scholarly journals The contribution of the NEMO-SN1 seafloor observatory to improve the seismic locations in the Ionian Sea (Italy)

2021 ◽  
Vol 64 (Vol. 64 (2021)) ◽  
Author(s):  
Tiziana Sgroi ◽  
Graziella Barberi ◽  
Alessandro Marchetti
Keyword(s):  
Structural Model ◽  
Single Point ◽  
Oceanic Lithosphere ◽  
P Wave ◽  
Ionian Sea ◽  
Offshore Area ◽  
Crustal Earthquakes ◽  
Mt Etna ◽  
Seismogenic Structures ◽  
Seafloor Observatory

The Western Ionian Sea is characterised by an active and diffuse seismicity, directly related to the convergence of the European and African Plates and by gravitational sinking and rollback of the  oceanic lithosphere. In this area, the location of earthquakes is characterised by considerable uncertainties due to large azimuthal gaps, resulting in notable location errors. This problem was  partially overcome with the use of data recorded by NEMO-SN1 seafloor observatory (October 2002 February 2003; June 2012 - May 2013). We relocated 1130 crustal and sub-crustal earthquakes  using land network and NEMO-SN1 data. As most events occurred on Mt. Etna, we focused on 358  earthquakes in the offshore area and near the coasts of Sicily and Calabria. The use of the combined  land-marine networks has improved the earthquake locations in terms of azimuthal GAP, as well as  in horizontal and vertical errors. The comparison between locations performed with and without NEMO-SN1 data shows that differences in latitude, longitude and depths are more evident in the Western Ionian Sea and in the coast of Sicily, where values of the differences over 5 km correspond  to structural heterogeneities. The increased number of seismic stations deployed on land from 2003  to 2012 did not influence the location of events occurring offshore, where NEMO-SN1 continued to be the distinctive tool in the location process. Moreover, the new 73 focal mechanisms computed with  P-wave polarities from NEMO-SN1 and land stations are in agreement with the regional structural   model, showing a prevalent normal, normal/oblique, and strike-slip kinematics. The similarity of two   new focal solutions with the mechanisms of the main shock and aftershock of the 1990 earthquake  demonstrates that the seismic structures are still active and potentially dangerous. The P-wave travel- time residual analysis confirms the activity along the main structural alignments.  A single point of observation in the Ionian Sea can significantly improve the quality of locations, giving an opportunity to focus on the seismogenic structures responsible for the occurrence of  medium-to-high magnitude earthquakes.

scholarly journals No mafic layer in 80 km thick Tibetan crust

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gaochun Wang ◽  
Hans Thybo ◽  
Irina M. Artemieva
Keyword(s):  
Seismic Data ◽  
P Wave ◽  
Indian Plate ◽  
Low Velocity ◽  
Crustal Earthquakes ◽  
Tectonic Processes ◽  
P Wave Velocity ◽  
Juvenile Crust ◽  
Mafic Lower Crust ◽  
Thick Crust

AbstractAll models of the magmatic and plate tectonic processes that create continental crust predict the presence of a mafic lower crust. Earlier proposed crustal doubling in Tibet and the Himalayas by underthrusting of the Indian plate requires the presence of a mafic layer with high seismic P-wave velocity (Vp > 7.0 km/s) above the Moho. Our new seismic data demonstrates that some of the thickest crust on Earth in the middle Lhasa Terrane has exceptionally low velocity (Vp < 6.7 km/s) throughout the whole 80 km thick crust. Observed deep crustal earthquakes throughout the crustal column and thick lithosphere from seismic tomography imply low temperature crust. Therefore, the whole crust must consist of felsic rocks as any mafic layer would have high velocity unless the temperature of the crust were high. Our results form basis for alternative models for the formation of extremely thick juvenile crust with predominantly felsic composition in continental collision zones.

scholarly journals Isochronal maps at Mt. Etna volcano (Italy): a simple and reliable tool for investigating large-scale heterogeneities

1997 ◽  
Vol 40 (5) ◽  
Author(s):  
G. Patanè ◽  
C. Centamore ◽  
S. La Delfa
Keyword(s):  
Large Scale ◽  
Volcanic Edifice ◽  
P Wave ◽  
Etna Volcano ◽  
Low Velocity ◽  
Seismic Stations ◽  
Arrival Times ◽  
Mt Etna ◽  
Wave Arrival ◽  
Feeding Systems

This paper analyses twelve etnean earthquakes which occurred at various depths and recorded at least by eleven stations. The seismic stations span a wide part of the volcanic edifice; therefore each set of direct P-wave arrival times at these stations can be considered appropriate for tracing isochronal curves. Using this simple methodology and the results obtained by previous studies the authors make a reconstruction of the geometry of the bodies inside the crust beneath Mt. Etna. These bodies are interpreted as a set of cooled magmatic masses, delimited by low-velocity discontinuities which can be considered, at present, the major feeding systems of the volcano.

On the ratio of P-wave to S-wave corner frequencies for shallow earthquake sources

1974 ◽  
Vol 64 (4) ◽  
pp. 1159-1180 ◽  
Author(s):  
F. A. Dahlen
Keyword(s):  
Single Point ◽  
Three Dimensional ◽  
P Wave ◽  
Corner Frequency ◽  
S Wave ◽  
Earthquake Sources ◽  
Kinematical Model ◽  
Self Similar ◽  
Smooth Deceleration ◽  
Shallow Focus

abstract We construct a theoretical three-dimensional kinematical model of shallow-focus earthquake faulting in order to investigate the ratio of the P- and S-wave corner frequencies of the far-field elastic radiation. We attempt to incorporate in this model all of the important gross kinematical features which would arise if ordinary mechanical friction should be the dominant traction resisting fault motion. These features include a self-similar nucleation at a single point, a subsonic spreading of rupture away from that point, and a termination of faulting by smooth deceleration. We show that the ratio of the P-wave corner frequency to the S-wave corner frequency for any model which has these features will be less than unity at all points on the focal sphere.

scholarly journals A multicomponent Isabella anomaly: Resolving the physical state of the Sierra Nevada upper mantle from Vp/Vs anisotropy tomography

Geosphere ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 2018-2042 ◽  
Author(s):  
Melissa V. Bernardino ◽  
Craig H. Jones ◽  
William Levandowski ◽  
Ian Bastow ◽  
Thomas J. Owens ◽  
...  
Keyword(s):  
Sierra Nevada ◽  
Upper Mantle ◽  
Oceanic Lithosphere ◽  
P Wave ◽  
Wave Speeds ◽  
High Wave ◽  
The Core ◽  
High Speeds ◽  
Great Valley ◽  
Isabella Anomaly

Abstract The Isabella anomaly, a prominent upper-mantle high-speed P-wave anomaly located within the southern Great Valley and southwestern foothills of the Sierra Nevada, has been interpreted either as foundering sub-Sierran lithosphere or as remnant oceanic lithosphere. We used Vp/Vs anisotropy tomography to distinguish among the probable origins of the Isabella anomaly. S waveforms were rotated into the Sierran SKSFast and SKSSlow directions determined from SKS-splitting studies. Teleseismic P-, SFast-, SSlow-, SKSFast-, and SKSSlow-wave arrival times were then inverted to obtain three-dimensional (3-D) perturbations in Vp, Vp/VsMean, and percent azimuthal anisotropy using three surface wave 3-D starting models and one one-dimensional (1-D) model. We observed the highest Vp/Vs anomalies associated with slower velocities in regions marked by young volcanism, with the largest of these anomalies being the Mono anomaly under the Long Valley region, which extends to depths of at least 75 km. Peak Vp/Vs perturbations of +4% were found at 40 km depth. The low velocities and high Vp/Vs values of this anomaly could be related to partial melt. The high wave speeds of the Isabella anomaly coincide with low Vp/Vs values with peak perturbations of −2%, yet they do not covary spatially. The P-wave inversion imaged the Isabella anomaly as a unimodal eastward-plunging body. However, the volume of that Isabella anomaly contains three separate bodies as defined by varying Vp/Vs values. High speeds, regionally average Vp/Vs values (higher than the other two anomalies), and lower anisotropy characterize the core of the Isabella anomaly. The western and shallowest part has high wave speeds and lower Vp/Vs values than the surrounding mantle. The eastern and deepest part of the anomaly also contains high speeds and lower Vp/Vs values but exhibits higher anisotropy. We considered combinations of varying temperature, Mg content (melt depletion), or modal garnet to reproduce our observations. Our results suggest that the displaced garnet-rich mafic root of the Mesozoic Sierra Nevada batholith is found in the core of the Isabella anomaly. If remnant oceanic lithosphere exists within the Isabella anomaly, it most likely resides in the shallow, westernmost feature. Within the Sierra Nevada, the highest upper-mantle anisotropy is largely contained within the central portion of the range and the adjacent Great Valley. Anisotropy along the Sierra crest is shallow and confined to the lithosphere between 20 and 40 km depth. Directly below, there is a zone of low anisotropy (from 170 to 220 km depth), low velocities, and high Vp/Vs values. These features suggest the presence of vertically upwelling asthenosphere and consequent horizontal flow at shallower depths. High anisotropy beneath the adjacent western foothills and Great Valley is found at ∼120 km depth and could represent localized mantle deformation produced as asthenosphere filled in a slab gap.

Seismotectonic setting of Santorini-Amorgos zone and the surrounding area revealed from crustal earthquakes relocation and Vp/Vs distribution

2020 ◽  
Author(s):  
Ratri Andinisari ◽  
Konstantinos I. Konstantinou ◽  
Pratul Ranjan ◽  
Qori F. Hermawan
Keyword(s):  
Cross Correlation ◽  
Double Difference ◽  
Surrounding Area ◽  
Submarine Volcano ◽  
S Wave ◽  
Offshore Area ◽  
Crustal Earthquakes ◽  
Wave Travel ◽  
Seismic Networks ◽  
Earthquake Clusters

&lt;p&gt;The Santorini-Amorgos zone represents right-lateral transtensional regime from NE of Santorini to the south of Amorgos which also hosts Kolumbo submarine volcano. A total number of 1869 crustal events from 2002 to 2019 were recorded by permanent and temporal seismic networks deployed in southern Aegean. Absolute locations of these events were obtained by utilizing the probabilistic nonlinear algorithm NonLinLoc. Precise relative relocation by using double-difference algorithm with catalog and cross-correlation differential times was later performed, resulting in 1455 locations with horizontal and vertical uncertainties of less than 0.3 km. Clusters of earthquakes relocated between Naxos and Paros as well as north of Astypalaia do not coincide with any fault in the area. Similarly, the relocated crustal events across Santorini-Amorgos zone show that most of the earthquake clusters do not coincide with any of the existing faults. The distribution of Vp/Vs ratios in the area were investigated based on the P and S-wave travel times of all the events. Vp/Vs ratios in the area vary between 1.67 and 2.03 with errors less than 0.04. The highest Vp/Vs values were found to be distributed in the area between Naxos and Paros. Other areas with notably high Vp/Vs ratio are north of Santorini, Anydros, west of Amorgos, offshore area south of the easternmost tip of Amorgos, and the island of Astypalaia. These mentioned areas were also rich in seismic activities during the period of study. The high Vp/Vs ratios in the region of high seismicity signifies that these events were likely related to the migration of magmatic fluids to the surface and may not be caused by the existing faults.&lt;/p&gt;

scholarly journals New observations of local seismicity by the SN-1 seafloor observatory in the Ionian Sea, off-shore Eastern Sicily (Italy)

2007 ◽  
Vol 169 (2) ◽  
pp. 490-501 ◽  
Author(s):  
Tiziana Sgroi ◽  
Laura Beranzoli ◽  
Giuseppe Di Grazia ◽  
Andrea Ursino ◽  
Paolo Favali
Keyword(s):  
Ionian Sea ◽  
Local Seismicity ◽  
Seafloor Observatory

scholarly journals Population Pharmacokinetics of Ciprofloxacin in Pediatric and Adolescent Patients with Acute Infections

2003 ◽  
Vol 47 (10) ◽  
pp. 3170-3178 ◽  
Author(s):  
S. Payen ◽  
R. Serreau ◽  
A. Munck ◽  
Y. Aujard ◽  
Y. Aigrain ◽  
...  
Keyword(s):  
Population Pharmacokinetics ◽  
Structural Model ◽  
Single Point ◽  
Clinical Status ◽  
Sampling Strategy ◽  
Accurate Estimation ◽  
Pharmacokinetic Parameters ◽  
Treatment Schedule ◽  
Mixed Effect ◽  
Limited Sampling

ABSTRACT The aim of the present study was to characterize the population pharmacokinetics of ciprofloxacin in patients with and without cystic fibrosis ranging in age from 1 day to 24 years and to propose a limited sampling strategy to estimate individual pharmacokinetic parameters. Patients were divided into four groups according to the treatment schedule. They received ciprofloxacin by intravenous infusion (30 min) or by the oral route. The number of samples collected from each patient ranged from 1 to 12. The population parameters were computed for an initial group of 37 patients. The data were analyzed by nonlinear mixed-effect modeling by use of a two-compartment structural model. The interindividual variability in clearance (CL) was partially explained by a dependence on age and the patient's clinical status. In addition, a significant relationship was found between weight and the initial volume of distribution. Eighteen additional patients were used for model validation and evaluation of limited sampling strategies. When ciprofloxacin was administered intravenously, sampling at a single point (12 h after the start of infusion) allowed the precise and accurate estimation of CL and the elimination half-life, as well as the ciprofloxacin concentration at the end of the infusion. It should be noted that to take into account the presence of a lag time after oral administration, a schedule based on two sampling times of 1 and 12 h is needed. The results of this study combine relationships between ciprofloxacin pharmacokinetic parameters and patient covariates that may be useful for dose adjustment and a convenient sampling procedure that can be used for further studies.

scholarly journals Two subduction-related heterogeneities beneath the Eastern Alps and the Bohemian Massif imaged by high-resolution P-wave tomography

2021 ◽  
Author(s):  
Jaroslava Plomerová ◽  
Helena Žlebčíková ◽  
György Hetényi ◽  
Luděk Vecsey ◽  
Vladislav Babuška ◽  
...  
Keyword(s):  
High Resolution ◽  
Bohemian Massif ◽  
High Velocity ◽  
Oceanic Lithosphere ◽  
Eastern Alps ◽  
P Wave ◽  
Tomographic Images ◽  
The North ◽  
Wave Tomography ◽  
Seismic Networks

Abstract. We present high-resolution tomographic images of the upper mantle beneath the E. Alps and the adjacent Bohemian Massif (BM) in the North based on data from the AlpArray-EASI and AlpArray Seismic Networks. The tomography locates the Alpine high-velocity perturbations between the Periadriatic Lineament and the Northern Alpine Front. The northward-dipping lithosphere keel is imaged down to ~200–250 km depth, without signs of delamination, and we associate it with the Adriatic plate subduction. Detached high-velocity heterogeneity, sub-parallel to and distinct from the E. Alps heterogeneity is imaged at ~100–200 km depths beneath the southern part of the BM. We associate this heterogeneity with the western end of a SW-NE striking heterogeneity beneath the south-eastern part of the BM, imaged in models of larger extent. The strike, parallel with the Moldanubian/Brunovistulian mantle-lithosphere boundary in the BM and with the westernmost part of the Carpathian front, lead us to consider potential scenarios relating the heterogeneity to (1) a remnant of the delaminated European plate, (2) a piece of continental-and-oceanic lithosphere mixture related to the building of the BM, particularly to the closure of the old Rheic ocean during the MD/BV collision or (3) a lithospheric fragment going through to the NW between the E. Alps and W. Carpathians fronts in a preceding subduction phase. The study is dedicated to our outstanding and respected colleague Vladislav Babuška, who coined innovative views on the European lithosphere and died on March 30, 2021.

scholarly journals Volcanic Tremor of Mt. Etna (Italy) Recorded by NEMO-SN1 Seafloor Observatory: A New Perspective on Volcanic Eruptions Monitoring

Geosciences ◽  
2019 ◽  
Vol 9 (3) ◽  
pp. 115
Author(s):  
Tiziana Sgroi ◽  
Giuseppe Di Grazia ◽  
Paolo Favali
Keyword(s):  
Gravity Waves ◽  
Volcanic Tremor ◽  
Volcanic Eruptions ◽  
Seismic Signal ◽  
High Amplitude ◽  
Sea Waves ◽  
Spectral Content ◽  
Mt Etna ◽  
New Perspective ◽  
Seafloor Observatory

The NEMO-SN1 seafloor observatory, located 2100 m below sea level and about 40 km from Mt. Etna volcano, normally records a background seismic signal called oceanographic noise. This signal is characterized by high amplitude increases, lasting up to a few days, and by two typical 0.1 and 0.3 Hz frequencies in its spectrum. Particle motion analysis shows a strong E-W directivity, coinciding with the direction of sea waves; gravity waves induced by local winds are considered the main source of oceanographic noise. During the deployment of NEMO-SN1, the vigorous 2002–2003 Mt. Etna eruption occurred. High-amplitude background signals were recorded during the explosive episodes accompanying the eruption. The spectral content of this signal ranges from 0.1 to 4 Hz, with the most powerful signal in the 0.5–2 Hz band, typical of an Etna volcanic tremor. The tremor recorded by NEMO-SN1 shows a strong NW-SE directivity towards the volcano. Since the receiver is underwater, we inferred the presence of a circulation of magmatic fluids extended under the seafloor. This process is able to generate a signal strong enough to be recorded by the NEMO-SN1 seafloor observatory that hides frequencies linked to the oceanographic noise, permitting the offshore monitoring of the volcanic activity of Mt. Etna.

Travel times from central Pacific nuclear explosions and inferred mantle structure

1964 ◽  
Vol 54 (6B) ◽  
pp. 2271-2294
Author(s):  
Dean S. Carder
Keyword(s):  
Single Point ◽  
P Wave ◽  
Graphical Form ◽  
Travel Times ◽  
Time Data ◽  
Central Pacific ◽  
Arrival Times ◽  
Nuclear Explosions ◽  
Straight Line ◽  
Travel Time Data

Abstract Travel time data, from widely recorded nuclear detonations in the Eniwetok and Bikini atolls of the central Pacific, have been compiled and are presented. Although a number of stations recorded ten or more events from each atoll, the resulting data may be considered as from a single point source, precisely known in time and place. Composite P-wave travel times are presented in a graphical form and, in the distance range from 3 to 102 degrees, are represented as eight near straight-line segments. P-wave speeds in the top of the mantle average about 8.2 km/sec to distances beyond 17 degrees, and a sharp discontinuity at 19.5 degrees is indicated. There is no evidence for or against a low-speed layer in the upper mantle nor for a regional shadow zone. A mantle model consisting of a number of discrete spherical shells has been constructed. A core depth of 2,870 km, 30 km short of the accepted value, is calculated from PcP arrival times at Matsushiro and College, which are 2.5 and 3.5 sec. earlier than are indicated in the Jeffreys-Bullen tables.

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