The Deformation of Active Tectonic Blocks on the Chinese Mainland and Its Relationship with Seismic Activity

Based on the hypothesis of the active tectonic blocks on the Chinese continent and its adjacent regions (both the method of the DDA on a spherical surface and the GPS survey results observed from 1991 to 2001 are used), the movements and deformations of each active tectonicblock are calculated. The calculation results show that although the movements and deformations of active tectonic-blocks in the eastern region and in the western region of China are different, active tectonic blocks in the same active tectonic block region are coherent.Then, the relative velocities of the active tectonic-blocks‘ boundary zones are calculated, and the relationship between current crustal motion and strong seismic activities is discussed. Earthquakes (Ms≥7.0) on the Chinese continent since 1988 all occurred on boundary zones of active tectonic blocks with high slipping speed.     

Energy-4 Generator for Monitoring Seismically Active Regions and Electromagnetic Sounding of the Earth’s Crust. Experience of Application in the Kovdor-2015 Experiment

The first section of the paper describes the developed self-powered, chassis mounted mobile Energy-4 generator, which has a power of 29 kW and a maximum output voltage of up to 1200 V. The generator operates in the audio frequency range (2–2000 Hz) and is designed for electromagnetic sounding of the Earth’s upper crust in the search for minerals and monitoring of earthquake source zones in seismically active regions. The main power units of the generator are a PWM inverter and a step-up transformer. The inverter is powered by two DC generators mounted on the driveshaft of a truck, in the body of truck of which the generator is mounted. The circuit diagram and operation of the generator are considered, as well as individual design solutions that made it possible to increase the amplitude of the output voltage and, consequently, the current in grounded power lines. The second section is devoted to full-scale tests of the Energy-4 generator in the Kovdor-2015 experiment, during which multipath frequency soundings with 25 and 50 km spacings were carried out on the territory of the Enskii–Kovdor granite-gneiss complex composed of rocks of the Archaean basement of the Baltic Shield. As a result of the experiment, a ubiquitous intermediate conducting dilatancy-diffusion layer (DD layer) was found at depths from 2–3 to 5–9 km in an area of 100 × 200 km. The parameters of this layer have been investigated. The layer is considered a seismically active element of the brittle Earth’s upper crust with a thickness of 10–15 km.     

Regimes of magma recharge and their control on the eruptive behaviour during the period 2001–2005 at Mt. Etna volcano

Mount Etna volcano (Italy) during the period 2001–2005 has undergone a period of intense eruptive activity marked by three large eruptions (2001, 2002–2003 and 2004–2005). These eruptions encompassed diverse eruptive styles and regimes: from intensely explosive, during 2001 and 2002–2003 eruptions, to exclusively effusive in the 2004–2005 event. In this work, we put forward the idea that these three eruptions are the response of the progressive arrival into the uppermost segment of the open-conduit system of a new magma, which was geochemically distinct in terms of trace element and Sr–Nd–Pb isotope signature from the products previously emitted by the Etnean volcano. The magma migrated upwards mainly through a peripheral tectonic system, which can be considered as eccentric in spite of its relative proximity to the main system. The ingress of the new magma and its gradual displacement from the eccentric system into the uppermost sector of the open-conduit gave rise to different eruptive behaviours. At the beginning, the ascent of the undegassed magma, able to exsolve a gas phase at depth, and its interaction with closed-system magma reservoirs less than 10 km deep gave rise to the explosive events of 2001 and 2002–2003. Later, when the same magma entered into the open-conduit system, it took part in the steady-state degassing and partially lost its volatile load, leading to a totally effusive eruption during the 2004–2005 event. One further consideration highlighted here is that in 2001–2005, migration of the feeding axis from an eccentric and peripheral position towards the main open-conduit has led to the development of a new vent (South East Crater 2) located at the eastern base of the South East Crater through which most of the subsequent Etnean activity occurred.     

Analysis of Current Movements and Deformations of the Earth’s Crust in Fennoscandia from GNSS Data

Izvestiya, Physics of the Solid Earth - Abstract—An analysis of the displacement rates of GNSS points indicates that the values of current deformations gradually decrease from the center of...     

Correlation of variations in the thermal neutron flux from the Earth’s crust with the Moon’s phases and with seismic activity

The results of the long-term recording of thermal neutron flux near the Earth’s surface with the use of an unshielded scintillation thermal-neutron detector are presented. The data obtained indicate the presence of periodic variations in the thermal neutron flux with the lunar diurnal and the lunar monthly periods. A hypothesis about the existence in the Earth’s crust of radon-neutron tidal variations in the concentration of thermal neutrons, correlated with the Moon’s phases and which have the gravitational origin, is formulated and confirmed experimentally. A simple mathematical model is proposed, which satisfactorily describes the observed variations. The case of the anomalous behavior of thermal neutrons is presented, which correlates with the high local seismic activity.     

Lava channel roofing,overflows, breaches and switching: insights from the 2008–2009 eruption of Mt. Etna

During long-lived basaltic eruptions, overflows from lava channels and breaching of channel levées are important processes in the development of extensive 'a'ā lava flow-fields. Short-lived breaches result in inundation of areas adjacent to the main channel. However, if a breach remains open, lava supply to the original flow front is significantly reduced, and flow-field widening is favoured over lengthening. The development of channel breaches and overflows can therefore exert strong control over the overall flow-field development, but the processes that determine their location and frequency are currently poorly understood. During the final month of the 2008–2009 eruption of Mt. Etna, Sicily, a remote time-lapse camera was deployed to monitor events in a proximal region of a small ephemeral lava flow. For over a period of ~10 h, the flow underwent changes in surface elevation and velocity, repeated overflows of varying vigour and the construction of a channel roof (a required prelude to lava tube formation). Quantitative interpretation of the image sequence was facilitated by a 3D model of the scene constructed using structure-from-motion computer vision techniques. As surface activity waned during the roofing process, overflow sites retreated up the flow towards the vent, and eventually, a new flow was initiated. Our observations and measurements indicate that flow surface stagnation and flow inflation propagated up-flow at an effective rate of ~6 m h⁻¹, and that these processes, rather than effusion rate variations, were ultimately responsible for the most vigorous overflow events. We discuss evidence for similar controls during levée breaching and channel switching events on much larger flows on Etna, such as during the 2001 eruption.     

Comment on the paper “The Relationship between Multifractal and Entropy Properties of Seismic Noise in Kamchatka and Irregularity of the Earth’s Rotation” by A.A. Lyubushin,G.N. Kopylova,and Yu.K. Serafimova

Izvestiya, Physics of the Solid Earth - Abstract—In my comment on the paper by A.A. Lyubushin, G.N. Kopylova, and Yu.K. Serafimova, I focus on the problem of legitimacy of seismological data...     

Method for Determining the Ultimate Strain for Rocks of the Earth’s Crust from the Magnitude of Relative Slips on the Earth’s Surface after a Strong Earthquake

The ultimate strain value for rocks in aggregate with their other physicomechanical characteristics plays a substantial role when solving different problems related to the bearing capacity and behavior of soils. These include determination of the maximum displacement, velocity, and acceleration values of soils during earthquakes and estimation of the potential strain energy accumulated in a medium during strong earthquake preparation. The latter parameter is also key in predicting earthquakes from the ultimate strain of rocks. The paper describes a technique developed by the author for determining the ultimate strain of soil columns under natural conditions from their relative slope on the surface after a strong earthquake. The empirical dependences of the ultimate strain of rocks on earthquake magnitude, relative slip, rupture length, and the seismic moment are obtained by analyzing their values calculated by the proposed method for 44 strong earthquakes with magnitudes of 5.6–8.5. A comparative analysis of the ultimate strain values obtained by other researchers by geodesic triangulation is performed.     

Gradual Fault Weakening with Seismic Slip: Inferences from the Seismic Sequences of L’Aquila, 2009, and Northridge, 1994

We estimate seismological fracture energies from two subsets of events selected from the seismic sequences of L’Aquila (2009), and Northridge (1994): 57 and 16 selected events, respectively, including the main shocks. Following Abercrombie and Rice (Geophys J Int 162: 406–424, 2005), we postulate that fracture energy (G) represents the post-failure integral of the dynamic weakening curve, which is described by the evolution of shear traction as a function of slip. Following a direct-wave approach, we compute mainshock-/aftershock-source spectral ratios, and analyze them using the approach proposed by Malagnini et al. (Pure Appl. Geophys., this issue, 2014) to infer corner frequencies and seismic moment. Our estimates of source parameters (including fracture energies) are based on best-fit grid-searches performed over empirical source spectral ratios. We quantify the source scaling of spectra from small and large earthquakes by using the MDAC formulation of Walter and Taylor (A revised Magnitude and Distance Amplitude Correction (MDAC2) procedure for regional seismic discriminants, 2001). The source parameters presented in this paper must be considered as point-source estimates representing averages calculated over specific ruptured portions of the fault area. In order to constrain the scaling of fracture energy with coseismic slip, we investigate two different slip-weakening functions to model the shear traction as a function of slip: (i) a power law, as suggested by Abercrombie and Rice (Geophys J Int 162: 406–424, 2005), and (ii) an exponential decay. Our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies, both for the main events and for their aftershocks, regardless of the significant differences in the energy budgets between the large (main) and small earthquakes (aftershocks). Using the power-law slip-weakening function would lead us to a very different situation: in our two investigated sequences, if the aftershock scaling is extrapolated to events with large slips, a power law (a la Abercrombie and Rice) would predict unrealistically large stress drops for large, main earthquakes. We conclude that the exponential stress evolution law has the advantage of avoiding unrealistic stress drops and unbounded fracture energies at large slip values, while still describing the abrupt shear-stress degradation observed in high-velocity laboratory experiments (e.g., Di Toro et al., Fault lubrication during earthquakes, Nature 2011).     

Petrology of lavas from the 2004–2005 flank eruption of Mt. Etna,Italy: inferences on the dynamics of magma in the shallow plumbing system

Following the 2001 and 2002–2003 flank eruptions, activity resumed at Mt. Etna on 7 September 2004 and lasted for about 6 months. This paper presents new petrographic, major and trace element, and Sr–Nd isotope data from sequential samples collected during the entire 2004–2005 eruption. The progressive change of lava composition allowed defining three phases that correspond to different processes controlling magma dynamics inside the central volcano conduits. The compositional variability of products erupted up to 24 September is well reproduced by a fractional crystallization model that involves magma already stored at shallow depth since the 2002–2003 eruption. The progressive mixing of this magma with a distinct new one rising within the central conduits is clearly revealed by the composition of the products erupted from 24 September to 15 October. After 15 October, the contribution from the new magma gradually becomes predominant, and the efficiency of the mixing process ensures the emission of homogeneous products up to the end of the eruption. Our results give insights into the complex conditions of magma storage and evolution in the shallow plumbing system of Mt. Etna during a flank eruption. Furthermore, they confirm that the 2004–2005 activity at Etna was triggered by regional movements of the eastern flank of the volcano. They caused the opening of a complex fracture zone extending ESE which drained a magma stored at shallow depth since the 2002–2003 eruption. This process favored the ascent of a different magma in the central conduits, which began to be erupted on 24 September without any significant change in eruptive style, deformation, and seismicity until the end of eruption.     

Geomagnetic Variations Observed on the Earth’s Surface and Associated with Strong Earthquakes

Izvestiya, Physics of the Solid Earth - Abstract—The intensification of geomagnetic variations due to a number of strong remote earthquakes is studied using a chain of ground-based...     

Reply to the Comment by V.A. Saltykov on the Paper “The Relationship between Multifractal and Entropy Properties of Seismic Noise in Kamchatka and Irregularity of the Earth’s Rotation” by A.A. Lyubushin,G.N. Kopylova,and Yu.K. Serafimova

Izvestiya, Physics of the Solid Earth -     

The State of the Art in Studying the Deep Structure of the Earth’s Crust and Upper Mantle beneath the Baikal Rift from Seismological Data

Izvestiya, Physics of the Solid Earth - Abstract—This review discusses the major milestone results yielded by the regional seismological studies of the deep structure of the Earth’s...     

Glaciers in the Earth’s Hydrological Cycle: Assessments of Glacier Mass and Runoff Changes on Global and Regional Scales

Changes in mass contained by mountain glaciers and ice caps can modify the Earth’s hydrological cycle on multiple scales. On a global scale, the mass loss from glaciers contributes to sea-level rise. On regional and local scales, glacier meltwater is an important contributor to and modulator of river flow. In light of strongly accelerated worldwide glacier retreat, the associated glacier mass losses raise concerns over the sustainability of water supplies in many parts of the world. Here, we review recent attempts to quantify glacier mass changes and their effect on river runoff on regional and global scales. We find that glacier runoff is defined ambiguously in the literature, hampering direct comparison of findings on the importance of glacier contribution to runoff. Despite consensus on the hydrological implications to be expected from projected future warming, there is a pressing need for quantifying the associated regional-scale changes in glacier runoff and responses in different climate regimes.     

Spatiotemporal Variations in Gutenberg–Richter b-Value Depending on the Depth and Lateral Position in the Earth’s Crust of the Garm Region,Tajikistan

Izvestiya, Physics of the Solid Earth - Spatiotemporal variations in the Gutenberg–Richter (GR) b-value and in the minimum magnitude of a predicted earthquake (MPE) are studied in detail...     

On mechanical Q parameters of the lower mantle inferred from data on the Earth’s free oscillations and nutation

A new method for the interpretation of recent tidal and astrometry data based on integral relations connecting the mantle Q parameters to variations in frequencies of the main Earth’s spheroidal oscillation, nearly diurnal free nutation, Chandler wobble, and Love numbers is proposed in this paper. The normalized weighting functions in the aforementioned integral relations are shown to be very close to each other in a wide range of oscillation periods (from 54 minutes to 14 months) for the actual Earth’s model and therefore the detection of the dependence of the mantle Q parameters averaged with these weighting functions on frequency does not need to be solved for the inverse problem of the Q parameters as a function of the oscillation frequency and depth: instead, it is sufficient to determine the dependence of the adequate integral characteristics of the mantle’s inelasticity only on frequency. This makes it possible to significantly simplify the solution of the inverse problem and improve the rheologic models of the lower mantle.     

Evidence of multiple strain fields beneath the eastern flank of Mt. Etna volcano (Sicily,Italy) deduced from seismic and geodetic data during 2003–2004

We carried out a study of the seismicity and ground deformation occurring on Mt. Etna volcano after the end of the 2002–2003 eruption and before the onset of the 2004–2005 eruption. Data were recorded by the permanent local seismic network run by Istituto Nazionale di Geofisica e Vulcanologia – Sezione di Catania and by geodetic surveys carried out in July 2003 and July 2004 on the GPS network. Most earthquakes were grouped in two main clusters located in the northeastern and southeastern sectors of the volcano. The areal distribution of seismic energy associated with the recorded earthquakes allowed us to highlight the main seismogenic areas of Mt. Etna. In order to better understand the kinematic processes of the volcano, 3D seismic locations were used to compute fault plane solutions, and a selected dataset was inverted to determine stress and strain tensors. The focal mechanisms in the northeastern sector show clear left-lateral kinematics along an E-W fault plane, consistent with events occurring along the Pernicana Fault system. The fault plane solutions in the southeastern sector show mainly right-lateral kinematics along a NNE and ENE fault plane and left lateral-kinematics along NW fault planes that together suggest roughly E-W oriented compression. Surface ground deformation affecting Mt. Etna measured by GPS surveys highlighted a marked inflation during the same period and exceptionally strong seawards motion of its eastern flank. The 2D geodetic strain tensor distribution was calculated and the results show mainly ENE-WSW extension coupled with WNW-ESE contraction, indicating right-lateral shear along a NW-SE oriented fault plane. The different deformation of the eastern sector of the volcano, as measured by seismicity and ground deformation, must be interpreted by considering the different depths of the two signals. Seismic activity in the southeastern sector of volcano is located between 3 and 8 km b.s.l. and can be associated with a very strong additional E-W compression induced by a pressurizing source just westwards and at the same depth, located by inverting GPS data. Ground deformation, in contrast, is mainly affected by the shallower dynamics of the fast moving eastern flank which produces a shallower opposing E-W extension. The entire dataset shows that two different processes affect the eastern flank at the same time but at different depths; the boundary is clearly located at a depth of 3 km b.s.l. and could represent the décollement surface for the mobile flank.     

Correctives to the scheme of the Earth’s structure inferred from new data on nutation,tides, and free oscillations

When analyzing the new high-accuracy observations of the forced nutation and tidal variations in the acceleration of gravity, it was found that they are in sharp contradiction to the present-day models of the Earth’s interior based on seismic data and the data on the periods and damping constants of the free oscillations of the Earth. The elimination of these contradictions requires analyzing the uniqueness of the interpretation of the free oscillations of the Earth, taking into account the new data.     

New Parameter for Analysis of Ionospheric Disturbances and the Search for Ionospheric Precursors of Earthquakes Based on Barbier’s Formula

Geomagnetism and Aeronomy - A new relative parameter (δBarbier) is proposed for the analysis of ionospheric disturbances and the search for ionospheric precursors of earthquakes. The parameter...