Elastic wave extrapolation in the time domain is significant for an elastic wave equation-based processing. To improve the simulation reliability and accuracy of decoupled elastic P- and S- waves, we propose the staggered-grid lowrank finite-difference method based on the elastic wave decomposition. For elastic wave propagation, a lowrank finite-difference method based on the staggered grid is derived to improve the accuracy. Regarding the application of the decoupled elastic wave equation, we derive the finite-difference scheme coefficients which are dependent on velocity. Based on the elastic wave decomposition and plane wave theories, we formulate the elastic wave-extrapolation operators, which contain trigonometric adjustment factors. Accordingly, by applying the lowrank method to approximating the operators, the finite- difference scheme is designed to discretize the decoupled wave equation. The derivation processing implies the combination of elastic wave-mode decomposition and extrapolation. The proposed method enables elastic P- and S-waves to extrapolate in the time-space domain separately and produces accurate P-and S-wave components simultaneously. Dispersion analysis suggests that our proposed method is reliable and accurate in a wide range of wavenumber. Numerical simulation tests on a simple model and the Marmousi2 model validate the accuracy and effectiveness of the method, showing its ability in handling complex structures. Although the operators are accurate only when the medium is homogeneous, they are of high accuracy when the velocity gradient is quite small and are applicable when the velocity gradient is large. The subsequent results of reverse time migration for the Marmousi2 model also suggest that the proposed method is enough to serve as an extrapolator in elastic reverse time migration.

This study is focused on the inertial effect on slip of and interaction between two earthquake faults based on a two-body slider-slider model in the presence of thermal-pressurized slip-weakening friction and viscosity. The ratio m=m2/m1, where m2 and m1 are the masses of sliders 1 and 2, respectively, is the model parameter to represent the inertial effect. Other model parameters are s (the stiffness ratio), f= fo2/fo1 (where foi is the normalized static friction force on the i-th slider, i=1, 2), y=Uc2/Uc1 (where Uci is the normalized characteristic displacement of friction law on the i-th slider), and g=h2/h1 (where hi is the normalized viscosity coefficient between the i-th slider and the background plate). Simulation results show that m is important on interaction between the two sliders. Foreshocks and aftershocks/afterslip can be generated on slider 1 or slider 2 when m≠1. Slider 2 behaves like a slow event when m≥50. The f, y, and g are the major factors and s is minor one in causing time delay between the two sliders. Slider 2 cannot move when f is higher than a critical value which depends on other model parameters. Interaction and the patterns of motions of the two sliders are different between y<1 and y>1. The presence of viscosity may increase the predominant period of a slider.

This paper investigates the characteristic of the ionospheric delay and forecasting using modified statistical Holt-Winter method over Malaysia. This was carried out by using dual frequency GPS Ionospheric Scintillation and TEC Monitor (GISTM) receivers installed at the National University of Malaysia (UKM) (geographic coordinates 2.55°N, 101.46°E and geomagnetic coordinates 7.10°S, 174.05°E), and Langkawi national observatory (Langkawi) (geographical coordinates 6.19°N, 99.51°E and geomagnetic coordinates 3.39°S, 172.42°E), during 2011. In this work, the Holt-Winter forecasting method is modified to provide a better forecasting result over Malaysia. The diurnal, monthly, and seasonal variations of actual ionospheric delay have been analyzed and compared with forecasted ionospheric delay. Based on the results, the diurnal variability of ionospheric delay was maximal mostly between 12:00– 17:00 LT, and minimal nearly at 05:00 LT. The maximum monthly ionospheric delays occurred in October, which is attributed to the geomagnetic storm disturbance that caused increase in ionospheric delay. The lowest seasonal ionospheric delay occurred in the summer and the highest was during the equinox. The maximum ionospheric delay on a quiet day was around 41.9 TECU, while it reached up to 86.6 TECU during the geomagnetic storm. The Holt-Winter method exhibited the highest difference between the measurements and the forecasts in March, with an error of 6%. Hence, the modified Holt-Winter method forecast ionospheric delay effectively during quiet and disturbed periods over Malaysia.

The Tectonic stress regime of Gulf of Guinea region has been studied by stress tensor inversion analysis for the area bounded by lati− tude −10.0 0 S to 4.0oN and longitude −25 0 W to −11.0 0 E. A total of one hundred and four focal mechanism solutions, pertaining to the earthquake events which have occurred in this region, were used for this study. In order to decipher the stress pattern of this region, we have divided the region into four fracture zones namely Romanche, Chain−Romanche, Charcot and Ascension fracture−zones based on seismicity clustering, tectonics and available focal mechanism solutions. The seismicity pattern indicates that none of the nearby coun− tries on the border line between the west Africa region and the gulf of Guinea is devoid of seismicity. Simultaneously, the stress tensor inversion in the four subzones of investigation indicates different types of stress orientations. All of these zones are characterized by vary− ing principal axial directions. The orientation of the principal axial direction along Romanche, Chain−Romanche, Charcot and Ascen− sion fracture−zones are along NE−SW, NE−SW, ENE−WSW and ESE−WNW respectively. The stress tensor inversion results indicate that Chain−Romanche, Charcot and Ascension fracture zones are characterized by extensional stress regime while Romanche fracture zone is characterized by strike−slip stress regime respectively. These patterns imply sea floor spreading activities in and around the mid oceanic ridges and the general orientation of the extensional stress regime is found towards the continents, along the line of migration / progression of earthquakes.

Major geomagnetic storms drive rapid intensification and variability of magnetospheric and iono- spheric current systems that give rise to large ground-induced currents (GIC). Space weather as- sociated GIC pose a serious threat to the reliability of power-transmission systems and other elec- trically conducting infrastructure such as oil and gas pipelines. The most severe effects are ob- served at high latitudes due to ionospheric currents associated with the aurora. However, as power transmission grid and pipeline infrastructure continues to grow at middle and low-latitudes, GIC hazards are no longer just concerns of high-latitude regions. We investigate how GIC amplitude varies in latitude during six major geomagnetic storms that occurred between 1989 and 2004. Due to limited direct GIC measurements, a proxy of the geoelectric field is used, i.e. the GIC index. This is calculated for the selected geomagnetic storms using 25 magnetic observatories relatively uniformly distributed in geomagnetic latitude, 14 magnetic observatories with longitudes varying within a range of 45 degrees as well as for the 7 November 2004 storm using 104 observatories. In addition, we suggest a possible way to follow the latitudinal displacement of the auroral oval dur- ing geomagnetic storms through the maximum value of GIC index, estimated over 2-hour inter- vals on a wide number of magnetic observatories.

Turkey has confronted numerous severe and destructive earthquakes for centuries because of being located on the Mediterranean Seismic Belt. Proven to be safe due to their lightness and ductile nature, wooden buildings have gained importance in the course of time in this land. In this paper, earthquake−resistant timber constructions and the use of wooden material as an absorbing element for seismic forces in Anatolia and Thrace are investigated based on the historical development process with the help of the archaeological data. The seismic structure, forests and timber residential placements of Turkey are studied in relation with each other at first. Accordingly the sustainable development process of architectural plan types and structural systems that are able to withstand earthquakes were mentioned under the light of archaeological findings. The structural characteristics that render a traditional timber building earthquake−resistant were researched according to the regional distribution, material and structural features and the most advanced structural systems used in both timber and timber−masonry composite systems were demonstrated as living examples today.

The emergency planning of areas subjected to volcanic risk requires the evaluation of impact induced on different element exposed (people, buildings, infrastructures, economy, etc.) by different volcanic phenomena (precursor earthquakes, ash fall, pyroclastic flows, lahars, tsunami, ballistics, landslides, etc.). In this paper, the authors describe the methodology developed at PLINIVS Study Centre (University of Naples Federico II, Italy), Centre of Competence of the Italian Civil Protection, in the framework of volcanic risk concerning the Campania Region volcanoes. The approach is based on the probabilistic analyses of risk and impact scenarios. It allows quantifying the potential losses consequent to possible volcanic eruptions. The results are strongly dependent on the hypothesis assumed and on the parameters used as inputs, providing impact scenarios with a probabilistic estimation and uncertainty treatment. The results constitute an useful tool for emergency planners and decision makers in the evaluation of the resources needed to improve the preparedness measures and to implement at technically feasible and cost-effective mitigation measures on buildings and infrastructure. The scope is to reduce the expected damage, such as the seismic retrofitting of vulnerable buildings along the escape routes identified in the evacuation plan, which might fail due to the presence of debris from collapsed buildings which can affect the practicability of roads. The paper is focussed on the relevant applications performed by PLINIVS simulation model for the preparation and updating of the emergency plan for Vesuvius and Campi Flegrei areas.

The development of new bi- and tri-dimensional (2D, 3D) analytical techniques of volcanic materials represents a new frontier in the world of modern volcanology. These advances not only offer important and reliable information on, e.g., magma vesiculation, degassing, and crystallization processes but can also shade light on the transport and sedimentation processes in volcanic flows (e.g. pyroclastic density currents, volcanic clouds). Hence, these novel approaches have the potential to contribute both to the understanding eruption dynamics towards volcanic hazard quantification.

New Zealand earthquake that occurred on 15th July 2009 (Mw 7.8) was analysed using fractal correlation dimension (Dc) and seismic b-VALUE. We have analysed the earthquakes catalog of thirty- ve years with a magnitude (mb ≥3.7), in order to observe a crucial in- formation in terms of Dc value uctuation for the event. The event is preceded by fall and anomalous change in Dc value in the year 2007 about two years prior to the mainshock. A sudden decrease in Dc value with highly clustered events is observed before the main- shock. The low value of Dc is an indicator of clustering and it shows how intermediate size events correlate with one another in the pre- paration process of this event. Here the low Dc value may be the indicator for high stress developer along the fault to produce large size earthquake. Moreover, we also observed abnormal uctuation in b-VALUE from 2003. The fractal clustering and scaling of earthquakes are indicated by b-VALUE change prior to strong earthquake as a harbinger of stress correlation in various scales. The event is also mar- ked for that occurred in the periphery of the positive Coulomb stress development, as obtained from three low Dc time windows' events. The drop in Dc value is not a single observation prior to this large event, but such pattern is also seen for other strong events in the study zone. One such well identi ed strong event is Mw 7.2 (2003) along with low Dc value prior to the event. Thus, stress correlation mea- sured along with these indirect statistical tools gives the clue of self-organization of long wavelength of stress, which was not measu- red earlier with classical approaches. This type of study may provide a very useful information for hazard mitigation.

Propagation of a lava flow is governed by slope topography, magma rheology, heat exchange with the atmosphere and the underlying terrain, and the rate of the eruption. Highly viscous crust is formed due to cooling and solidification of the uppermost layer of the flow. We consider here two numerical model problems for lava flows, both based on the fundamental physics of a hot fluid flow: a model problem, where thermal conditions (e.g. temperature and heat flow) at the lava surface are unknown a priori (a direct model problem), and a model problem, where the lava surface conditions are known and determined from observations(an inverse model problem). In both models, the lava viscosity depends on temperature and the volume fraction of crystals. By way of solving the direct model problem, we perform a parametric study of steady state lava flows to investigate the influence of the heat flux, viscosity, and effusion rate on the lava crust development. Numerical experiments show that a lava crust becomes thicker in the case of the nonlinear heat transfer compared to the case of a linear heat flow at the interface of lava with the atmosphere. Also, the crust thickens at lower lava effusion rates, while higher rates result in a rapid lava advection, slower cooling, and development of a thinner crust. Moreover, a lava crust becomes thicker with a higher coefficient of conductive heat transfer, or a higher lava viscosity, or the growth of effective emissivity of the lava surface. By way of solving the inverse model problem, we use an assimilation technique (that is, a method for an optimal combination of a numerical model of lava flows with observations) to propagate the temperature and heat flow, inferred from measurements at the interface between lava and the atmosphere, into the lava flow interior and to analyse the evolving lava crust. Results of thermal data assimilation illustrate that the physical parameters of lava flows, including the thickness of it crust, can be recovered from measured surface thermal data well enough at least for slow effusion rates.