Development and Testing of Seismic Regional Discriminants

The routine process of the IMS data at the CTBTO International Data Center (IDC) is aimed at identifying in the seismological bulletins all the seismic events the source of which is certainly natural. This process, named screening out, is carried out on several tens of earthquakes per day. It is important that the methods used for the screening process are as reliable and efficient as possible, so as substantially reducing the number of suspicious events without classifying any explosion as natural events. The principal identification method applied at the CTBTO IDC is based on the difference between the Ms magnitude, computed from the amplitude of the surface Rayleigh waves with period close to 20 s, and the mb magnitude computed from the amplitude of the body waves with period close to 1 s. The applicability of this method is, however, limited by the difficulty of detecting surface waves for events of low mb magnitudes, so as to allow the computation the Ms magnitude for such events, which are very numerous. For CTBT verification, in case of events of small magnitude, the use of stations at regional distances from the epicenter, is crucial. In this context, another category of seismological screening, the so-called regional discriminants, can be applied. This method is based on the amplitudes of the surface waves (Lg) at much higher frequencies (8-12 Hz). Unfortunately, these high-frequency waves are not easily detectable, and the method requires regional calibration curves for each specific site, calibrations that are not available on a global scale

TRAVEL-TIME SOURCE SPECIFIC STATION CORRECTION IMPROVES LOCATION ACCURACY

Accurate earthquake locations are crucial for investigating seismogenic processes, as well as for applications like verifying compliance to the Comprehensive Test Ban Treaty (CTBT). Earthquake location accuracy is related to the degree of knowledge about the 3-D structure of seismic wave velocity in the Earth. It is well known that modeling errors of calculated travel times may have the effect of shifting the computed epicenters far from the real locations by a distance even larger than the size of the statistical error ellipses, regardless of the accuracy in picking seismic phase arrivals. We have developed a method of seismic location to minimize this systematic shifts affecting hypocentral locations. These method is based on the fact that such shifts are quite similar for events for which the hypocenters are close to each other with respect to their distance from the recording stations. So this method is based on a set of Ground Truth events recorded by a dense local seismic network in seismically active regions. The applications concern seismic sequences recorded in Italy and Iran. We show that mislocations of the order of 10-20 km affecting the epicenters, as well as larger mislocations in hypocentral depths, calculated from a global seismic network can be effectively removed by applying source-specific station corrections applied to the standard IASPEI91 travel times. This method is valid only for the area where calibration events are located but it is valid for any subset of the station network used for the calibration

Aeromagnetic anomalies reveal hidden tectonic and volcanic structures in the Aeolian Islands, southern Tyrrhenian Sea, Italy

The structures of the Southern Tyrrhenian Sea active volcanoes have been successfully investigated through the use of the magnetic data. Particularly, several high resolution aeromagnetic campaigns have been carried out on the Aeolian Archipelago and its western limit by the Airborne Geophysics Science Team of Istituto Nazionale di Geofisica e Vulcanologia of Roma. The results indicate that the volcanism is controlled by tectonic structures both at local and regional scale. The emplacement of magnetized bodies (e.g. volcanic conduits, dikes swarms, intrusions) is along or strictly correlated with this tectonic framework. The consolidation of highly magnetized material inside the volcanic conduits determines contrast with surrounding less magnetized material producing intense magnetic anomalies. Therefore, modeling of these sources is suggestive of the position and deep extent of eruptive vents, especially in the offshore area, where we do not know where future submarine activity may take place (De Ritis et al., 2005). We present here a case study were the magnetic tool resolved a geological interpretative problem that was not settled earlier. In fact, in the Calabria mainland, widespread, dacitic to rhyolitic pumices with calc-alkaline affinity of Pleistocene age (1-0.7 Ma) are exposed. The tephra falls are related to explosive activity and show thickness decreasing from the Capo Vaticano area southeastward. The lithics indicate a source located not far from Capo Vaticano. The interpretation of the magnetic anomaly field together with the other geological and geophysical data has allowed to discover the presence of a previously unknown volcanic structure (De Ritis et al., 2010), very close to the Calabria Western coast (Capo Vaticano). Aeromagnetic data collected between the Panarea island and the Calabria arc highlight a WNW-ESE elongated positive magnetic anomaly centered on the Capo Vaticano morphological ridge. Forward and inverse modeling show a magnetized body extending from the bathymetric surface to about 3 km of depth. The magnetic properties of such a body are consistent with those of the medium to highly evolved volcanic rocks of the Aeolian Arc, i.e. dacites and rhyolites. The combined interpretation of the magnetic and available geological data reveal that (1) the Capo Vaticano WNW- ESE elongated positive magnetic anomaly is due to the occurrence of a WNW-ESE elongated sill; (2) such a sill represents the remnant of the plumbing system of a Pleistocene volcano that erupted explosively producing the pumice tephra exposed in Calabria; and (3) the volcanism is consistent with the Aeolian products, in terms of age, magnetic signature, and geochemical affinity of the erupted products. The results indicate that such volcanism developed along seismically active faults transversal to the general trend of the Aeolian Arc and Calabria block, in an area where uplift is maximized (4 mm/yr). Such uplift could also be responsible for fragmentation of the upper crust and formation of transversal faults along which seismic activity and volcanism occur

An alternative 3D inversion method for magnetic anomalies with depth resolution

This paper presents a new method to invert magnetic anomaly data in a variety of non-complex contexts when a priori information about the sources is not available. The region containing magnetic sources is discretized into a set of homogeneously magnetized rectangular prisms, polarized along a common direction. The magnetization distribution is calculated by solving an underdetermined linear system, and is accomplished through the simultaneous minimization of the norm of the solution and the misfit between the observed and the calculated field. Our algorithm makes use of a dipolar approximation to compute the magnetic field of the rectangular blocks. We show how this approximation, in conjunction with other correction factors, presents numerous advantages in terms of computing speed and depth resolution, and does not affect significantly the success of the inversion. The algorithm is tested on both synthetic and real magnetic datasets

A Multidisciplinary Study of the DPRK Nuclear Tests

The Democratic People Republic of Korea announced two underground nuclear tests carried out in their territory respectively on October 9th, 2006 and May 25th, 2009. The scarce information on the precise location and the size of those explosions has stimulated various kinds of studies, mostly based on seismological observations, by several national agencies concerned with the Nuclear Test Ban Treaty verification. We analysed the available seismological data collected through a global high-quality network for the two tests. After picking up the arrival times at the various stations, a standard location program has been applied to the observed data. If we use all the available data for each single event, due to the different magnitude and different number of available stations, the locations appear quite different. On the contrary, if we use only the common stations, they happen to be only few km apart from each other and within their respective error ellipses. A more accurate relative location has been carried out by the application of algorithms such as double difference joint hypocenter determination (DDJHD) and waveform alignment. The epicentral distance between the two events obtained by these methods is 2 km, with the 2006 event shifted to the ESE with respect to that of 2009. We then used a dataset of VHR TerraSAR-X satellite images to detect possible surface effects of the underground tests. This is the first ever case where these highly performing SAR data have been used to such aim. We applied InSAR processing technique to fully exploit the capabilities of SAR data to measure very short displacements over large areas. Two interferograms have been computed, one co-event and one post-event, to remove possible residual topographic signals. A clear displacement pattern has been highlighted over a mountainous area within the investigated region, measuring a maximum displacement of about 45 mm overall the relief. Hypothesizing that the 2009 nuclear test had been carried out close to the area where the displacement has been observed through the DInSAR technique, its relation with the epicenter location obtained through seismological processing has been discussed as a possible alternative hypothesis with respect to the preferred solutions reported by the nuclear explosion database (NEDB). The distance of about 10 km between the two places can be considered acceptable in light of the possible systematic location shifts commonly observed in the seismological practice over a global scale. The difference between the m b magnitudes of the two tests could reflect differences in geological conditions of the two test sites, even if the yield of the two explosions had been the same

Inverse Modelling of the Reversely Magnetized, Shallow Plumbing System Hosting Oil Reservoirs of the Auca Mahuida Volcano (Payeina retroarc, Neuquén Basin, Argentina)

The Auca Mahuida volcano (2.03–0.88 Ma) located east of the Andean thrust front in the Neuquén basin (Argentina) hosts an oil system of thermogenic origin and is affected by the NW–SE striking-faults. Intrusive bodies and the underlying Jurassic sediments constitute the reservoir rocks. Aeromagnetic data collected in the Auca Mahuida area detected multiple dipolar magnetic anomalies, many of which have reverse polarity. Palaeomagnetic measurements on rock samples collected in the field together with available age determinations indicate that the reversely magnetized sources were mainly emplaced during the Matuyama reverse polarity chron while the normal polarity sources were emplaced during the Olduvai and/or Jaramillo subchrons. The location and geometry of the intrusive bodies is poorly known and the customary magnetic inversion is rendered difficult because of multiple natural remanent magnetization directions. To address these difficulties, a voxel inversion was applied to model the vector residual magnetic intensity (VRMI) transformation of the observed total magnetic intensity data. The modelling showed a 1.5 km deep, subcircular ring-shaped intrusion below the summit of the volcano and a series of NW–SE elongated, fault-controlled intrusive bodies to depths up to 3–4 km. Our results show that magnetic data and VRMI modelling help resolve the geometry of the shallow plumbing system of volcanoes with remanently magnetized sources, and estimate the depth and geometry of potential oil reservoirs in volcanic areas

Aeromagnetic anomaly images of Vulcano and Southern Lipari Islands (Aeolian Archipelago, Italy)

Newly acquired high-resolution, low-altitude aeromagnetic data over Vulcano Island and Southwestern Lipari in the Southern Tyrrhenian Sea resolve the major volcanic features in the area associated with the past and present activity. The magnetic character changes in amplitude and frequency from south-east to north-west. The Primordial Vulcano, the Lentia Complex, the Piano Caldera units, the Fossa Caldera deposits, and the currently active La Fossa cone and Vulcanello represent the main volcanic phases on Vulcano Island. They show a distinct magnetic anomaly pattern, whereas prior to this survey, no magnetic signatures of these features were found

Brexpiprazole as a new approach of treatment in somatization disorder

© 2022 Published by Elsevier Ltd on behalf of International Society for the Study of Emerging Drugs. This is an open access article under the CC-BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)Introduction: Somatic symptom disorder (SSD) is a mental disorder that involves one or more physical symptoms (e.g. palpitations, dizziness, diarrhoea, limb weakness, pain, and pseudo neurological symptoms) accompanied by one or more thoughts, feelings, and/or behaviours related to the somatic symptom(s) resulting in significant distress and/or dysfunction lasting for more than 6 months. At now the SSD can be refractory to psychiatric intervention including antidepressants, antiepileptics, and antipsychotics as well as the effectiveness of many of these treatments is limited. The objective of this study was to report the effectiveness of a third-generation antipsychotic drug brexpiprazole for treatment of a case of SSD together with the serotonin selective reuptake inhibitor (SSRI) fluvoxamine. Methods: A single case study of a 59-year-old female with SSD was here performed. Findings: After 4 weeks of treatment brexpiprazole, together with lamotrigine and fluvoxamine, was here effective in decreasing both depressive and anxiety symptoms, normalising previous unusual thought contents and of related behaviours. The patient reported an overall good response and started to function again in important domains of life. No adverse events occurred. Conclusion: To our knowledge, this is the first case showing Brexpiprazole effective for the treatment of a case of SSD as add-on to other drugs.Peer reviewedFinal Published versio