanisms of volcanic phenomena. Here, we demonstrate that distributed acoustic sensing (DAS) with optical fibres allows us to identify volcanic events remotely and image hidden near-surface volcanic structural features. We detect and characterize strain signals associated with explosions and locate their origin using a 2D-template matching between picked and theoretical wave arrival times. We find evidence for non-linear grain interactions in a scoria layer of spatially variable thickness. We demonstrate that wavefield separation allows us to incrementally investigate the ground response to various excitation mechanisms. We identify very small volcanic events, which we relate to fluid migration and degassing. Those results provide the basis for improved volcano monitoring and hazard assessment using DAS.
Natural hazard prediction and efficient crust exploration require dense seismic observations both in time and space. Seismological techniques provide ground-motion data, whose accuracy depends on ...sensor characteristics and spatial distribution. Here we demonstrate that dynamic strain determination is possible with conventional fibre-optic cables deployed for telecommunication. Extending recently distributed acoustic sensing (DAS) studies, we present high resolution spatially un-aliased broadband strain data. We recorded seismic signals from natural and man-made sources with 4-m spacing along a 15-km-long fibre-optic cable layout on Reykjanes Peninsula, SW-Iceland. We identify with unprecedented resolution structural features such as normal faults and volcanic dykes in the Reykjanes Oblique Rift, allowing us to infer new dynamic fault processes. Conventional seismometer recordings, acquired simultaneously, validate the spectral amplitude DAS response between 0.1 and 100 Hz bandwidth. We suggest that the networks of fibre-optic telecommunication lines worldwide could be used as seismometers opening a new window for Earth hazard assessment and exploration.
Merapi volcano (Indonesia) is one of the most active and hazardous volcanoes in the world. It is known for frequent small to moderate eruptions, pyroclastic flows produced by lava dome collapse, and ...the large population settled on and around the flanks of the volcano that is at risk. Its usual behavior for the last decades abruptly changed in late October and early November 2010, when the volcano produced its largest and most explosive eruptions in more than a century, displacing at least a third of a million people, and claiming nearly 400 lives. Despite the challenges involved in forecasting this ‘hundred year eruption’, we show that the magnitude of precursory signals (seismicity, ground deformation, gas emissions) was proportional to the large size and intensity of the eruption. In addition and for the first time, near-real-time satellite radar imagery played an equal role with seismic, geodetic, and gas observations in monitoring eruptive activity during a major volcanic crisis. The Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) issued timely forecasts of the magnitude of the eruption phases, saving 10,000–20,000 lives. In addition to reporting on aspects of the crisis management, we report the first synthesis of scientific observations of the eruption. Our monitoring and petrologic data show that the 2010 eruption was fed by rapid ascent of magma from depths ranging from 5 to 30km. Magma reached the surface with variable gas content resulting in alternating explosive and rapid effusive eruptions, and released a total of ~0.44Tg of SO2. The eruptive behavior seems also related to the seismicity along a tectonic fault more than 40km from the volcano, highlighting both the complex stress pattern of the Merapi region of Java and the role of magmatic pressurization in activating regional faults. We suggest a dynamic triggering of the main explosions on 3 and 4 November by the passing seismic waves generated by regional earthquakes on these days.
► First scientific results from largest eruption in 100years of Merapi volcano. ► Gas emissions were much higher than recorded at Merapi during past eruptions. ► Deep influx of gas-rich mafic magma triggered the eruption. ► Presence of an exsolved fluid phase co-existent with the pre-eruptive magma body. ► Eruption warnings by CVGHM and international team saved 10,000–20,000 lives.
Type of PKD1 Mutation Influences Renal Outcome in ADPKD LE GALL, Emilie Cornec; AUDREZET, Marie-Pierre; GUILLODO, Marie-Paule ...
Journal of the American Society of Nephrology,
06/2013, Volume:
24, Issue:
6
Journal Article
Peer reviewed
Open access
Autosomal dominant polycystic kidney disease (ADPKD) is heterogeneous with regard to genic and allelic heterogeneity, as well as phenotypic variability. The genotype-phenotype relationship in ADPKD ...is not completely understood. Here, we studied 741 patients with ADPKD from 519 pedigrees in the Genkyst cohort and confirmed that renal survival associated with PKD2 mutations was approximately 20 years longer than that associated with PKD1 mutations. The median age at onset of ESRD was 58 years for PKD1 carriers and 79 years for PKD2 carriers. Regarding the allelic effect on phenotype, in contrast to previous studies, we found that the type of PKD1 mutation, but not its position, correlated strongly with renal survival. The median age at onset of ESRD was 55 years for carriers of a truncating mutation and 67 years for carriers of a nontruncating mutation. This observation allows the integration of genic and allelic effects into a single scheme, which may have prognostic value.
•EGS seismicity is compared to wastewater disposal and ultra-deep fluid-injection events.•Near-well and far-field fracturing mechanisms are identified in EGS stimulation.•Recommendations are given to ...safely operate EGS sites (seismic hazard).
In this overview we report results of analysing induced seismicity in geothermal reservoirs in various tectonic settings within the framework of the European Geothermal Engineering Integrating Mitigation of Induced Seismicity in Reservoirs (GEISER) project. In the reconnaissance phase of a field, the subsurface fault mapping, in situ stress and the seismic network are of primary interest in order to help assess the geothermal resource. The hypocentres of the observed seismic events (seismic cloud) are dependent on the design of the installed network, the used velocity model and the applied location technique. During the stimulation phase, the attention is turned to reservoir hydraulics (e.g., fluid pressure, injection volume) and its relation to larger magnitude seismic events, their source characteristics and occurrence in space and time. A change in isotropic components of the full waveform moment tensor is observed for events close to the injection well (tensile character) as compared to events further away from the injection well (shear character). Tensile events coincide with high Gutenberg-Richter b-values and low Brune stress drop values. The stress regime in the reservoir controls the direction of the fracture growth at depth, as indicated by the extent of the seismic cloud detected. Stress magnitudes are important in multiple stimulation of wells, where little or no seismicity is observed until the previous maximum stress level is exceeded (Kaiser Effect). Prior to drilling, obtaining a 3D P-wave (Vp) and S-wave velocity (Vs) model down to reservoir depth is recommended. In the stimulation phase, we recommend to monitor and to locate seismicity with high precision (decametre) in real-time and to perform local 4D tomography for velocity ratio (Vp/Vs). During exploitation, one should use observed and model induced seismicity to forward estimate seismic hazard so that field operators are in a position to adjust well hydraulics (rate and volume of the fluid injected) when induced events start to occur far away from the boundary of the seismic cloud.
The Reykjanes Geothermal System (RGS) is a high‐temperature geothermal system located on the Reykjanes peninsula, a transtensional plate‐boundary zone located on the southwestern tip of Iceland. The ...area is characterized by high seismicity, recent volcanism, and high‐temperature geothermal fields. We use seismic noise records from April 2014 to August 2015 to study stress changes and potential deformation of the subsurface caused by injection and production operations at RGS through seismic interferometry. We retrieve continuous time series of waveform similarity values and seismic velocity changes during this period. The S‐transform of the similarity values allows us to clearly identify three variations in the mechanical properties of the Reykjanes peninsula related to rapid changes of RGS production. In addition, we observe a slow seismic velocity decrease of 0.36%/year in the reservoir due to the water deficit and seasonal variations associated with the energy production demand.
Plain Language Summary
The Mid‐Atlantic Spreading Ridge divides the Reykjanes peninsula into two tectonic plates and causes the high volcanic activity that characterizes the area. The Reykjanes Geothermal System is one of the five high‐temperature geothermal systems exploited in this peninsula. The energy production of Reykjanes Geothermal System has been increasing, causing drastic changes in reservoir conditions, such as, a man‐made subsidence of around 10 cm in the area. We employ three current methodologies to monitor changes of mechanical and structural properties in the subsurface, using 1.5 years of continuous seismic records. We identify and locate three short‐term variations associated with abrupt injection and production rate changes in Reykjanes Geothermal System. In addition, we observe a slow seismic velocity decrease due to the long‐term water extraction, as well as variations associated with demand‐driven seasonal fluctuations in the extraction rates.
Key Points
Identification of three elastic properties changes in time‐frequency associated with abrupt injection and production rate variations
Water deficit in the reservoir leads to a gradual seismic velocity decrease
Seasonal production rate variations within the geothermal reservoir are observed as structural property changes
White Island volcano, New Zealand, produced two periods (January–February and July 2013) of episodic and persistent eruptions through a viscous shallow mud/sulphur pool. The eruptions included an ...initial hemispherical bubble burst, which was intermittently followed by an up-channel gas jet, and finally a late stage heaving of a mud/sulphur/water suspension. The late stage heave was systematically directed south-eastward as far as 30–40m from the vent.
The associated infrasound time-series included harmonic tremor on permanent stations WIZ and WSRZ. Detailed inspection showed that the tremor was composed of numerous discrete double pulse events without a strong periodic event repetition. The first pulse had highly similar waveforms event-to-event and a notable distortion of the waveform period between the two infrasound stations located on opposites sides from the directed eruption source. The second pulse occurred about 1.5–2.5s later and was weakly observed on station WSRZ.
Where the video can be rigorously linked to the double pulse infrasound signals we interpret aspects of the distinctive eruptive regimes. For this case, the regime dynamics are driven by the propagation of numerous discrete gas slugs though the shallow viscous muddy crater lake, each generating a distinct bubble burst with subsequent eruption heave and associated double pulse infrasound events. The double pulse events are the source of the persistent harmonic tremor having fundamental and overtone spectral frequencies but are not interpreted as related to cavity resonance or a repetitious comb function. Instead the activity is produced by a single event producing a specific two pulse source time function. The observed distortion in the first pulse wave period at WIZ and WSRZ may be ascribed to a Doppler shift associated with the directivity observed in the initial jet/heave eruption process. We surmise that double pulse source dynamics and directivity effects may be generically extended to some examples of subsurface seismic tremor or for tremor associated with geyser eruptions, mud volcano eruptions, fire fountains from lava lakes and strombolian eruptions.
•Infrasound tremor observed during periods of persistent bubble bursts through viscous shallow Crater Lake.•Infrasound double pulse source dynamics are linked to gas slug burst dynamics.•Observed directivity of eruptions are consistent with Doppler shift observed at infrasound sensors.•Harmonic tremor may be produced without comb function or resonant cavity.
A letter to the doctor Jules Cloquet, written in Cairo, is chosen as a sample of Flaubert’s correspondence in the 1850’s. Representative of what is called the “average” epistolary writing, it can be ...used as a negative to understand to what extent the novelist engaged in self-mutilation so as to “faire oeuvre” by perfecting the art of prose that has brought him so much praise. The major issues is that by becoming a totem Flaubert’s style has given literature and its teaching in France a decisive orientation, of which today’s debates show the historicity.
Distributed Dynamic Strain Sensing (DDSS), also known as Distributed Acoustic Sensing (DAS), is becoming a popular tool in array seismology. A new generation of engineered fibers is being developed ...to improve sensitivity and reduce the noise floor in comparison to standard fibers, which are conventionally used in telecommunication networks. Nevertheless, standard fibers already have extensive coverage around the Earth's surface, so it motivates the use of the existing infrastructure in DDSS surveys to avoid costs and logistics. In this study, we compare DDSS data from stack instances of standard multi-fiber cable with DDSS data from a co-located single-fiber engineered cable. Both cables were buried in an area located 2.5 km NE from the craters of Mt. Etna. We analyze how stacking can improve signal quality. Our findings indicate that the stack of DDSS records from five standard fiber instances, each 1.5 km long, can reduce optical noise of up to 20%. We also present an algorithm to correct artifacts in the time series that stem from dynamic range saturation. Although stacking is able to reduce optical noise, it is not sufficient for restoring the strain-rate amplitude from saturated signals in standard fiber DDSS. Nevertheless, the algorithm can restore the strain-rate amplitude from saturated DDSS signals of the engineered fiber, allowing us to exceed the dynamic range of the record. We present measurement strategies to increase the dynamic range and avoid saturation.
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