scholarly journals An instrumental earthquake catalogue for the offshore Maltese islands region, 1995–2014

2020 ◽  
Vol 63 (Vol 63 (2020)) ◽  
Author(s):  
Matthew Agius ◽  
Pauline Galea ◽  
Daniela Farrugia ◽  
Sebastiano D'Amico
Keyword(s):  
Seismic Data ◽  
Earthquake Catalogue ◽  
Data Recording ◽  
High Concentration ◽  
Regional Networks ◽  
Regional Seismicity ◽  
Maltese Islands ◽  
Single Station ◽  
Sicily Channel ◽  
Formed Part

We present the first earthquake catalogue for Malta using 20 years of broadband seismic data recording. For about two decades Malta had only one station (WDD) which formed part of regional networks. Its location in the eastern part of the Sicily Channel puts the station at the periphery of these networks with the result that weak, off-shore earthquakes that occur between Malta and Libya, are in many cases recorded on WDD only and are undetected or unlisted by the regional networks. We adopt the single-station earthquake location method to process the continuously recorded seismic data of station WDD from 1995 to 2014. We combine our earthquake list with the bulletins of INGV and IRIS to catalogue 550 earthquakes. We statistically quantify the uncertainties of the earthquake epicentres and establish that many earthquake locations differ from INGV/IRIS locations by < 20 km at local epicentral distances from WDD and that earthquake magnitudes determined from single-station are overestimated by 0.2. We find that the Malta and Linosa grabens are seismically active, and a high concentration of seismic activity is located 80–120 km SSE of Malta at around 35◦N latitude. Closer to land, clusters of epicentres are also located, within 40 km to the east and south of Malta. This new earthquake catalogue shows that the regional seismicity is higher than previously observed and that a number of submarine structures in the area are active as part of the ongoing extension in the Sicily Channel.

Seismic data recording — The limiting component

1990 ◽  
Author(s):  
A. D. Beecroft ◽  
Albert Stienstra ◽  
A. S. Badger
Keyword(s):  
Seismic Data ◽  
Data Recording

The national seismic network for the Maltese islands: Update 2021

2021 ◽  
Author(s):  
Pauline Galea ◽  
Matthew Agius ◽  
George Bozionelos ◽  
Sebastiano D'Amico ◽  
Daniela Farrugia
Keyword(s):  
Real Time ◽  
Site Response ◽  
Seismic Monitoring ◽  
Seismic Network ◽  
Local Network ◽  
Time Data ◽  
African Plate ◽  
Seismic Stations ◽  
Maltese Islands ◽  
Sicily Channel

&lt;p&gt;The Maltese islands are a small country 15 km wide by 30 km long located about 100 km south of Sicily, Italy. Since 2015 Malta has set up a national seismic network. The primary aim of this network is to monitor in real-time and to locate more accurately the seismicity close to the islands and the seismicity in the Sicily Channel, offshore between Sicily, Tunisia and Libya. This Channel presents a range of interesting and complex tectonic processes that have developed in response to various regional stress fields mainly as a result of the collision between the African plate with Europe. The Maltese islands are known to have been affected by a number of earthquakes originating in the Channel, with some of these events estimated to be very close to the islands.&lt;/p&gt;&lt;p&gt;The seismotectonic characteristics of the Sicily channel, particularly south of the Maltese islands, is not well understood. This situation is being partially addressed through an increase in the number of seismic stations on the Maltese archipelago. The Malta Seismic Network (FDSN code ML), managed by the Seismic Monitoring and Research Group, within the Department of Geosciences, University of Malta, currently comprises 8 broadband, 3-component stations over an area slightly exceeding 300 km&lt;sup&gt;2&lt;/sup&gt;. We present a technical description of the MSN including quality control tests such as spectral analysis (Power Spectral Density and HVSR), station orientations and timings as well as examples of local and regional earthquakes recorded on the network. We describe the upgrades to real-time data transmission and archiving, and automated epicentre location for continuous seismic monitoring using the local network amalgamated with a virtual seismic network to monitor the seismicity in the extended Mediterranean region. Such a dense national network, besides improving epicentral location in the Sicily Channel, is providing valuable information on microearthquake activity known to occur in close proximity to the islands, which has been very difficult to study in the past. It also provides an important tool for analysing site response and site amplification related to underlying geology, which constitutes a major component of seismic hazard analysis on the islands. Furthermore, the increase in seismic stations to the seismic monitoring system provides more robust earthquake estimates for the tsunami monitoring/simulation system.&lt;/p&gt;&lt;p&gt;Funding for stations was provided by Interreg Italia-Malta projects (SIMIT and SIMIT-THARSY, Codes B1-2.19/11 and C1-3.2-57) and by Transport Malta.&lt;/p&gt;

Hierarchical exploration of single station seismic data with unsupervised learning

2021 ◽  
Author(s):  
René Steinmann ◽  
Leonard Seydoux ◽  
Michel Campillo
Keyword(s):  
Unsupervised Learning ◽  
Seismic Data ◽  
Acoustic Emissions ◽  
Agglomerative Clustering ◽  
Data Set ◽  
Seismic Waveforms ◽  
The North ◽  
Signal Features ◽  
Single Station ◽  
Seismic Crisis

&lt;p&gt;Seismic datasets contain an enormous amount of information and a large variety of signals with different origins. We usually observe signatures of earthquakes, volcanic and non-volcanic tremors, rockfalls, road and air traffic, atmospheric perturbations and many other acoustic emissions. More and more seismic sensors are deployed worldwide and record the seismic wavefield in a continuous fashion, generating massive volumes of data that cannot be analyzed manually in decent times. Therefore, identifying classes of signals in seismic data with automatic strategies is a crucial stage towards the understanding of the underlying physics of geological objects. For that reason seismologists have developed different tools to detect and classify certain types of signals. Recently, machine learning gained much attention due to its ability to recognize patterns. While supervised learning is a great tool for detecting and classifying signals within already-known classes, it cannot be used to infer new classes of signals, and can be strongly biased by the labels we impose. We here propose to overcome this limitation with unsupervised learning. In this study, we present a new way to explore single-station continuous seismic data with a dendrogram produced by agglomerative clustering. Our method is motivated by the idea that labels in a seismic data set follow a hierarchical order with different levels of details. For example earthquakes belong to the larger class of stationary signals and can be also divided into subclasses with different focal mechanism or magnitudes. We first use a scattering network (a convolutional neural network that makes use of wavelet filers) in order to extract a multi-scale representation of the continuous seismic waveforms. We then select the most meaningful features by means of independent component analysis, and apply an agglomerative clustering on this representation. We finally explore the dendrogram in a systematic way in order to explore the different signal classes revealed by the strategy. We illustrate our method on seismic data continuously recorded in the vicinity of the North-Anatolian fault, in Turkey. During this time period, a seismic crisis with more than 200 micro-earthquakes occurred, together with many other anthropogenic and meteorological events. By exploring the classes revealed by the dendrogram with &lt;em&gt;a posteriori&lt;/em&gt; signal features (occurrence, within-class correlations, etc.) we show that the strategy is capable of retrieving the seismic crisis as well as signals related to anthropogenic and meteorogical activities.&lt;/p&gt;

Lateral accretion in a straight slope channel system: an example from the Forties Sandstone of the Huntington Field, UK Central North Sea

2017 ◽  
Vol 8 (1) ◽  
pp. 413-428 ◽  
Author(s):  
Chris Edwards ◽  
Sean McQuaid ◽  
Stewart Easton ◽  
Don Scott ◽  
Andrew Couch ◽  
...  
Keyword(s):  
North Sea ◽  
Seismic Data ◽  
High Concentration ◽  
Channel Networks ◽  
Channel System ◽  
Flow Circulation ◽  
Meander Bends ◽  
The Right ◽  
Central North Sea ◽  
Slope Channel

AbstractA rich dataset of core, well logs and 3D seismic data has been integrated to establish a depositional hierarchy of a Paleocene-aged, Forties slope channel system of the Huntington Field, Block 22/14b of the Central North Sea. The reservoir consists of a mix of high-concentration turbidites and muddy and sandy debrites deposited as a series of laterally offset, slope channel fills. Seismic data reveal that the channels were remarkably straight and devoid of meander bends, more commonly associated with sinuous slope channel networks. Paradoxically, the internal offlapping architecture draws close comparisons with lateral accretion packages that are widely accepted to be the products of secondary flow circulation around sinuous channel bends. The straight nature of the Huntington channels precludes such an interpretation but can be explained as a consequence of Coriolis effects acting upon suspension-dominated flows in Northern Hemisphere high latitudes, resulting in the preferential accretion of sediment along the right-hand bank (when viewed downstream) and leading to the eventual lateral avulsion of the channel. The observed architecture has been incorporated into a reservoir model in order to characterize the static connectivity of the field that will in turn serve as a basis for understanding production behaviour.

scholarly journals A simple method to evaluate the air-to-ground coupling efficiency: a tool helping the assessment of seismic/infrasonic energy partitioning during an eruption

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Mie Ichihara ◽  
Kazuya Yamakawa ◽  
Dan Muramatsu
Keyword(s):  
Response Function ◽  
Seismic Data ◽  
Seismic Waves ◽  
Seismic Station ◽  
Coupling Efficiency ◽  
Data Set ◽  
Simple Method ◽  
Ground Shaking ◽  
Acoustic Data ◽  
Single Station

AbstractA volcanic eruption transmits both seismic and infrasound signals. The seismo-acoustic power ratio is widely used to investigate the eruption behaviors and the source dynamics. It is often the case that seismic data during an eruption are significantly contaminated or even dominated by ground shaking due to infrasound (air-to-ground signals). To evaluate the contribution of infrasound-originated power in the seismic data, we need a response function of the seismic station to infrasound. It is rare to obtain a seismo-acoustic data set containing only infrasound signals, though it is ideal for calculating the response function. This study proposes a simple way to calculate the response function using seismo-acoustic data containing infrasound and independent seismic waves. The method requires data recorded at a single station and mainly uses the cross-correlation function between the infrasound data and the Hilbert transform of the seismic data. It is tested with data recorded by a station at Kirishima volcano, Japan, of which response function has been constrained. It is shown that the method calculates a proper response function even when the seismic data contain more significant seismic power (or noise) than the air-to-ground signals. The proposed method will be useful in monitoring and understanding eruption behaviors using seismo-acoustic observations.

Methods of correlation noise minimization and suppression for multisource acquisition in vibroseis survey

2019 ◽  
pp. 98-106
Author(s):  
A. N. Oshkin ◽  
A. I. Kon’kov ◽  
A. V. Tarasov ◽  
A. A. Shuvalov ◽  
V. I. Ignat’ev
Keyword(s):  
Seismic Data ◽  
Synthetic Data ◽  
Seismic Source ◽  
Recording System ◽  
Signal Separation ◽  
Median Filtering ◽  
Data Recording ◽  
Single Source ◽  
Correlation Noise ◽  
Incoherent Noise

The use of several simultaneously operating sources in seismic operations allows one to obtain large amounts of data per unit of time than for classical works with a single source, and also to improve the seismic data recording system. Depending on the type of seismic source used (vibrating or pulsed), different methods of signal separation are used. When working with vibroseismic method, separation of signals becomes possible at the stage of correlative processing of vibrograms. In this paper, we demonstrate methods for constructing noncorrelating signals for use in vibroseis survey (with an example of using such signals on synthetic data) and hyperbolic median filtering to minimize correlation and incoherent noise.

Sediments with gas hydrates: Internal structure from seismic AVO

Geophysics ◽  
1998 ◽  
Vol 63 (5) ◽  
pp. 1659-1669 ◽  
Author(s):  
Christine Ecker ◽  
Jack Dvorkin ◽  
Amos Nur
Keyword(s):  
Internal Structure ◽  
Wave Velocity ◽  
Seismic Data ◽  
Pore Space ◽  
Rock Physics ◽  
P Wave ◽  
S Wave ◽  
High Concentration ◽  
Amplitude Variation With Offset ◽  
Bottom Simulating Reflector

We interpret amplitude variation with offset (AVO) data from a bottom simulating reflector (BSR) offshore Florida by using rock‐physics‐based synthetic seismic models. A previously conducted velocity and AVO analysis of the in‐situ seismic data showed that the BSR separates hydrate‐bearing sediments from sediments containing free methane. The amplitude at the BSR are increasingly negative with increasing offset. This behavior was explained by P-wave velocity above the BSR being larger than that below the BSR, and S-wave velocity above the BSR being smaller than that below the BSR. We use these AVO and velocity results to infer the internal structure of the hydrated sediment. To do so, we examine two micromechanical models that correspond to the two extreme cases of hydrate deposition in the pore space: (1) the hydrate cements grain contacts and strongly reinforces the sediment, and (2) the hydrate is located away from grain contacts and does not affect the stiffness of the sediment frame. Only the second model can qualitatively reproduce the observed AVO response. Thus inferred internal structure of the hydrate‐bearing sediment means that (1) the sediment above the BSR is uncemented and, thereby, mechanically weak, and (2) its permeability is very low because the hydrate clogs large pore‐space conduits. The latter explains why free gas is trapped underneath the BSR. The seismic data also indicate the absence of strong reflections at the top of the hydrate layer. This fact suggests that the high concentration of hydrates in the sediment just above the BSR gradually decreases with decreasing depth. This effect is consistent with the fact that the low‐permeability hydrated sediments above the BSR prevent free methane from migrating upwards.

scholarly journals A multi-centennial record of past floods and earthquakes in Valle d'Aosta, Mediterranean Italian Alps

2017 ◽  
Vol 17 (5) ◽  
pp. 613-625 ◽  
Author(s):  
Bruno Wilhelm ◽  
Hendrik Vogel ◽  
Flavio S. Anselmetti
Keyword(s):  
Lake Sediment ◽  
Seismic Data ◽  
Decadal Variability ◽  
Italian Alps ◽  
Regional Seismicity ◽  
The Past ◽  
Event Layers ◽  
Regional Earthquake ◽  
Precipitation Events

Abstract. Mediterranean Alpine populations are particularly exposed to natural hazards like floods and earthquakes because of both the close Mediterranean humidity source and the seismically active Alpine region. Knowledge of long-term variability in flood and earthquake occurrences is of high value since it can be useful to improve risk assessment and mitigation. In this context, we explore the potential of a lake-sediment sequence from Lago Inferiore de Laures in Valle d'Aosta (Northern Italy) as a long-term record of past floods and earthquakes. The high-resolution sedimentological study revealed 76 event layers over the last ca. 270 years; 8 are interpreted as most probably induced by earthquakes and 68 by flood events. Comparison to historical seismic data suggests that the recorded earthquakes are strong (epicentral Medvedev–Sponheuer–Kárník (MSK) intensity of VI–IX) and/or close to the lake (distance of 25–120 km). Compared to other lake-sediment sequences, Lago Inferiore de Laures sediments appear to be regionally the most sensitive to earthquake shaking, offering a great potential to reconstruct the past regional seismicity further back in time. Comparison to historical and palaeoflood records suggests that the flood signal reconstructed from Lago Inferiore de Laures sediments represents the regional and (multi-)decadal variability of summer–autumn floods well, in connection to Mediterranean mesoscale precipitation events. Overall, our results reveal the high potential of Lago Inferiore de Laures sediments to extend the regional earthquake and flood catalogues far back in time.

scholarly journals Unification of data from various seismic catalogues to study seismic activity in the Carpathians Mountain arc

2019 ◽  
Vol 11 (1) ◽  
pp. 837-842
Author(s):  
Agnieszka Braclawska ◽  
Adam Filip Idziak
Keyword(s):  
Central Europe ◽  
Seismic Data ◽  
Seismic Activity ◽  
Earthquake Catalogue ◽  
Active Area ◽  
Seismic Events ◽  
Large Area ◽  
Carpathian Mountains ◽  
The Carpathians ◽  
Seismic Networks

Abstract The Carpathian Mountainsarc is the most seismically active area in Central Europe. Analysis of the seismicity of entire Carpathian arc requires data from each of the particular catalogues which have to be properly and uniformly entered, standardized and merged. For our study we first had to prepare a database of seismic events (ML ≥ 1.6) compiled from the data of earthquakes taken from individual national seismic networks as well as data from international seismic centers. However, a careful review of these catalogues has uncovered significant inconsistencies, particularly discrepancies in the description of the location, magnitude and completeness of seismic events. To address these inconsistencies, a newly created compound earthquake catalogue was compiled from the aforementioned seismic catalogues and included events that occurred in the Carpathian Mountains arc area between 1976 and 2017. This work is intended to point out some of the problems associated with collecting data from various seismic catalogues as well as the need for their very careful verification, in order to create a uniform set of seismic data across a large area spanning numerous countries. The results suggest that compiling a uniform and dependable earthquake catalogue is crucial for reliable seismic studies.

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