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Results for “The Seismic Record”

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At least 1,513 records · Page 84Linked to original sources
USGS2023

Identification of seismo-volcanic regimes at Whakaari/White Island (New Zealand) via systematic tuning of an unsupervised classifier

We present an algorithm based on Self-Organizing Maps (SOM) and k-means clustering to recognize patterns in a continuous 12.5-year tremor time series recorded at Whakaari/White Island volcano, New Zealand (hereafter referred to as Whakaari). The approach is extendable to a variety of volcanic settings through systematic tuning of the classifier. Hyperparameters are evaluated by statistical means, yielding a combination of “ideal” SOM parameters for the given data set. Extending from this, we applied a Kernel Density Estimation approach to automatically detect changes within the observed seismicity. We categorize the Whakaari seismic time series into regimes representing distinct volcano-seismic states during recent unrest episodes at Whakaari (2012/2013, 2016, and 2019). There is a clear separation in classification results between background regimes and those representing elevated levels of unrest. Onset of unrest is detected by the classifier 6 weeks before the August 2012 eruption, and ca. 3.5 months before the December 2019 eruption, respectively. Regime changes are corroborated by changes in commonly monitored tremor proxies as well as with reported volcanic activity. The regimes are hypothesized to represent diverse mechanisms including: system pressurization and depressurization, degassing, and elevated surface activity. Labeling these regimes improves visualization of the 2012/2013 and 2019 unrest and eruptive episodes. The pre-eruptive 2016 unrest showed a contrasting shape and nature of seismic regimes, suggesting differing onset and driving processes. The 2016 episode is proposed to result from rapid destabilization of the shallow hydrothermal system, while rising magmatic gases from new injections of magma better explain the 2012/2013 and 2019 episodes.

Whakaari, White Island↗
USGS2003

High-resolution lidar topography of the Puget Lowland, Washington - A bonanza for earth science

More than 10,000 km2 of high-resolution, public-domain topography acquired by the Puget Sound Lidar Consortium is revolutionizing investigations of active faulting, continental glaciation, landslides, and surficial processes in the seismically active Puget Lowland. The Lowland-the population and economic center of the Pacific Northwest-presents special problems for hazards investigations, with its young glacial topography, dense forest cover, and urbanization. Lidar mapping during leaf-off conditions has led to a detailed digital model of the landscape beneath the forest canopy. The surface thus revealed contains a rich and diverse record of previously unknown surface-rupturing faults, deep-seated landslides, uplifted Holocene and Pleistocene beaches, and subglacial and periglacial features. More than half a dozen suspected postglacial fault scarps have been identified to date. Five scarps that have been trenched show evidence of large, Holocene, surface-rupturing earthquakes.

GSA Today↗
USGS1985

A general earthquake-observation system (GEOS)

Microprocessor technology has permitted the development of a General Earthquake-Observation System (GEOS) useful for most seismic applications. Central-processing-unit control via robust software of system functions that are isolated on hardware modules permits field adaptability of the system to a wide variety of active and passive seismic experiments and straightforward modification for incorporation of improvements in technology. Various laboratory tests and numerous deployments of a set of the systems in the field have confirmed design goals, including: wide linear dynamic range (16 bit/96 dB); broad bandwidth (36 hr to 600 Hz; greater than 36 hr available); selectable sensor-type (accelerometer, seismometer, dilatometer); selectable channels (1 to 6); selectable record mode (continuous, preset, trigger); large data capacity (1. 4 to 60 Mbytes); selectable time standard (WWVB, master, manual); automatic self-calibration; simple field operation; full capability to adapt system in the field to a wide variety of experiments; low power; portability; and modest costs. System design goals for a microcomputer-controlled system with modular software and hardware components as implemented on the GEOS are presented. The systems have been deployed for 15 experiments, including: studies of near-source strong motion; high-frequency microearthquakes; crustal structure; down-hole wave propagation; teleseismicity; and earth-tidal strains.

Bulletin of the Seismological Society of America↗
USGS1989

Use of surface-geophysical methods to assess riverbed scour at bridge piers

A ground-penetrating-radar system, and three seismic systems--color fathometer, tuned transducer, and black-and-white fathometer--were used to evaluate river-bed scour at the Charter Oak, Founder 's and Bulkeley Bridges in Hartford, Connecticut. Cross-sections of the channel and some lateral sections were run at each bridge in June and July 1987, and significant scour at piers supporting each of these bridges was recorded. Each of the four geophysical systems proved to have advantages and limitations. The ground penetrating radar system used single and dual 80 megahertz antennae floating in the water to transmit and receive the signal. The method was successful in water less than 25 ft deep, and in resistive earth materials. The geometry of existing scour holes and the extent of post-scour sedimentation were clearly defined. The color fathometer, operating at a signal frequency of 20 kilohertz, delineated existing scour-hole geometry, detected infilling of scour holes, and provided qualitative information about the physical properties of sediments. The tuned transducer, operating at a signal frequency of 14 kilohertz, defined scour-hole geometry and the extent of post-scour sediment deposition. Both of these systems were effective in water greater than 5 ft deep. At a signal frequency of 200 kilohertz, the black-and-white fathometer could not penetrate post-scour deposits, but it was useful in defining existing scour-holed geometry in water of any depth. (USGS)

Water-Resources Investigations Report↗
USGS2020

Observations of an extreme atmospheric river storm with a diverse sensor network

Observational networks enhance real‐time situational awareness for emergency and water resource management during extreme weather events. We present examples of how a diverse, multitiered observational network in California provided insights into hydrometeorological processes and impacts during a 3‐day atmospheric river storm centered on 14 February 2019. This network, which has been developed over the past two decades, aims to improve understanding and mitigation of effects from extreme storms influencing water resources and natural hazards. We combine atmospheric reanalysis output and additional observations to show how the network allows: (1) the validation of record cool season precipitable water observations over southern California; (2) the identification of phenomena that produce natural hazards and present difficulties for short‐term weather forecast models, such as extreme precipitation amounts and snow level variability; (3) the use of soil moisture data to improve hydrologic model forecast skill in northern California's Russian River basin; and (4) the combination of meteorological data with seismic observations to identify when a large avalanche occurred on Mount Shasta. This case study highlights the value of investments in diverse observational assets and the importance of continued support and synthesis of these networks to characterize climatological context and advance understanding of processes modulating extreme weather.

California↗
USGS2020

Estimating rupture dimensions of three major earthquakes in Sichuan, China, for early warning and rapid loss estimates

Large earthquakes like in Wenchuan in 2008, MW 7.9, Sichuan, China, provide opportunity for earthquake early warning (EEW) as many heavily shaken areas are far (~50 km) from the epicenter and warning time could be long enough (≥ 5 s) to take effective preventative action. On the other hand, earthquakes with magnitudes larger than ~M 6.5 are challenging for EEW since source dimensions need to be defined in order to adequately estimate shaking. The Finite-Fault Rupture Detector (FinDer) is an approach to identify fault rupture extents from real-time strong motion and/or broadband records. In this study, we playback local and regional on-scale strong motion waveforms recorded during the 2008 MW 7.9 Wenchuan, 2013 MW 6.6 Lushan, and 2017 MW 6.5 Jiuzhaigou earthquakes to study the performance of FinDer for the current layout of the China Strong Motion Network. Overall, the FinDer line-source models agree well with the observed spatial distribution of aftershocks and fault models determined from waveform inversion. However, since FinDer models are constructed to characterize seismic ground motions (as needed for EEW) instead of source parameters, the rupture length can be overestimated for events radiating high levels of high-frequency motions, as is the case in the Lushan earthquake. If the set of strong motion data used had been available in real-time, 50% to 80% of sites experiencing shaking of intensity MMI IV-VII (light to very strong) and 30% experiencing VIII-IX (severe to violent) could have been issued a warning with 10 s and 5 s, respectively, before the arrival of the destructive S-wave. We also show that loss estimates after devastating earthquakes based on the FinDer line-source are more accurate compared to a point-source model. For the Wenchuan earthquake, for example, they predict a four to six times larger number of fatalities and injured, which is consistent with official reports. At the same time, these losses could be provided 1/2~3 hours faster than if based on more complex inversion rupture models.

Sichuan↗
USGS2024

Empirical ground-motion basin response in the California Great Valley, Reno, Nevada, and Portland, Oregon

We assess how well the Next-Generation Attenuation-West 2 (NGA-West2) ground-motion models (GMMs), which are used in the US Geological Survey’s (USGS) National Seismic Hazard Model (NSHM) for crustal faults in the western United States, predict the observed basin response in the Great Valley of California, the Reno basin in Nevada, and Portland and Tualatin basins in Oregon. These GMMs rely on site parameters such as the time-averaged shear-wave velocity ( V S ) in the upper 30 m of Earth’s crust ( V S30 ) and depths to 1.0 and 2.5 km/s shear-wave isosurfaces ( Z 1.0 and Z 2.5 ) to capture basin effects and were developed using observations and simulations primarily from the Los Angeles region in southern California. Using ground-motion records from mostly small-to-moderate earthquakes and mixed-effects regression analysis, we find that the GMMs perform well with our local basin-depth models for the California Great Valley. With our local basin-depth models for Reno, the GMMs do not perform as well for this relatively shallow basin and exhibit little sensitivity to the basin parameters used in the NGA-West2 GMMs. We also find good performance for the local Z 1.0 model across the Portland region, whereas the local Z 2.5 model provides little predictive power except at sites in the deepest part of the Tualatin basin. Additional work could improve the performance of the site and basin terms in the NGA-West2 GMMs for regions with geologic structure different than the deep basins in southern California and the Great Valley. In addition, we find significant discrepancies among the GMMs in how the uncertainty in the ground motion varies with basin depth and pseudospectral period. Our results can help guide seismic hazard analyses on whether to include these local basin-depth models.

Earthquake Spectra↗
USGS2001

Observations of basin ground motions from a dense seismic array in San Jose, California

We installed a dense array of 41 digital seismographs in San Jose, California, to evaluate in detail the effects of a deep sedimentary basin and shallow sedimentary deposits on earthquake ground motions. This urban array is located near the eastern edge of the Santa Clara Valley and spans the Evergreen sedimentary basin identified by gravity data. Average station spacing is 1 km, with three stations initially spaced 110 m apart. Despite the high-noise urban environment, the stations of the array successfully triggered on and recorded small local earthquakes (M 2.5-2.8 at 10-25 km distance) and larger regional events such as the M 5.0 Bolinas earthquake (90 km distance), M 4.6-5.6 earthquakes near Mammoth Lakes (270 km distance), M 4.9-5.6 events in western Nevada (420 km distance) and the M 7.1 Hector Mine earthquake (590 km distance). Maps of spectral ratios across the array show that the highest amplitudes in all frequency bands studied (0.125-8 Hz) are generally observed at stations farther from the eastern edge of the Santa Clara Valley. Larger spectral amplitudes are often observed above the western edge of the Evergreen Basin. Snapshots of the recorded wavefield crossing the array for regional events to the east reveal that large, low-frequency (0.125-0.5 Hz) arrivals after the S-wave travel from south to north across the array. A moving-window, cross-correlation analysis finds that these later arrivals are surface waves traveling from the south. The timing and propagation direction of these arrivals indicates that they were likely produced by scattering of incident S waves at the border of the Santa Clara Valley to the south of the array. It is remarkable that the largest low-frequency phases at many of the valley sites for regional events to the east are basin surface waves coming from a direction about 70 degrees different from that of the epicenters. Basin surface waves emanating from the eastern edge of the valley are also identified by the cross-correlation analysis.

Bulletin of the Seismological Society of America↗
USGS2006

Introduction to ‘Antarctic climate evolution: View from the margin’

This special issue on “Antarctic Climate Evolution—view from the margin” presents results from modelling studies and reports on geoscience data aimed at improving our understanding of the behaviour of the Antarctic ice sheet and the climate of the region. This research field is of interest because of the sensitivity of the polar regions to global warming, and because of the influence of the Antarctic ice sheet on global sea level and climate through most if not all of the Cenozoic Era. The Antarctic ice sheet both responds to and forces changes on global climate and sea level. We need to be aware of the scale and frequency of these changes if we are to understand past patterns of environmental change elsewhere on earth. It was only three decades ago that we discovered from strata drilled in shelf basins on the Antarctic margin that the Antarctic ice sheet had a history that predated the Quaternary ice ages by over 20 million years ( Hayes et al., 1975 ). Later that year the first interpretation of Antarctic glacial history through the Cenozoic Era from oxygen isotopes, recorded in foraminifera from deep-sea sediment cores, was published ( Shackleton and Kennett, 1975 ). Revisions with a more extensive database have modified the story a little ( Miller et al., 1987 , Zachos et al., 2001 ), and there have been recent attempts to resolve the temperature–ice volume ambiguity ( Lear et al., 2000 ). However, reports on strata drilled on the Antarctic margin have unambiguously shown the character of this huge ice sheet, which was oscillating in the Oligocene ( Barrett et al., 1987 , Barrett, 1999 ) with a period and magnitude comparable with the Northern Hemisphere ice sheets of the Quaternary ( Naish et al., 2001a , Naish et al., 2001b ). In this issue we present further research on the history of the Antarctic ice sheet from Oligocene to recent times, most of them from the Antarctic margin, but with some on the nature of the deep-sea isotope record, and others using recently developed modeling techniques to investigate the influence of atmosphere, ocean and biosphere on past Antarctic climate. This special issue is the third in three years on the theme of Antarctic Climate Evolution. The first followed a workshop in Erice, Sicily, in 2001 to report on results from ANTOSTRAT, a SCAR-sponsored project for gathering and analysing circum-Antarctic seismic data for planning and promoting offshore drilling for climate history. The introduction to that issue (Florindo et al., 2003) provides a review of the recent history of circum-Antarctic drilling by the Ocean Drilling Program (Legs 113, 114, 119, 120, 177, 178, 188 and 189) and the Cape Roberts Project. For a more comprehensive review of earlier drilling in the Ross Sea region (Deep Sea Drilling Project Leg 28, Dry Valley Drilling Project, McMurdo Sound Sediment and Tectonic Studies, Cenozoic Investigations in the western Ross Sea) see Hambrey and Barrett (1993). The first of these issues (Florindo et al., 2003) featured a global plate reconstruction of the Southern Hemisphere through Cenozoic time with emphasis on evolution of Cenozoic seaways (Lawver and Gahagan, 2003) along with a study of the inception and early evolution of the EAIS using a new coupled global climate (GCM)–dynamic ice sheet model (DeConto and Pollard, 2003b), as well as data from recent drilling around the margin covering time period from Cretaceous to the present. A second special issue on the same theme (Florindo et al., 2005) also featured a mix of modelling and data papers with a focus on the Eocene–Oligocene boundary and the initiation of ice sheet growth, including a pioneering attempt to evaluate the relative influence of fluvial versus glacial processes in shaping the landscape of the Prydz Bay sector of Antarctica (Jamieson et al., 2005). The remainder of the issue comprised further papers on seismic stratigraphy and reports from drilling around the margin. The papers to be found in this special issue, like the previous two, maintain the mix of modelling- and data-oriented papers that reflect the range of this research.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2014

Drift issues of tall buildings during the March 11, 2011 M9.0 Tohoku earthquake, Japan - Implications

One of the most significant effects of the M9.0 Tohoku, Japan earthquake of March 11, 2011 is the now well-known long duration (>10 minutes) shaking of buildings in Japan – particularly those in Tokyo (~350-375 km from the epicenter) and in places as far as Osaka (~770 km from the epicenter). Although none collapsed, the strong shaking caused many tall buildings not to be functional for days and weeks. The purpose of this paper is to discuss the behavior and performance of four tall buildings, considered to be representative of most tall buildings in Tokyo and other locations, and from which shaking data were retrieved. Of particular interest is a building in Osaka that almost reached an average of 0.5% drift ratio – this, with a ground level input motion of ~3% g is significant. What might have happened during an event with input level motions with similar low frequency content and in 10-20% g range is a legitimate question that must be pondered. The particular building had serious site effects and was in resonance. The other three examples are from Tokyo. For example, based on records obtained from a 54-story building retrofitted with 288 oil dampers on 24 floors, computations show that average drift ratio may have reached ~0.3% and maximum drift ratio likely was > .3%. The maximum allowed by Japanese practice for buildings taller than 60 m and for collapse protection (level 2) motions is 1% (The Building Center of Japan, 2001). Performances of tall buildings in many seismically active regions of the world (e.g. Chile, Turkey) or those tall buildings affected by long distance long period effects by sources at a distance (e.g. Abu Dhabi, Dubai) are of interest to the earthquake engineering community. Chile imposes 0.2 % drift limit that result in elastic design. USA and Turkey impose 2% drift limit. Such wide variations of drift limits in design practices deserve discussion in light of functionality and performance of tall buildings during the 2011 Tohoku event.

Conference Paper↗
USGS2013

The effects of pulse pressure from seismic water gun technology on Northern Pike

We examined the efficacy of sound pressure pulses generated from a water gun for controlling invasive Northern Pike Esox lucius . Pulse pressures from two sizes of water guns were evaluated for their effects on individual fish placed at a predetermined random distance. Fish mortality from a 5,620.8-cm 3 water gun (peak pressure source level = 252 dB referenced to 1 μP at 1 m) was assessed every 24 h for 168 h, and damage (intact, hematoma, or rupture) to the gas bladder, kidney, and liver was recorded. The experiment was replicated with a 1,966.4-cm 3 water gun (peak pressure source level = 244 dB referenced to 1 μP at 1 m), but fish were euthanized immediately. The peak sound pressure level (SPL peak ), peak-to-peak sound pressure level (SPL p-p ), and frequency spectrums were recorded, and the cumulative sound exposure level (SEL cum ) was subsequently calculated. The SPL peak , SPL p-p , and SEL cum were correlated, and values varied significantly by treatment group for both guns. Mortality increased and organ damage was greater with decreasing distance to the water gun. Mortality (31%) by 168 h was only observed for Northern Pike exhibiting the highest degree of organ damage. Mortality at 72 h and 168 h postexposure was associated with increasing SEL cum above 195 dB. The minimum SEL cum calculated for gas bladder rupture was 199 dB recorded at 9 m from the 5,620.8-cm 3 water gun and 194 dB recorded at 6 m from the 1,966.4-cm 3 water gun. Among Northern Pike that were exposed to the large water gun, 100% of fish exposed at 3 and 6 m had ruptured gas bladders, and 86% exposed at 9 m had ruptured gas bladders. Among fish that were exposed to pulse pressures from the smaller water gun, 78% exhibited gas bladder rupture. Results from these initial controlled experiments underscore the potential of water guns as a tool for controlling Northern Pike.

Transactions of the American Fisheries Society↗
USGS1989

GEOS seismograms recorded for aftershocks of the earthquakes of December 7, 1988, near Spitak, Armenia SSR, during the time period 3 January 1989 through 2 February 1988 (UTC)

The earthquakes of December 7, 1988, near Spitak, Armenia SSR, serve as another grim reminder of the serious hazard that earthquakes pose throughout the world. We extend our heartfelt sympathies to the families of the earthquake victims and intend that our cooperative scientific endeavours will help reduce losses in future earthquakes. Only through a better understanding of earthquake hazards can earthquake losses be reduced for all peoples in seismically active regions of the world. The tragic consequences of these earthquakes remind scientists and public officials alike of their urgent responsibilities to understand and mitigate the effects of earthquakes. On behalf of the U.S. Geological Survey, I would like to express appreciation to our Soviet colleagues for their kind invitation to participate in joint scientific and engineering studies. Without their cooperation and generous assistance, the conduct of these studies would not have been possible. This report provides seismologic and geologic data collected during the time period December 21, 1988, through February 2, 1989. These data are presented in their entirety to expedite analysis of the data set for inferences regarding hazard mitigation actions, applicable not only in Armenia but other regions of the world exposed to high seismic risk

Open-File Report↗
USGS1996

Three-dimensional P and S wave velocity structure of Redoubt Volcano, Alaska

The three‐dimensional P and S wave structure of Redoubt Volcano, Alaska, and the underlying crust to depths of 7–8 km is determined from 6219 P wave and 4008 S wave first‐arrival times recorded by a 30‐station seismograph network deployed on and around the volcano. First‐arrival times are calculated using a finite‐difference technique, which allows for flexible parameterization of the slowness model and easy inclusion of topography and source‐receiver geometry. The three‐dimensional P wave velocity structure and hypocenters are determined simultaneously, while the three‐dimensional S wave velocity model is determined using the relocated seismicity and an initial S wave velocity model derived from the P wave velocity model assuming an average Vp / Vs ratio of 1.78. Convergence is steady with approximately 73% and 52% reduction in P and S wave arrival time RMS, respectively, after 10 iterations. The most prominent feature observed in the three‐dimensional velocity models derived for both P and S waves is a relative low‐velocity, near‐vertical, pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level. This feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit. The velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations. High velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates. No large low‐velocity body suggestive of a magma chamber is resolved in the upper 7–8 km of the crust.

Journal of Geophysical Research B: Solid Earth↗
USGS2022

P- and S-wave velocity estimation by ensemble Kalman inversion of dispersion data for strong motion stations in California

This study uses an ensemble Kalman method for near-surface seismic site characterization of 154 network earthquake monitoring stations in California to improve the resolution of S -wave velocity ( V S ) and P -wave velocity ( V P ) profiles—up to the resolution depth—coupled with better quantification of uncertainties compared to previous site characterization studies at this network. These stations were part of the Yong et al . site characterization project, with selected stations based on future recordings of ground motions that are expected to exceed 10 per cent peak ground acceleration in 50 yr. To estimate V S and V P from experimental dispersion data, Yong et al . investigated these stations using linearized (local search and iteration) routines, and Yong et al . later studied a subset of these stations using nonlinear (global search and optimization) routines. In both studies, the selection of model parameters—that is, discretization of the V S and V P profiles with only five fixed thickness layers—was mainly based on trial and error. In contrast, this paper uses an approximate Bayesian method to assimilate experimental dispersion data and sequentially update an ensemble of particle estimates that span the V S and V P parameter spaces. Doing so, we systematically determine the most probable profiles conditioned on the experimental dispersion data, the introduced noise levels, and a priori knowledge in the form of physical constraints. We consider two configurations to discretize the soil depth from the surface to half of the maximum discernible wavelength obtained from the experimental dispersion data, namely refined and coarse models, and two initial models for each configuration to study solution multiplicity. Our results suggest that using the refined model for the top surface layers improves the resolution of near-surface site characteristics and the model’s success rate in capturing dispersion data at high frequencies. All models result in similar V S but distinct V P profiles, with increasing uncertainty at deeper layers, suggesting that the fundamental mode of Rayleigh wave dispersion data is not adequate to constrain the P -wave velocity profile and the S -wave velocity close to the resolution depth.

California↗
USGS1973

Bottom features and processes related to drifting ice on the Arctic shelf, Alaska

Early investigations of artic shelf regions led to the hypothesis that certain micro-relief forms are related to the action of grounded ice (for example, Rex, 1955). Since the introduction of side-scan sonar as a tool for ocean-floor surveys, a number of workers have described the occurrence of linear bottom features produced by grounded ice. Such features have been found on modern polar shelves (Skinner, 1971; Pelletier and Shearer, 1972; Kovacs, 1972; Reimnitz and Barnes, 1972; Brooks, 1973), and as relict features (Berkson and Clay, 1973; Belderson and Wilson, 1973; Belderson and others, 1973). Studies of core samples, high resolution seismic profiles, and diving observations indicate that the sediments of the Beaufort Sea Shelf are highly distorted by the action of grounding ice, and that the recurrence rate of gouging is very high. It has also become evident that grounding ice is contributing considerably to the sediment transport processes of modern Arctic shelves. Sediments from similar environments exposed on the continents today should also contain the record of ice gouging and related processes. Thus it has become apparent that drifting ice is an important agent influencing the sedimentary structures and the sediment transport regime of Arctic shelves today and has been in the past. The diagrams presented here, with supporting evidence in the form of side-scan sonar records, and ice and bottom photos, demonstrate the most prevalent processes and types of bottom features observed on the continental shelf off northern Alaska. As the map shows, most of the shelf is affected by these processes today.

Alaska↗
USGS2013

Roman, Visigothic and Islamic evidence of earthquakes recorded in the archaeological site of “El Tolmo de Minateda” (Prebetic Zone, southeast of Spain)

The archaeological site of “El Tolmo de Minateda” is located within the Albacete province (SE of Spain) and shows a continuous time record of ancient civilizations from 3500 yr BP onwards. However, three temporal gaps were identified in this archaeological record, all of them in relationship with a sudden and unclear abandonment of the city (Centuries 1st, 7th and 9-10th). The Archaeological Earthquake Effects (EAEs) supports the possibility that moderate to strong earthquakes were the cause of such abandonments: oriented columns fallen, collapsed walls and arches, abandonment of irrigation systems and fresh-water supplies, crashed pottery, etc. Despite of the scarce of instrumental seismicity and a few historical chronicles, paleoseismic studies performed in the neighbouring zone (Tobarra) suggest the presence of closer seismic sources as faults (Pozohondo Fault) affecting Quaternary alluvial, lacustrine deposits and colluviums. In this work, we propose the possibility that three moderate earthquakes devastated the ancient Roman city of Ilunum (Century 1st AD), the Visigothic city of Elo (Century 7th AD) and the Islamic city of Madinat Iyih (Century 9th-10thAD), all of them the same place: “El Tolmo de Minateda”.

Cuaternario y Geomorfologia↗
USGS1993

Preventing volcanic catastrophe; the U.S. International Volcano Disaster Assistance Program

When the seismograph began to record the violent earth-shaking caused by yet another eruption of the Nevado del Ruiz volcano in Colombia, no one thought that a few hours later more than 23,000 people would be dead, killed by lahars (volcanic debris flows) in towns and villages several tens of kilometers away from the volcano. Before the fatal eruption the volcano was being monitored by scientists at a seismic station located 9 km from the summit, and information about the volcano's activity was being sent to Colombian emergency-response coordinators who were charged with alerting the public of the danger from the active volcano. Furthermore, area known to be in the pathways lahars had already been identified on maps and communities at risk had been told of their precarious locations. Unfortunately, a storm on November 13, 1985, obscured the glacier-clad summit of Nevado del Ruiz. On that night an explosive eruption tore through the summit and spewed approximately 20 million cubic meters of hot ash and rocks across the snow-covered glacier. These materials were transported across the snow pack by avalanches of hot volcanic debris (pyroclastic flows) and fast-moving, hot, turbulent clouds of gas and ash (pyroclastic surges). The hot pyroclastic flows and surges caused rapid melting of the snow and ice and created large volumes of water that swept down canyons leading away from the summit. As these floods of water descended the volcano, they picked up loose debris and soil from the canyon floors and walls, growing both in volume and density, to form hot lahars. In the river valleys farther down the volcano's flanks, the lahars were as much as 40 m thick and traveled at velocities as fast as 50 km/h. Two and a half hours after the start of the eruption one of the lahars reachered Armero, 74 km from the explosion crater. In a few short minutes most of the town was swept away or buried in a torrent of mud and boulders, and three quaters of the townspeople perished.

Nevado del Ruiz↗
USGS2019

Joint 3-D tomographic imaging of Vp, Vs and Vp/Vs and hypocenter relocation at Sinabung volcano, Indonesia from November to December 2013

We conducted travel time tomography using P- and S-wave arrival times of volcanic-tectonic (VT) events that occurred between November and December 2013 to determine the three-dimensional (3D) seismic velocity structure (Vp, Vs, and Vp/Vs) beneath Sinabung volcano, Indonesia in order to delineate geological subsurface structure and to enhance our understanding of the volcanism itself. This was a time period when phreatic explosions became phreatomagmatic and then magma migrated to the surface forming a summit lava dome. We used 4846 VT events with 16,138 P- and 16,138 S-wave arrival time phases recorded by 6 stations for the tomographic inversion. The relocated VTs collapse into three clusters at depths from the surface to sea level, from 2 to 4 km below sea level, and from 5 to 8.5 km below sea level. The tomographic inversion results show three prominent regions of high Vp/Vs (~ 1.8) beneath Sinabung volcano at depths consistent with the relocated earthquake clusters. We interpret these anomalies as intrusives associated with previous eruptions and possibly surrounding the magma conduit, which we cannot resolve with this study. One anomalous region might contain partial melt, at sea level and below the eventual eruption site at the summit. Our results are important for the interpretation of a conceptual model of the “plumbing system” of this hazardous volcano.

Sinabung Volcano↗