Stochastic Strong Ground Motion Simulation of the Southern Aegean Sea Benioff Zone Intermediate‐Depth Earthquakes

2018 ◽  
Vol 108 (2) ◽  
pp. 946-965 ◽  
Author(s):  
Ch. Kkallas ◽  
C. B. Papazachos ◽  
B. N. Margaris ◽  
D. Boore ◽  
Ch. Ventouzi ◽  
...  
Keyword(s):  
Aegean Sea ◽  
Benioff Zone ◽  
Model Parameters ◽  
Waveform Data ◽  
Intermediate Depth ◽  
Stress Parameter ◽  
Finite Fault ◽  
Strong Ground Motion Simulation ◽  
Back Arc ◽  
Parameter Values

Abstract We employ the stochastic finite‐fault modeling approach of Motazedian and Atkinson (2005), as adapted by Boore (2009), for the simulation of Fourier amplitude spectra (FAS) of intermediate‐depth earthquakes in the southern Aegean Sea subduction (southern Greece). To calibrate the necessary model parameters of the stochastic finite‐fault method, we used waveform data from both acceleration and broadband‐velocity sensor instruments for intermediate‐depth earthquakes (depths ∼45–140  km) with M 4.5–6.7 that occurred along the southern Aegean Sea Wadati–Benioff zone. The anelastic attenuation parameters employed for the simulations were adapted from recent studies, suggesting large back‐arc to fore‐arc attenuation differences. High‐frequency spectral slopes (kappa values) were constrained from the analysis of a large number of earthquakes from the high‐density EGELADOS (Exploring the Geodynamics of Subducted Lithosphere Using an Amphibian Deployment of Seismographs) temporary network. Because of the lack of site‐specific information, generic site amplification functions available for the Aegean Sea region were adopted. Using the previous source, path, and site‐effect constraints, we solved for the stress‐parameter values by a trial‐and‐error approach, in an attempt to fit the FAS of the available intermediate‐depth earthquake waveforms. Despite the fact that most source, path, and site model parameters are based on independent studies and a single source parameter (stress parameter) is optimized, an excellent comparison between observations and simulations is found for both peak ground acceleration (PGA) and peak ground velocity (PGV), as well as for FAS values. The final stress‐parameter values increase with moment magnitude, reaching large values (>300  bars) for events M≥6.0. Blind tests for an event not used for the model calibration verify the good agreement of the simulated and observed ground motions for both back‐arc and along‐arc stations. The results suggest that the employed approach can be efficiently used for the modeling of large historical intermediate‐depth earthquakes, as well as for seismic hazard assessment for similar intermediate‐depth events in the southern Aegean Sea area.

Investigation of the stress parameter values for the stochastic simulation of shallow (h<45km) interface earthquakes of the southern Aegean Sea subduction zone

2021 ◽  
Author(s):  
Charalampos Kkallas ◽  
Constantinos Papazachos ◽  
Basil Margaris ◽  
Ioannis Grendas ◽  
Nikos Theodoulidis ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Stochastic Simulation ◽  
Transfer Functions ◽  
Strong Motion ◽  
Aegean Sea ◽  
Extended Source ◽  
Stress Parameter ◽  
Parametric Search ◽  
Parameter Values ◽  
Stress Parameters

&lt;p&gt;In the present work, we examine the stress parameter values for the stochastic simulation modeling of shallow interface (h&lt;45km) earthquakes in the southern Aegean Sea subduction zone. Using the extended-source model (EXSIM code), the stochastic stress parameter is estimated for several of these earthquakes, which are typically associated with thrust faulting. The assessment is performed using a Monte Carlo parametric search (non-linear optimization) of the stress parameter values, realized through an adapted neighborhood algorithm (Wathelet, 2008). In this approach, we estimate the stress parameter which minimizes the total root mean square (rms) misfit between observed and simulated Fourier Amplitude Spectra (FAS) for all records of each event available in the strong motion database. We also employ appropriate source and path parameters (e.g., moment magnitude, fault dimensions, high-frequency spectral attenuation, etc.), from previous works on strong-motion simulations, considering earthquakes in the range &lt;strong&gt;M&lt;/strong&gt;4.4 to &lt;strong&gt;M&lt;/strong&gt;6.6. For several recording stations, we employed site-specific transfer functions, derived from a generalized inversion of strong motion records, considering the seismic source and propagation path of the seismic events in terms of their frequency content (Drouet et al., 2008; Grendas et al., 2018). For the remaining stations, the assessment of site-effects on seismic motions was performed based on the Vs30 values available for all recording stations. Using these values, soil classes according to NEHRP (1994) have been assigned and we employed generic transfer functions for NEHRP site conditions A/B, C and D (together with the corresponding &amp;#954;0 values), as these were available from previous work for Greece by several authors (Margaris and Boore, 1998, Margaris and Hatzidimitriou, 2002; Klimis et al., 1999, 2006). The final comparisons show that the FAS of the strong motion data can be adequately matched (in most cases) by the synthetic data from the EXSIM simulations, using stress parameter values less than 100bars. This value is quite different from results obtained for larger depth interface and inslab events of the Aegean Sea and Vrancea subduction zones (e.g., Sokolov et al., 2005; Kkallas et al., 2018), which show much larger stress parameters (&gt;200bar) for &lt;strong&gt;M&lt;/strong&gt;&gt;6 events. These findings suggest that the event hypocentral depth is a critical factor regarding the observed stress parameter affecting accordingly the seismic hazard estimation. Strong Intermediate-depth events (h&gt;45km) require large stress parameters, while shallow interface thrust events show rather similar stress parameter values with the typical shallow back-arc normal and strike-slip events of the Aegean region. &lt;strong&gt;This research is co-financed by Greece and the European Union (European Social Fund- ESF) through &lt;/strong&gt;&lt;strong&gt;the Operational Programme &amp;#171;Human Resources Development, Education and Lifelong Learning&amp;#187; in &lt;/strong&gt;&lt;strong&gt;the context of the project &amp;#8220;Reinforcement of Postdoctoral Researchers - 2&lt;/strong&gt;&lt;strong&gt;nd &lt;/strong&gt;&lt;strong&gt;Cycle&amp;#8221; (MIS-5033021), &lt;/strong&gt;&lt;strong&gt;implemented by the State Scholarships Foundation (&amp;#921;&amp;#922;&amp;#933;).&lt;/strong&gt;&lt;/p&gt;

scholarly journals Assimilation of Dynamic Combined Finite Discrete Element Methods Using the Ensemble Kalman Filter

2021 ◽  
Vol 11 (7) ◽  
pp. 2898
Author(s):  
Humberto C. Godinez ◽  
Esteban Rougier
Keyword(s):  
Kalman Filter ◽  
Ensemble Kalman Filter ◽  
Failure Modes ◽  
Split Hopkinson Pressure Bar ◽  
Peak Stress ◽  
Discrete Element ◽  
Material Behavior ◽  
Model Parameters ◽  
Hopkinson Pressure Bar ◽  
Parameter Values

Simulation of fracture initiation, propagation, and arrest is a problem of interest for many applications in the scientific community. There are a number of numerical methods used for this purpose, and among the most widely accepted is the combined finite-discrete element method (FDEM). To model fracture with FDEM, material behavior is described by specifying a combination of elastic properties, strengths (in the normal and tangential directions), and energy dissipated in failure modes I and II, which are modeled by incorporating a parameterized softening curve defining a post-peak stress-displacement relationship unique to each material. In this work, we implement a data assimilation method to estimate key model parameter values with the objective of improving the calibration processes for FDEM fracture simulations. Specifically, we implement the ensemble Kalman filter assimilation method to the Hybrid Optimization Software Suite (HOSS), a FDEM-based code which was developed for the simulation of fracture and fragmentation behavior. We present a set of assimilation experiments to match the numerical results obtained for a Split Hopkinson Pressure Bar (SHPB) model with experimental observations for granite. We achieved this by calibrating a subset of model parameters. The results show a steady convergence of the assimilated parameter values towards observed time/stress curves from the SHPB observations. In particular, both tensile and shear strengths seem to be converging faster than the other parameters considered.

scholarly journals An enhanced set of displacement parameter restraints in CRYSTALS

2018 ◽  
Vol 51 (4) ◽  
pp. 1059-1068 ◽  
Author(s):  
Pascal Parois ◽  
James Arnold ◽  
Richard Cooper
Keyword(s):  
Structural Model ◽  
Rigid Bodies ◽  
Model Parameters ◽  
Coordinate Systems ◽  
Principal Axes ◽  
Anisotropic Displacement Parameters ◽  
Set Up ◽  
Meaningful Relationships ◽  
Parameter Values ◽  
Total Model

Crystallographic restraints are widely used during refinement of small-molecule and macromolecular crystal structures. They can be especially useful for introducing additional observations and information into structure refinements against low-quality or low-resolution data (e.g. data obtained at high pressure) or to retain physically meaningful parameter values in disordered or unstable refinements. However, despite the fact that the anisotropic displacement parameters (ADPs) often constitute more than half of the total model parameters determined in a structure analysis, there are relatively few useful restraints for them, examples being Hirshfeld rigid-bond restraints, direct equivalence of parameters and SHELXL RIGU-type restraints. Conversely, geometric parameters can be subject to a multitude of restraints (e.g. absolute or relative distance, angle, planarity, chiral volume, and geometric similarity). This article presents a series of new ADP restraints implemented in CRYSTALS [Parois, Cooper & Thompson (2015), Chem. Cent. J. 9, 30] to give more control over ADPs by restraining, in a variety of ways, the directions and magnitudes of the principal axes of the ellipsoids in locally defined coordinate systems. The use of these new ADPs results in more realistic models, as well as a better user experience, through restraints that are more efficient and faster to set up. The use of these restraints is recommended to preserve physically meaningful relationships between displacement parameters in a structural model for rigid bodies, rotationally disordered groups and low-completeness data.

Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event

1990 ◽  
Vol 80 (3) ◽  
pp. 507-518 ◽  
Author(s):  
Jim Mori ◽  
Stephen Hartzell
Keyword(s):  
Green Function ◽  
Fault Plane ◽  
Least Squares Method ◽  
Source Area ◽  
Rupture Velocity ◽  
P Waves ◽  
Waveform Data ◽  
Empirical Green Function ◽  
Finite Fault ◽  
Short Period

Abstract We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4.6) earthquake near Upland, California. We removed path and site complications by choosing a small aftershock (ML 2.7) as an empirical Green function. The main shock P waves were deconvolved by using the empirical Green function to produce simple far-field displacement pulses. We used a least-squares method to invert these pulses for the slip distribution on a finite fault. Both nodal planes (strike 125°, dip 85° and strike 221°, dip 40°) of the first-motion focal mechanism were tested at various rupture velocities. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 × 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. Choice of a southwest-trending fault plane is consistent with the trend of the nearby portion of the Transverse Ranges frontal fault zone and indicates left-lateral motion. This method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations.

Source Process-Related Delays in Earthquake Early Warning for Example Cases in Greece

2021 ◽  
Author(s):  
Nikolaos Vavlas ◽  
Anastasia A. Kiratzi ◽  
Zafeiria Roumelioti
Keyword(s):  
Early Warning ◽  
Monitoring Network ◽  
Earthquake Early Warning ◽  
Source Process ◽  
Spatial Density ◽  
Intermediate Depth ◽  
National Monitoring ◽  
Gulf Of Corinth ◽  
Crete Island ◽  
Finite Fault

ABSTRACT We explore a hypothetical zero-latency earthquake early warning (EEW) system in Greece, aiming to provide alerts before warning thresholds of the intensity of ground motion are exceeded. Within the seismotectonic context of Greece, both shallow- and intermediate-depth earthquakes (along the Hellenic subduction zone) are plausible and, thus, examined. Using regionally applicable attenuation relations, we combine and adjust the methodologies of Minson et al. (2018) and Hoshiba (2020) to examine what are the minimum magnitudes required to invoke the warning thresholds at the user site. With simple modeling, we examine how fast an alert can be issued and what is the available warning time when taking into account delays due to finite-fault rupture propagation, alongside other delays. These computations are merged with delays introduced due to the present-day configuration of the Greek national monitoring network (varying spatial density of permanent monitoring stations). This approach serves as a tool to assess the feasibility of an EEW system at specific sites and to redesign the national permanent monitoring network to serve such a system more effectively (we provide results for four sites.). Warning times for on-land crustal earthquakes are found to be shorter, whereas for intermediate-depth earthquakes in Greece an EEW system is feasible (provides warning times of several tens of seconds at large cities, e.g., on Crete Island) even with the current configuration of the national monitoring network, which is quite sparse in the southern part of the country. The current network configuration also provides sufficient early warning (e.g., of the order of 10 s for a warning threshold of 0.05g) at the center of Athens from earthquakes of the eastern Gulf of Corinth—a zone posing elevated hazard in the broader area of the Greek capital. Several additional assumptions and factors affecting the operability of an EEW system in Greece (i.e., source process complexity and uncertainty in attenuation laws) are also discussed.

Deep Structure and Active Tectonics of the South Aegean Volcanic Arc

Elements ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 153-158 ◽  
Author(s):  
Costas B. Papazachos
Keyword(s):  
Deep Structure ◽  
Active Tectonics ◽  
Aegean Sea ◽  
Low Velocity ◽  
Volcanic Arc ◽  
High Attenuation ◽  
Global Positioning ◽  
Back Arc ◽  
The Impact ◽  
Subducting Slab

The seismotectonic setting of the Aegean Sea, based on information from seismicity, neotectonics and global positioning system studies, is characterized by a sharp transition from a compressional outer arc to a complex back-arc, with an approximate north–south extension along the volcanic arc. Seismicity and 3-D tomography studies reveal the geometry of the subducting slab and image the low-velocity/high-attenuation mantle wedge at depths of 50–80 km beneath the volcanic arc where magma is generated. The 1956 Amorgos M7.5 earthquake and the impact from its seismic shaking and landslide-triggered tsunamis are discussed in the context of the regional seismotectonic setting.

scholarly journals Modelling temperature variations in polar snow using DAISY

1997 ◽  
Vol 43 (143) ◽  
pp. 180-191 ◽  
Author(s):  
Ε. M. Morris ◽  
H. -P. Bader ◽  
P. Weilenmann
Keyword(s):  
Field Experiments ◽  
A Priori ◽  
Model Parameters ◽  
Data Set ◽  
International Geophysical Year ◽  
Snow Model ◽  
Using Data ◽  
Polar Snow ◽  
Parameter Values ◽  
The Antarctic

AbstractA physics-based snow model has been calibrated using data collected at Halley Bay, Antarctica, during the International Geophysical Year. Variations in snow temperature and density are well-simulated using values for the model parameters within the range reported from other polar field experiments. The effect of uncertainty in the parameter values on the accuracy of the predictions is no greater than the effect of instrumental error in the input data. Thus, this model can be used with parameters determined a priori rather than by optimization. The model has been validated using an independent data set from Halley Bay and then used to estimate 10 m temperatures on the Antarctic Peninsula plateau over the last half-century.

Torsional damping of a back-to-back gearbox rig: Experimental measurements and frequency domain modelling

2002 ◽  
Vol 216 (2) ◽  
pp. 157-168 ◽  
Author(s):  
S J Drew ◽  
B J Stone
Keyword(s):  
Frequency Domain ◽  
Natural Frequencies ◽  
Model Parameters ◽  
Modal Damping ◽  
Torsional Damping ◽  
Analysis Of Results ◽  
Torsional Frequency ◽  
Signal Processing Methods ◽  
Parameter Values ◽  
Future Work

This paper is concerned with the experimental measurement and modelling of the torsional damping levels of a back-to-back gearbox rig. The aims of the investigation were to experimentally measure and analyse modal damping levels for the first nine torsional natural frequencies; to optimize damping parameters for modelling and to assess any limitations of the models for future work. Standard signal processing methods were used to determine modal damping levels from measured torsional frequency responses, with good confidence in the results. A damping sensitivity analysis for the two frequency domain receptance (FDR) models was used to determine optimum damping parameter values. Damping levels for six of nine natural frequencies were well matched with the experimental data. Discrepancies at other frequencies were attributed mainly to torsional-transverse coupling, present in the rig but not the model. Analysis of results for the ninth natural frequency determined a very low level of damping for the gearbox. It was also concluded that the model parameters may be used with confidence in a time domain receptance model for future investigations related to the test gearbox damping.

scholarly journals Spatial and Temporal Transferability of a Distributed Energy-Balance Glacier Melt Model

2011 ◽  
Vol 24 (5) ◽  
pp. 1480-1498 ◽  
Author(s):  
Andrew H. MacDougall ◽  
Gwenn E. Flowers
Keyword(s):  
Energy Balance ◽  
Yukon Territory ◽  
Model Parameters ◽  
Distributed Energy ◽  
Meteorological Forcing ◽  
Model Parameter ◽  
Model Transferability ◽  
Space And Time ◽  
Surface Ablation ◽  
Parameter Values

Abstract Modeling melt from glaciers is crucial to assessing regional hydrology and eustatic sea level rise. The transferability of such models in space and time has been widely assumed but rarely tested. To investigate melt model transferability, a distributed energy-balance melt model (DEBM) is applied to two small glaciers of opposing aspects that are 10 km apart in the Donjek Range of the St. Elias Mountains, Yukon Territory, Canada. An analysis is conducted in four stages to assess the transferability of the DEBM in space and time: 1) locally derived model parameter values and meteorological forcing variables are used to assess model skill; 2) model parameter values are transferred between glacier sites and between years of study; 3) measured meteorological forcing variables are transferred between glaciers using locally derived parameter values; 4) both model parameter values and measured meteorological forcing variables are transferred from one glacier site to the other, treating the second glacier site as an extension of the first. The model parameters are transferable in time to within a &lt;10% uncertainty in the calculated surface ablation over most or all of a melt season. Transferring model parameters or meteorological forcing variables in space creates large errors in modeled ablation. If select quantities (ice albedo, initial snow depth, and summer snowfall) are retained at their locally measured values, model transferability can be improved to achieve ≤15% uncertainty in the calculated surface ablation.

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