Abstract: The study of crustal and lithospheric thicknesses provides valuable information about the Earth’s dynamics, allowing to identify stress patterns, isostatic compensation degrees and to generate crustal evolution models. Lithospheric thickness in South America is poorly understood, being the Andean region the most studied. The aim of this work is to evaluate the lithospheric structure of the Pantanal basin analyzing S-wave velocity models obtained from the fundamental and higher modes of surface wave from regional earthquakes recorded at the Brazilian Seismic Network Stations (BRASIS). Surface wave group velocity curves were obtained by a multiple filter technique and the classical two-station method was applied to get the fundamental and higher mode phase velocity curves. Inversions of these curves were carried out to obtain the velocity profile for the lithospheric region. This new models reach depths up to 150 km enhancing the lithospheric structure knowledge. This work represents the first analysis of phase velocity using higher modes for the Pantanal basin.
Slidecast:
https://vimeo.com/276918626
Abstract: We describe a first principles methodology to evaluate statistically the hazard related to non-stationary seismic sources like induced seismicity. We use time-dependent Gutenberg-Richter parameters, which leads to a time-varying rate of earthquakes. This is achieved by deriving analytic expressions for occurrence rates which are verified using Monte Carlo simulations. We show two examples: (1) a synthetic case with two seismic sources (background and induced seismicity); and (2) a recent case of induced seismicity, the Horn River Basin, Northeast British Columbia. In both cases, the statistics from the Monte Carlo simulations agree with the analytical quantities. The results show that induced seismicity can change seismic hazard rates but that this greatly depends on both the duration and intensity of the non-stationary sequence as well as the chosen evaluation period. Further studies will include extensions to handle spatial source distributions as well as ground motion analysis in order to generate a complete methodology for non-stationary probabilistic seismic hazard analysis.
Slidecast:
https://vimeo.com/276918374
Abstract: Indonesia is one of the most earthquake disaster-prone countries in the world due to its tectonic activity and high population exposure. To assist with the earthquake response process, Indonesia’s Agency of Meteorology, Climatology and Geophysics (BMKG) generates near-real-time maps of ground motion and shaking intensity (i.e. ShakeMaps) following significant earthquakes. The original ShakeMaps are based on empirical predictions using basic hypocentre and magnitude information, and are generally generated within 5 minutes of the earthquake’s origin. Such maps are updated automatically by incorporating recorded ground motion data from Indonesia’s national Strong-Motion Network. This network, operated and maintained by BMKG, currently includes 278 strong-motion stations, and in 2017 has recorded more than 5000 records from 620 events. The ShakeMap products are subsequently used by Indonesian National Board for Disaster Management (BNPB) to produce near-real time earthquake impact maps in terms of the population exposed to different levels of ground shaking as well as expected number of fatalities. In this paper, we describe the implementation of real-time earthquake impact alerting systems within BMKG and BNPB. We also demonstrate the use of these systems in response to the recent MW 6.5 Kota-Banda Aceh earthquake that occurred on the 7th of December 2016 at a depth of 15 km. The earthquake was reported to have caused 104 fatalities and ~8000 number of displaced people. The integrated ShakeMap system automatically generated shaking estimates calibrated by BMKG’s strong-motion network within 10 minutes of the event’s origin time. The BMKG Shakemaps are automatically uploaded to the InaSAFE Realtime platform, managed by BNPB, to estimate the number of people exposed. It has been observed that recorded ground motions as well as number of casualties are generally consistent with theoretical models.
Slidecast:
https://vimeo.com/276918887
Abstract: Monitor of spatial distribution of ground shaking, that is shake-map, is important for rapid assessment of earthquake damage. Shake-maps usually indicate distribution of eventual distribution of ground shaking (PGA, PGV or seismic intensity), and it does not contain information of time evolution of ground shaking. Here we propose to extend it to shake-map of ongoing ground shaking (hereinafter “shake-map movie”) which gives us time-trace of ground shaking at locations where seismometers do not exist. Real-time application of the shake-map movie enables us to envision distribution of the ground shaking of near future. In this context, shake-map movie is a powerful tool for earthquake early warning. Data assimilation is a technique for precise estimation of the present condition, and it is widely used in meteorology and oceanography in geophysics. We apply the data assimilation technique to estimate the real-time shake-map movie, in which simulation of seismic wave propagation is incorporated into the actual monitor of the shaking. In the data assimilation technique, not only present data, but also all past data are used to estimate the present distribution of ground shaking. The incorporation of past data leads to more precise estimation, as compare with just drawing the contour of present distribution. For application to actual observation, frequency-dependent site amplification factors should be corrected. For the correction of the site amplification in real-time, IIR filters are created which are consistent with the frequency dependence and applicable in time domain. In this presentation, we will show examples of the shake-map movie by applying it to the 2011 Tohoku earthquake (Mw9.0), the 2016 Kumamoto earthquake (Mw7.1), and the 2015 Bonin Islands earthquake (Mw7.9; focal depth 683km).
Slidecast:
Abstract: Previous attempts at imaging the upper mantle intrinsic attenuation structure beneath the southern Sierra Nevada have strongly indicated that propagative effects on t* measurements predominate over anelastic ones. Teleseismic shear wave t* measurements from a handful of events at stations proximal to the Isabella anomaly, a high velocity upper mantle feature, exhibit higher t* values (and therefore higher attenuation) than stations to the east residing in the Basin and Range province, where slower velocities and higher temperature are observed. These results suggest that multipathing and/or defocusing effects on shear-wave amplitudes occur for rays that travel through the high velocity material precluding any straightforward attempts at constraining anelastic attenuation. We explore the spatial extent and azimuthal dependence of multipathing/defocusing effects on t* measurements within the Sierra Nevada using teleseismic S- and SKS- phases recorded by the Sierra Nevada Earthscope Project (SNEP) and the Sierran Paradox Experiment (SPE) seismic networks. However, we also investigate the directional dependence of shear wave amplitude spectra by first accounting for seismic anisotropy in our measurements. Waveforms are first rotated into the Sierran SKSFast, N75°E, and SKSSlow, N15°W, direction. Following the method of Stachnik et al., (2004), shear-wave spectra for each event are jointly inverted for a single seismic moment, M0k, and corner frequency, fck, and separate t* for each ray path. Defocusing and anelastic effects on t* measurements are modeled using E3D, an elastic finite-difference wave propagation code that can incorporate attenuation. Defocusing effects are modeled using simple high-velocity geometries including a spherical “drip” and a tabular, east-plunging structure.
Slidecast:
https://vimeo.com/276930227
Abstract: General ray theory recently developed for P and S body waves in layered viscoelastic media provides new insights for the travel-time and amplitude-attenuation characteristics of seismic waves in an anelastic Earth. Solutions of the forward ray tracing problems for horizontal and spherical media account for changes in velocity and attenuation of general P and S waves, which are due to changes in wave inhomogeneity induced by contrasts in intrinsic anelastic material parameters encountered by anelastic rays. These changes, which may manifest themselves as measurable variations in travel-time and amplitude-attenuation as observed at the surface, are not predicted by elastic models. In addition, viscoelastic solutions for general head waves provide a plane-wave explanation for seismic head-wave arrivals, in that the refracted anelastic solution may carry significant components of energy parallel and away from the boundary and result in ray paths reflected from deeper boundaries that are not predicted by elastic models. Solutions of inverse problems to infer the intrinsic material absorption and wave speed of anelastic Earth materials are developed to account for changes in measured travel-time and amplitude-attenuation curves due to changes in inhomogeneity of the waves along an anelastic ray path. Generalizations of the Herglotz-Wiechert integral solution from elastic to viscoelastic media are developed as an essential step in the solution of the inverse problem for anelastic horizontal and spherical media with gradients in intrinsic material absorption. These insights will be discussed in the context of the mathematical framework for general viscoelastic ray theory.
Slidecast:
https://vimeo.com/276926934
