Episodic earthquake mechanisms and intervening seismicity during the 2018 summit collapse at Kilauea caldera

<p>The 2018 rift zone eruption of Kilauea volcano was accompanied by a remarkable and episodic collapse of its summit. Between May-August the eruption and collapse sequence included over 70,000 earthquakes (M≥0) and 54 major earthquakes (M≥5). We analyzed the seismicity in the Kilauea summit region and estimated seismic full moment tensors with their uncertainties for the 54 M≥5 events. These events occurred at almost daily intervals and were accompanied by intense seismicity which was concentrated between 0-3 km depths beneath the Halema‘uma‘u pit crater. The hypocenters reveal partial elliptical patterns (map view) that migrated downward by ∼200 m. The moment tensors reveal remarkably consistent mechanisms, with negative isotropic source types and localized uncertainties, and vertical P-axis orientations. From the moment tensors we derived Poisson’s ratios which are variable (ν = 0.1 − 0.3) for the first half of the collapse events and converged to ν ∼ 0.28 from June 26 onward.</p>

Interplay of volcanotectonic, sedimentary, and regional tectonic processes at Mount Etna’s submerged south-eastern flank

<p><span>Collapses of coastal and ocean island volcanoes can cause damaging tsunamis and thus pose ocean-wide hazards. To assess the collapse hazard of an unstable flank, a profound understanding of its structural setting and active deformation is essential. This knowledge is, however, often missing, especially for the remote and submerged offshore part of the edifice. Long before satellite-based techniques were available, observations of extensional structures in the summit region and transpressive to compressional structures farther downslope helped to constrain flank instability onshore at many volcanoes globally. Similar deformation structures are also expected offshore where they might be even better preserved due to the absence of anthropogenic influence, limited weathering and erosion. However, in the offshore realm structures related to flank instability are masked by and interact with other processes that act on underwater slopes, such as bottom currents, downslope sediment transport, and regional tectonics. Furthermore, the remote location of offshore flanks complicates geophysical, geomorphological, and geological investigations. Using (micro-) bathymetric and high-resolution seismic data we analyse the seascape forming processes at the Eastern Sicily continental slope at the foot of Mount Etna's unstable south-eastern flank. We untangle seafloor structures related to volcanotectonic, sedimentary, and regional tectonic processes. This allows singling out patterns and structures related to volcano flank instability, such as the lateral and outward boundaries of the unstable flank. We identify a strike-slip fault that changes its morphological appearance from a sharp linear feature atop a pressure ridge north of Catania Canyon to an almost smooth seafloor further downslope, where gravitational sediment transport outbeats volcanotectonic activity. Sediment transport from the continent to the abyss occurs along several canyons and channels that partly align with fault systems. Furthermore, uplift at the distant toe of Etna‘s south-eastern flank may indicate compression from the downwards moving flank, while at the same time provoking erosional responses, e.g. landslides. This new information provides important constraints for kinematic models that seek to explain the drivers of flank instability. It also forms the base for future studies that will infer the styles and rates of offshore flank deformation from the geological record. </span></p>

Micro-bathymetric mapping of the North Alfeo strike-slip fault (offshore Catania Sicily): preliminary results from the FocusX1 expedition

<p>In October 2020, during the marine expedition FocusX1 onboard the research vessel PourquoiPas? microbathymetric mapping was performed using the ROV Victor6000. The main goal was to map the seafloor expression of the North Alfeo fault and select the best path for deployment of a 6-km long fiber optic strain cable designed to monitor movement along the fault and the deployment sites for 8 geodetic stations.</p><p>Bathymetric data were collected through a Reson Seabat 7125 multibeam echosounder (400 kHz). ROV navigation data were processed using DelphINS, resulting in an optimal merging of navigation sensors (GPS, USBL, DVL, pressure). The MBES data processing (GLOBE software) mainly consisted in estimating and correcting static angular offsets, applying actual in-situ sound speed profile, and finally performing an automatical and manual soundings filtering.</p><p>The resulting bathymetric grid spans a region of roughly 3 km x 1.5 km, with a 1m cell size, and allows  us to identify a variety of morphological features:</p><p>1 - a set of narrow, linear, E-W oriented gulleys, all parallel (not merging/branching) on a regional E dipping 5-15° slope</p><p>2 - a striking, continuous curvi-linear feature, which is interpreted as the primary surface expression of the fault.The fault morphology changes from a smooth less than 10 m depression in the NW to a up to 10-20m high scarp with slopes of 20-30°, and locally sub-vertical cliff faces.</p><p>3 - a local bathymetric plateau (mesa like feature) with a gently E-dipping summit region, showing signs of eastward sliding / rafting tectonics, indicated by N-S oriented gashes/depressions.</p><p>The 3-km long segment of the fault covered by our survey includes the mesa-like bathymetric high (at the NW extremity) interpreted as a transpressional pop-up feature and an elongated, fault bounded trough (at the SE extremity) interpreted as a transtensional pull-apart basin. Video-camera images recorded by ROV Victor6000 from the seafloor provide visual documentation of the fault scarp and seafloor morphology. Future surveys with a sub-bottom profiler and/or HR- seismics can help confirm these interpretations. The ongoing monitoring with the fiber-optic strain cable is being calibrated by a 3-4 year deployment of seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) which started in Oct. 2020, and will allow us to quantify relative displacement across the fault.</p>

Machine learning based detection of volcano seismicity using the spatial pattern of amplitudes

Summary We propose a new algorithm, focusing on spatial amplitude patterns, to automatically detect volcano seismic events from continuous waveforms. Candidate seismic events are detected based on signal-to-noise ratios. The algorithm then utilizes supervised machine learning to classify the existing candidate events into true and false categories. The input learning data are the ratios of the number of time samples with amplitudes greater than the background noise level at 1 s intervals (large amplitude ratios) given at every station site, and a manual classification table in which ‘true'' or ‘false'' flags are assigned to candidate events. A two-step approach is implemented in our procedure. First, using the large amplitude ratios at all stations, a neural network model representing a continuous spatial distribution of large amplitude probabilities is investigated at 1 s intervals. Second, several features are extracted from these spatial distributions, and a relation between the features and classification to true and false events is learned by a support vector machine. This two-step approach is essential to account for temporal loss of data, or station installation, movement, or removal. We evaluated the algorithm using data from Mt. Ontake, Japan, during the first ten days of a dense observation trial in the summit region (November 1–10, 2017). Results showed a classification accuracy of more than 97 per cent.

History and Data Records of the Automatic Weather Station on Denali Pass (5715 m), 1990–2007

We present the data records and station history of an automatic weather station (AWS) on Denali Pass (5715 m MSL), Alaska. The station was installed by a team of climbers from the Japanese Alpine Club after a fatal accident involving Japanese climbers in 1989 and was operational intermittently between 1990 and 2007, measuring primarily air temperature and wind speed. In later years, the AWS was operated by the International Arctic Research Center of the University of Alaska Fairbanks. Station history is reconstructed from available documentation as archived by the expedition teams. To extract and preserve data records, the original datalogger files were processed. We highlight numerous challenges and sources of uncertainty resulting from the location of the station and the circumstances of its operation. The data records exemplify the harsh meteorological conditions at the site: air temperatures down to approximately −60°C were recorded, and wind speeds reached values in excess of 60 m s−1. Measured temperatures correlate strongly with reanalysis data at the 500-hPa level. An approximation of critical wind speed thresholds and a reanalysis-based reconstruction of the meteorological conditions during the 1989 accident confirm that the climbers faced extremely hazardous wind speeds and very low temperatures. The data from the Denali Pass AWS represent a unique historical record that can, we hope, serve as a basis for further monitoring efforts in the summit region of Denali.

The Mountain Weather and Climate of Denali, Alaska—An Overview

An overview of climatological and meteorological conditions and their seasonal variability in the Denali summit region is presented, based on the NCEP–NCAR reanalysis 1 dataset for the 1948–2018 period. At the Denali grid cell, a warming trend of +0.02°C significant at the 95% level is found—equivalent to a temperature increase of 1.4°C over the time period. The number of very cold days (<−35°C) during the climbing season (April–July) has decreased by approximately a day per decade. The number of very windy days (≥20 m s−1) during the climbing season also shows a decreasing trend for the majority of the time series. To assess synoptic patterns that affect the Denali region, a self-organizing map algorithm was applied to the geopotential height (GPH) field extracted from the reanalysis data. In winter, the synoptic situation in the Denali region is dominated by frequent zonal flow and negative GPH anomalies associated with the polar front. As the polar front moves north during the seasonal cycle, patterns shift to largely positive GPH anomalies and more meridional flow. Extreme wind speeds unfavorable for climbing occur in all seasons and are associated mainly with the polar jet passing directly over Denali, or cyclogenesis in the Bering Sea. The frequency of occurrence of strongly zonal, low GPH patterns during the main climbing season (April–July) shows a slight decrease in recent years.

Dynamics of the 1989 fracture system and relations with the Etna eruptive activity of the last 30 years

&lt;p&gt;On September 11, 1989, after four months of Strombolian activity at the summit craters, effusive activity began on Mt. Etna and lasted about a month.&lt;/p&gt;&lt;p&gt;The 1989 eruption of Mt. Etna was characterized by the formation of two fracture systems, striking NE-SW and NNW-SSE, and both starting from the SE Crater on September, 24.&lt;/p&gt;&lt;p&gt;The NE-SW system was followed by effusive activity while the NNW-SSE fractures opened for a length of 7 km without eruptive phenomena. Between September, 27 and October, 3 the fracture system propagated until it reached and cut the SP 92 provincial road (Zafferana - Rifugio Sapienza), near the 1792 effusive mouth, and continued southward for another 700 m.&lt;/p&gt;&lt;p&gt;We investigated the fracture southern branch dynamics through 30 years of ground deformation data collected by the discrete and continuous INGV monitoring networks. We considered levelling, GPS, EDM, and extensometers data. EDM and levelling measurements began in the 80s; on 2003 EDM measurements have been replaced by GPS.&lt;/p&gt;&lt;p&gt;During the 1989 eruption, EDM measurements showed variations of tens of centimeters on the lines close to the fracture.&lt;/p&gt;&lt;p&gt;Precise levelling discrete measurements revealed, in the period 4-16 October 1989 and during the 1991-1993 eruption a subsidence of some centimeters on benchmarks close to fracture.&lt;/p&gt;&lt;p&gt;A network of rod extensometers evidenced the fracture activation during the 2001 intrusion phases (12-17 July) measuring several centimeters of left lateral slip. Distance measurements and InSAR show signs of the fracture reactivation during the 2002 and 2018 eruptions.&lt;/p&gt;&lt;p&gt;Several authors show as the 1989 fracture zone connects the summit region of the volcano with the tectonic structures of the lower SE flank considering it as well part of the NNW-SSE oriented structure.&lt;/p&gt;&lt;p&gt;The dynamics of these last 30 years suggests that the 1989 fracture play an important role on the flank dynamics and strain distribution. It also represents a potential hazard to population because it represents a possible way of ascending magma also testified by cones aligned along the structure.&lt;/p&gt;