Preprints
Filtering by Subject: Geophysics and Seismology
Seismic and structural characterization of a pre-salt rifted section: the Lagoa Feia Group, Campos Basin, offshore Brazil
Published: 2017-11-17
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics, Stratigraphy
The exploration of pre-salt offshore SE Brazil presents a multifaceted deep-water scenario that is bringing new challenges to seismic interpretation in offshore Brazilian exploration and production. Reservoirs in this domain are complex, heterogeneous with layered carbonates which makes accurate reservoir characterization very challenging. Our study here deals with the seismic characterization of [...]
A new global mode of Earth deformation: seasonal cycle detected
Published: 2017-11-13
Subjects: Earth Sciences, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Hydrology, Oceanography and Atmospheric Sciences and Meteorology, Other Earth Sciences, Other Environmental Sciences, Other Oceanography and Atmospheric Sciences and Meteorology, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics
We have detected a global mode of Earth deformation that is predicted by theory. Precise positioning of GPS sites distributed worldwide reveals that in February to March the northern hemisphere compresses (and the southern hemisphere expands), such that sites near the North Pole move downward by 3.0 mm, and sites near the equator are pulled northwards by 1.5 mm. The opposite pattern of [...]
Choice of optimal averaging radii for temporal GRACE gravity solutions, a comparison with GPS and satellite altimetry
Published: 2017-11-13
Subjects: Earth Sciences, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Glaciology, Hydrology, Other Earth Sciences, Other Environmental Sciences, Physical Sciences and Mathematics
One of the initial challenges of the GRACE mission is to validate the accuracy of the time-variable gravity fields. These gravity fields contain both spatially correlated (systematic) and random noise and hence spatial averaging needs to be implemented. Before the fields may be interpreted, optimum averaging radii need to be determined through comparison with independent data. We compare time [...]
A comparison of GPS, VLBI and model estimates of ocean tide loading displacements
Published: 2017-11-13
Subjects: Civil and Environmental Engineering, Earth Sciences, Engineering, Environmental Sciences, Geophysics and Seismology, Other Civil and Environmental Engineering, Other Earth Sciences, Physical Sciences and Mathematics
In recent years, Ocean Tide Loading Displacements (OTLD) have been measured using the Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI). This study assesses the accuracy of GPS measurements of OTLD by comparison with VLBI measurements and estimates derived from numerical ocean tide models. A daily precise point positioning (PPP) analysis was carried out on ~11 years of [...]
Basis functions for the consistent and accurate representation of surface mass loading
Published: 2017-11-13
Subjects: Applied Mathematics, Earth Sciences, Environmental Indicators and Impact Assessment, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Numerical Analysis and Computation, Oceanography and Atmospheric Sciences and Meteorology, Other Earth Sciences, Other Environmental Sciences, Other Oceanography and Atmospheric Sciences and Meteorology, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics
Inversion of geodetic site displacement data to infer surface mass loads has previously been demonstrated using a spherical harmonic representation of the load. This method suffers from the continent-rich, ocean-poor distribution of the geodetic data, coupled with the predominance of the continental load (water storage and atmospheric pressure) compared with the ocean bottom pressure (including [...]
Using filtered and semi-continuous high rate GPS for monitoring deformations
Published: 2017-11-13
Subjects: Civil and Environmental Engineering, Civil Engineering, Construction Engineering and Management, Earth Sciences, Engineering, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Geotechnical Engineering, Other Civil and Environmental Engineering, Other Earth Sciences, Other Environmental Sciences, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics, Structural Engineering
Multipath is a major sidereally-repeating error affecting precise GPS positioning and deformation monitoring. Because satellite-receiver geometry repeats almost exactly every sidereal day, filtering can reduce multipath in near-static situations. Here, we investigate how sidereal filtering can be used in a switched multi-antenna array system providing semi-continuous GPS data, which may be [...]
J2: an evaluation of new estimates from GPS, GRACE and load models compared to SLR
Published: 2017-11-13
Subjects: Earth Sciences, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Other Earth Sciences, Other Environmental Sciences, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics
Changes in J2, resulting from past and present changes in Earth’s climate, are traditionally observed by Satellite Laser ranging (SLR). Assuming an elastic Earth, it is possible to infer changes in J2 from changes in Earth’s shape observed by GPS. We compare estimates of non-secular J2 changes from GPS, SLR, GRACE and a load model. The GPS and SLR annual signals agree but are different (16%) to [...]
An examination of network RTK GPS services in Great Britain
Published: 2017-11-13
Subjects: Civil and Environmental Engineering, Civil Engineering, Construction Engineering and Management, Earth Sciences, Engineering, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Other Civil and Environmental Engineering, Other Earth Sciences, Other Environmental Sciences, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics
As of March 2009, network real-time kinematic (RTK) GPS surveying is available in Great Britain with the aid of two commercial service providers, Leica’s “SmartNet” and Trimble’s “VRS Now”, both of which rely largely on the Ordnance Survey’s “OS Net” network of around 120 continuously operating reference stations. With the aim of testing the performance of Network RTK under both ideal and [...]
Ocean tide loading and relative GNSS in the British Isles
Published: 2017-11-13
Subjects: Civil and Environmental Engineering, Earth Sciences, Engineering, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Oceanography and Atmospheric Sciences and Meteorology, Other Civil and Environmental Engineering, Other Earth Sciences, Other Environmental Sciences, Other Oceanography and Atmospheric Sciences and Meteorology, Other Physical Sciences and Mathematics, Physical Sciences and Mathematics
Ocean tide loading (OTL) affects all parts of the British Isles to varying degree, causing peak-to-peak vertical displacements of up to 13 cm in South-West England over semi-diurnal and diurnal timescales. Lateral displacements are typically around one-third of the magnitude of vertical displacements at a point, so are also considerable for carrier phase GNSS surveying. Using a recent numerical [...]
Increased ice loading in the Antarctic Peninsula since the 1850s and its effect on Glacial Isostatic Adjustment
Published: 2017-11-13
Subjects: Climate, Earth Sciences, Environmental Monitoring, Environmental Sciences, Geophysics and Seismology, Glaciology, Oceanography and Atmospheric Sciences and Meteorology, Other Earth Sciences, Other Environmental Sciences, Physical Sciences and Mathematics
Antarctic Peninsula (AP) ice core records indicate significant accumulation increase since 1855, and any resultant ice mass increase has the potential to contribute substantially to present-day Glacial Isostatic Adjustment (GIA). We derive empirical orthogonal functions from climate model output to infer typical spatial patterns of accumulation over the AP and, by combining with ice core records, [...]
Computationally Efficient Tsunami Modelling on Graphics Processing Units (GPU)
Published: 2017-11-13
Subjects: Applied Mathematics, Civil and Environmental Engineering, Civil Engineering, Computer Sciences, Earth Sciences, Engineering, Environmental Sciences, Geophysics and Seismology, Hydraulic Engineering, Numerical Analysis and Computation, Numerical Analysis and Scientific Computing, Other Civil and Environmental Engineering, Other Earth Sciences, Other Environmental Sciences, Physical Sciences and Mathematics
Tsunamis generated by earthquakes commonly propagate as long waves in the deep ocean and develop into sharp-fronted surges moving rapidly towards the coast in shallow water, which may be effectively simulated by hydrodynamic models solving the nonlinear shallow water equations (SWEs). However, most of the existing tsunami models suffer from long simulation time for large-scale real-world [...]
Ratio-to-moving-average seismograms: a strategy for improving correlation detector performance
Published: 2017-11-09
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
Correlation detectors are becoming a standard method for identifying seismic signals from repeating sources. These highly sensitive, source-specific detectors frequently facilitate a reduction in the detection threshold by around an order of magnitude. Detections are typically declared when the value of the correlation coefficient (CC), or a related statistic, exceeds significantly some measure [...]
Improvements to Seismic Monitoring of the European Arctic Using Three-Component Array Processing at SPITS
Published: 2017-11-09
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
The detectability of low magnitude seismic events in the European Arctic is determined primarily by the small-aperture International Monitoring System arrays ARCES and SPITS. In August 2004, the SPITS array was upgraded to a broadband array with an increase in the sampling rate from 40 to 80 Hz. Most important, however, for the detection and location of small-magnitude seismic events was the [...]
Seismic Monitoring of the North Korea Nuclear Test Site Using a Multichannel Correlation Detector
Published: 2017-11-09
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
North Korea announced a second nuclear test on 25 May 2009, the first having taken place on October 9, 2006. Both tests were detected by the global seismic network of the Comprehensive nuclear Test-Ban-Treaty Organisation. We apply a correlation detector using a 10-s signal template from the 2006 test on the MJAR array in Japan to: 1) assess the potential for automatically detecting subsequent [...]
The detection of low magnitude seismic events using array-based waveform correlation
Published: 2017-11-08
Subjects: Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics
It has long been accepted that occurrences of a known signal are most effectively detected by cross-correlating the incoming data stream with a waveform template. Such matched signal detectors have received very little attention in the field of detection seismology because there are relatively few instances in which the form of an anticipated seismic signal is known a priori. Repeating events in [...]