Temporal Distribution Of Events Research Articles

Low-magnitude seismic swarms in the Calabrian Arc (Italy)

AbstractSeismic swarms of low magnitude earthquakes occur frequently in the Calabrian Arc. During the last few years, several earthquakes of magnitude up to ML4.4 occurred both on land and offshore near the coast of Calabria. Some of them were followed by a sequence of tens to hundreds of smaller, well-clustered earthquakes that occurred during the following weeks or months. In other cases, swarms of low-magnitude earthquakes occur without a classical mainshock-aftershock evolution. In this work, we selected swarms that were well recorded by a high number of seismic stations to perform a detailed analysis consisting of the determination of the relative location and focal mechanism for as many earthquakes as possible. In some cases, the relative location allows to recognize the seismogenic fault and to distinguish the fault plane from the auxiliary plane of the focal mechanism solution. In other cases, the relative location unravels a small cloud of events that is not compatible with a unique fault plane, suggesting the occurrence of the swarm in highly fractured seismogenic volume. The relative hypocenter positions allow to estimate the size of the seismogenic volume, which is very small in most of the cases, often less than 1 km3. However, its extension is greater than the size computed for the mainshock rupture in many cases. The most common source mechanism is of normal type, but strike-slip and reverse kinematics are also found, in particular for swarms located offshore and near the coast. The temporal distribution of events does not show any evident migration of the sources, thus suggesting that the driving mechanism is not related with aseismic phenomena like fluid diffusion and stress waves.

A Pilot Study of Detecting Individual Sleep Apnea Events Using Noncontact Radar Technology, Pulse Oximetry, and Machine Learning

The gold standard for assessing sleep apnea, polysomnography, is resource intensive and inconvenient. Thus, several simpler alternatives have been proposed. However, validations of these alternatives have focused primarily on estimating the apnea‐hypopnea index (apnea events per hour of sleep), which means information, clearly important from a physiological point of view such as apnea type, apnea duration, and temporal distribution of events, is lost. The purpose of the present study was to investigate if this information could also be provided with the combination of radar technology and pulse oximetry by classifying sleep apnea events on a second‐by‐second basis. Fourteen patients referred to home sleep apnea testing by their medical doctor were enrolled in the study (6 controls and 8 patients with sleep apnea; 4 mild, 2 moderate, and 2 severe) and monitored by Somnofy (radar‐based sleep monitor) in parallel with respiratory polygraphy. A neural network was trained on data from Somnofy and pulse oximetry against the polygraphy scorings using leave‐one‐subject‐out cross‐validation. Cohen’s kappa for second‐by‐second classifications of no event/event was 0.81, or almost perfect agreement. For classifying no event/hypopnea/apnea and no event/hypopnea/obstructive apnea/central apnea/mixed apnea, Cohen’s kappa was 0.43 (moderate agreement) and 0.36 (fair agreement), respectively. The Bland‐Altman 95% limits of agreement for the respiratory event index (apnea events per hour of recording) were ‐8.25 and 7.47, and all participants were correctly classified in terms of sleep apnea severity. Furthermore, the results showed that the combination of radar and pulse oximetry could be more accurate than the two technologies separately. Overall, the results indicate that radar technology and pulse oximetry could reliably provide information on a second‐by‐second basis for no event/event which could be valuable for management of sleep apnea. To be clinically useful, a larger study is necessary to validate the algorithm on a general population.

Evolution of events before and after the 17 June 2017 rock avalanche at Karrat Fjord, West Greenland – a multidisciplinary approach to detecting and locating unstable rock slopes in a remote Arctic area

Abstract. The 17 June 2017 rock avalanche in the Karrat Fjord, West Greenland, caused a tsunami that flooded the nearby village of Nuugaatsiaq and killed four people. The disaster was entirely unexpected since no previous records of large rock slope failures were known in the region, and it highlighted the need for better knowledge of potentially hazardous rock slopes in remote Arctic regions. The aim of the paper is to explore our ability to detect and locate unstable rock slopes in remote Arctic regions with difficult access. We test this by examining the case of the 17 June 2017 Karrat rock avalanche. The workflow we apply is based on a multidisciplinary analysis of freely available data comprising seismological records, Sentinel-1 spaceborne synthetic-aperture radar (SAR) data, and Landsat and Sentinel-2 optical satellite imagery, ground-truthed with limited fieldwork. Using this workflow enables us to reconstruct a timeline of rock slope failures on the coastal slope here collectively termed the Karrat Landslide Complex. Our analyses show that at least three recent rock avalanches occurred in the Karrat Landslide Complex: Karrat 2009, Karrat 2016, and Karrat 2017. The latter is the source of the abovementioned tsunami, whereas the first two are described here in detail for the first time. All three are interpreted as having initiated as dip-slope failures. In addition to the recent rock avalanches, older rock avalanche deposits are observed, demonstrating older (Holocene) periods of activity. Furthermore, three larger unstable rock slopes that may pose a future hazard are described. A number of non-tectonic seismic events confined to the area are interpreted as recording rock slope failures. The structural setting of the Karrat Landslide Complex, namely dip slope, is probably the main conditioning factor for the past and present activity, and, based on the temporal distribution of events in the area, we speculate that the possible trigger for rock slope failures is permafrost degradation caused by climate warming. The results of the present work highlight the benefits of a multidisciplinary approach, based on freely available data, to studying unstable rock slopes in remote Arctic areas under difficult logistical field conditions and demonstrate the importance of identifying minor precursor events to identify areas of future hazard.

Mining Activities and the Spatial-Temporal Variations of Earthquakes in Southern Africa

Spatial-temporal variations in earthquake occurrence have been studied in many regions of the world but little can be said aboutthe Southern Africa Region in this regard. Using earthquakes of magnitudes greater than or equal to one together with theFORTRAN language and Generic Mapping Tools (GMT), spatial variations of earthquakes spanning the period 1966 to 2014were examined for the region. Similarly, the temporal variations with earthquakes of magnitudes greater than or equal to fourwere studied. The spatial analysis showed that the highest number of events (1438) in the period occurred at an average depthof around 7.5 km representing approximately 79.9 % of the total earthquakes considered. The temporal distribution of events onthe other hand showed that the highest number of events (590) were recorded in the year 1993. Three main issues were identifiedas potential factors responsible for the observed variations. Activities such as mining and failures in weak zones of the rockmass as well as increase in the number of stations were identified as the key factors responsible for the observed distributions.The third factor could not be independently verified. However, earlier studies suggest that this factor indeed have caused majorearthquakes in the region.

Site-specific uniform hazard spectrum in Eastern Turkey based on simulated ground motions including near-field directivity and detailed site effects

In this study, stochastic earthquake catalog of the Erzincan region in Turkey is generated based on synthetic ground motions. Monte Carlo simulation method is used to identify the spatial and temporal distribution of events. Ground motion time histories are generated using stochastic simulation methodology. Annual exceedance rate of each ground motion amplitude is calculated through statistical distribution of the complete set of ground motions. The results are compared with classical probabilistic seismic hazard analysis (PSHA). Classical PSHA generally produces larger spectral amplitudes than the proposed study due to wide range of aleatory variability. The effects of near-field forward directivity and detailed site response are also investigated on the results.

Disaster risk profiling in southern Africa: inventories, impacts and implications

Enhanced ways to cope with climate change and environmental change are being made at various levels across the world. In the southern African region, despite the regions’ potential for economic growth, several disasters associated with climate stresses (particularly evidence made for repeated floods and droughts) can retard economic growth, development and livelihood security. In this paper, disaster inventories are argued to be useful ways of revealing nuanced analyses of extreme climate events and other challenges such as the spatial–temporal distribution of events and their impacts, particularly for vulnerable people groups. Despite repeated calls for vigilance about current and future climate variations and environmental change impacts, there are few detailed regional and country-specific inventories of disasters and records of subsequent humanitarian responses that record both impacts and possible implications of disaster events in the region. This paper draws together those data that do exist and offers a review of the occurrences, impacts and past responses to humanitarian crises in the region (for 14 countries over the period of 2000–2012). From this research a number of critical areas are profiled: first, the convergence of compound and complex shocks that occur simultaneously and/or sequentially is compounding disaster risks—including those associated with climate challenges. A review of international and regional UN agency, NGO and governmental reports all illustrates the need to articulate between internationally significant, ‘signature’ events and smaller, sub-national events with a higher recurrence interval that may be just as damaging to local communities. Second, the reach of disaster impacts is changing with the region becoming increasingly more mobile in terms of the movement patterns of people within countries and across borders, which brings with it new compound and complex threats such as cholera and measles outbreaks. Third, the nature of the changing disaster profile is placing strain on countries and the region. Sub-national disaster response due to personnel capacity limitations, at the national and municipal levels, is unable to effectively respond to and reduce risks associated with various shocks. In the paper, by providing an inventory of disasters and humanitarian responses in the southern African region, we point to the changing regional and national dimensions of the region’s disaster risk profile that, we suggest, will require a variety of responses.

The causes and mechanisms of moraine-dammed lake failures in the Cordillera Blanca, North American Cordillera, and Himalayas

Glacial lake outburst floods (GLOFs) from moraine-dammed lake failures represent a significant threat to inhabitants of high mountain areas across the globe. The first part of this paper summarises the causes and mechanisms of moraine-dammed lake failures through a review of the scientific literature and unpublished reports. There are eight main causes, of which five are characterised as dynamic and three as long-term, and these are associated with around twenty failure mechanisms. The dynamic causes are slope movements into the lake, earthquakes, flood waves from a lake situated upstream, blocking of underground outflow channels, and intensive rainfall or snowmelt. The long-term causes are the melting of buried ice, the impact of hydrostatic pressure, and the effect of time. These causes (triggers) and the consequent mechanisms of dam failure are described in detail. The second part compares the historical moraine-dammed lake failures within three regions between 1900 and 2009: the Cordillera Blanca of Peru, the North American Cordillera, and the Himalayas. It has been found that dynamic causes are around four times more common than long-term causes although significant regional differences have beenobserved. The most frequent causes in these regions were found to be slope movements in which the displaced material was dominated by solid-state water (ice falls, ice avalanches, and snow avalanches). The other causes tended to show distinct regional patterns while the temporal distribution of events also differs according to region. In the North American Cordillera and Himalayas moraine dam failures occur exclusively during the summer season while in the Cordillera Blanca they are more evenly distributed with the exception of the dry season. This reflects the general climatic setting of each of the study regions.

Seasonal and Weekly Patterns of Occurrence of Acute Cardiovascular Diseases: Does a Gender Difference Exist?

Cardiovascular (CV) disease is the leading cause of death in women. It is known that acute CV events exhibit temporal patterns of onset, that is, seasonal and weekly. We aimed to verify whether such patterns show differences by gender. We analyzed cumulative data from our previous studies dealing with hospital admissions for CV events, such as acute myocardial infarction (AMI), stroke, transient ischemic attack (TIA), aortic diseases (AD), and pulmonary embolism (PE), in the region Emilia-Romagna (RER) of Italy (ICDM9-CM codes, years 1998?2006). Total population and subgroups by gender (percentage of monthly and daily events) were tested for uniformity with the chi-square test, and a chronobiologic method was applied to monthly percentage of data for seasonal rhythmic analysis. Season: We considered 130,693 patients (45.1% women): 64,191 AMI, 43,642 TIA, 4,615 AD, 19,425 PE. The monthly and seasonal distribution showed respective peaks in January and in winter, with no differences by gender. Day-of-week: We considered 168,921 patients (45.6% women): 64,191 AMI, 56,453 stroke, 43,642 TIA, 4,615 AD. The weekly distribution showed a peak on Monday, with no differences by gender. A multivariate regression logistic analysis, including in the model either major CV risk factors (hypertension, dyslipidemia, diabetes mellitus) and subgroups by age, did not find any difference in the temporal distribution of events in women and men. The seasonal and day-of-week distribution of occurrence of CV events seems to be independent of gender.

Temporal feature of BOLD responses varies with temporal patterns of movement

Which brain sites represent the final form of motor commands that encode temporal patterns of muscle activities? Here, we show the possible brain sites which have activity equivalent to the motor commands with functional magnetic resonance imaging (fMRI). We hypothesized that short-temporal patterns of movements or stimuli are reflected in blood-oxygenation-level-dependent (BOLD) responses and we searched for regions representing the response. Participants performed two temporal patterns of tapping and/or listened to the same patterns of auditory stimuli in a 3T fMRI. The patterns were designed to have the same number (11) of events and the same duration, but different temporal distribution of events. The 11 events were divided into two parts (10 repetitive taps and one stand-alone tap) and the interval of the two parts was 3 s. The two patterns had reverse order of the two parts. The results revealed that different temporal patterns of auditory stimuli were represented in different temporal features of BOLD responses in the bilateral auditory cortex, whereas different temporal patterns of tapping were reflected in contralateral primary motor cortex and the ipsilateral anterior cerebellum. In bilateral premotor cortex, supplementary motor area, visual cortex, and posterior cerebellum, task-related BOLD responses were exhibited, but their responses did not reflect the temporal patterns of the movement and/or stimuli. One possible explanation is that the neuronal activities were similar for the two patterns in these regions. The sensitivity of the BOLD response to the temporal patterns reflects local differences in functional contributions to the tasks. The present experimental design and analysis may be useful to reveal particular brain regions that participate in multiple functions.

Analysis of glacial earthquakes

In 2003, Ekström et al. reported on the detection of a new class of earthquakes that occur in glaciated regions, with the vast majority being in Greenland. The events have a characteristic radiation pattern and lack the high‐frequency content typical of tectonic earthquakes. It was proposed that the events correspond to large and sudden sliding motion of glaciers. Here we present an analysis of all 184 such events detected in Greenland between 1993 and 2005. Fitting the teleseismic long‐period surface waves to a landslide model of the source, we obtain improved locations, timing, force amplitudes, and force directions. After relocation, the events cluster into seven regions, all of which correspond to regions of very high ice flow and most of which are named outlet glaciers. These regions are Daugaard Jensen Glacier, Kangerdlugssuaq Glacier, Helheim Glacier, the southeast Greenland glaciers, the northwest Greenland glaciers, Rinks Isbrae, and Jakobshavn Isbrae. Event amplitudes range from 0.1 to 2.0 × 1014kg m. Force directions are consistent with sliding in the direction of glacial flow over a period of about 50 s. Each region has a different temporal distribution of events. All glaciers are more productive in the summer, but have their peak activity in different months. Over the study period, Kangerdlugssuaq has had a constant number of events each year, whereas Jakobshavn had most events in 1998–1999, and the number of events in Helheim and the northwest Greenland glaciers has increased substantially between 1993 and 2005. The size distribution of events in Kangerdlugssuaq is peaked above the detection threshold, suggesting that glacial earthquakes have a characteristic size.

Multifractal and Chaotic Analysis of Vrancea (Romania) Intermediate-depth Earthquakes: Investigation of the Temporal Distribution of Events

The Vrancea seismic region contains an isolated cluster of events beneath the Carpathian Arc Bend in Romania, dipping to about 200 km depth. Seismic activity mainly occurs at intermediate depths (h > 60 km). The main goal of the paper is to perform an in-depth, complex analysis of the occurrence times of these intermediate-depth events. We also try to show the versatility of the methods used to characterize different aspects of the seismicity evolution and to offer a user-friendly software toolbox to do most of the related computations. The earthquake catalog used in this study spans from 1974 to 2002 and includes only the intermediate-depth events. In the first part of the paper, we analyze the multifractal characteristics of the temporal distribution of earthquakes. The study reveals two distinct scaling regimes. At small scales we found a clear nonhomogeneous, multifractal pattern, while at large scales the temporal distribution of events shows a monofractal, and close to Poissonian (random), behavior. The multifractal behavior at small scales (minutes-hours) is shown to be clearly an effect of the “short” aftershock sequences that occurred after some major Vrancea earthquakes. In the second part of the paper we analyze whether our temporal series shows a persistent (or anti-persistent) long-term behavior, by using the Detrended Fluctuation Analysis (DFA) method. The results suggest that the analyzed temporal series of Vrancea earthquakes is a non-correlated process. In part three of the paper we seek to determine whether the dynamics of our earthquake system (described by the occurrence time of Vrancea earthquakes) is deterministically chaotic, deriving from a rather simple evolution law, or whether it is stochastic and is generated by a system that possesses many degrees of freedom. The results suggest that our signal is stochastic (probably does not possess an attractor). The limited time-span of the catalog and the analysis performed in this paper cannot rule out the emergence of an interesting, quasi-deterministic and low-dimensional structure in the case of major Vrancea earthquakes.

Fractal analysis of earthquake swarms of Vogtland/NW-Bohemia intraplate seismicity

The special type of intraplate microseismicity with swarm-like occurrence of earthquakes within the Vogtland/NW-Bohemian Region is analysed to reveal the nature and the origin of the seismogenic regime. The long-term data set of continuous seismic monitoring since 1962, including more than 26000 events within a range of about 5 units of local magnitude, provides an unique database for statistical investigations. Most earthquakes occur in narrow hypocentral volumes (clusters) within the lower part of the upper crust, but also single event occurrence outside of spatial clusters is observed. Temporal distribution of events is concentrated in clusters (swarms), which last some days until few month in dependence of intensity. Since 1962 three strong swarms occurred (1962, 1985/86, 2000), including two seismic cycles. Spatial clusters are distributed along a fault system of regional extension (Leipzig-Regensburger Störung), which is supposed to act as the joint tectonic fracture zone for the whole seismogenic region. Seismicity is analysed by fractal analysis, suggesting a unifractal behaviour of seismicity and uniform character of seismotectonic regime for the whole region. A tendency of decreasing fractal dimension values is observed for temporal distribution of earthquakes, indicating an increasing degree of temporal clustering from swarm to swarm. Following the idea of earthquake triggering by magma intrusions and related fluid and gas release into the tectonically pre-stressed parts of the crust, a steady increased intensity of intrusion and/or fluid and gas release might account for that observation. Additionally, seismic parameters for Vogtland/NW-Bohemia intraplate seismicity are compared with an adequate data set of mining-induced seismicity in a nearby mine of Lubin/Poland and with synthetic data sets to evaluate parameter estimation. Due to different seismogenic regime of tectonic and induced seismicity, significant differences between b-values and temporal dimension values are observed. Most significant for intraplate seismicity are relatively low fractal dimension values for temporal distribution. That observation reflects the strong degree of temporal earthquake clustering, which might explain the episodic character of earthquake swarms and support the idea of push-like triggering of earthquake avalanches by intruding magma.

The earthquake swarm 2000 in the region Vogtland/NW-Bohemia—earthquake recording at German stations and temporal distribution of events

The last strong earthquake swarm in the region Vogtland/NW-Bohemia occurred between August and November 2000 with about 10000 micro-earthquakes at magnitudes up to 3.7. On the territory of Germany the seismic activity was monitored both by means of permanent and mobile stations. Mobile stations were installed by the Seismological Central Observatory at Erlangen (SZGRF) in co-operation with the “Geo-Forschungs-Zentrum”-(GFZ)-Potsdam and the University of Potsdam. The objects of this paper are: (1) the presentation of seismic stations on the German side of the earthquake region during the swarm 2000, (2) the comparison of the frequency–time and magnitude–time distribution of the recent swarm 2000 with previous swarms in the 20th century.

Is life stress more likely to provoke depressive episodes in women than in men?

One of the most consistent findings in psychiatric research is that rates of major depression are at least twofold higher among women than among men. Although there is considerable agreement in the literature that life events play a role in producing, triggering, or maintaining episodes of depression, less is known about the relationship among gender, life events, and depression. In the present study, we compared the rates, focus ("interpersonal" vs. "non-interpersonal"), and timing of stressful life experiences reported in rigorous interviews of male and female patients with unipolar recurrent depression and nondepressed contrast subjects. Consistent with hypotheses, female patients were more likely to experience stressful life experiences than their male counterparts; rates of stressful life experiences did not differ between female and male controls. Unexpectedly, rates of interpersonal stress did not differ among males and females regardless of patient or control status. We also found no significant differences in the timing of pre-onset events: stressful events were generally concentrated in the period immediately preceding onset for both men and women. Thus, although these data suggest that life stress may play a larger role in the provocation of recurrent episodes of depression for women than for men, there do not seem to be sex differences in the extent to which interpersonal vs. noninterpersonal events and difficulties are associated with depression onset or in the temporal distribution of events. Implications of these results are discussed in the context of research on other putative factors contributing to gender differences in rates of depression.

Moment spectra in a simple model of an earthquake fault

The behavior of a simple one‐dimensional, homogeneous, deterministic model of an earthquake fault is examined on the timescale of the rupture process. The model generates a complex spatial and temporal distribution of events from a frictional instability. I measure the frequency spectra of the moment release rate for events of different sizes, and observe power laws for the spectra. A bend in the spectra of large events is also observed. The paper concludes with a discussion of how these results may be relevant to real earthquake faults.