Far-field tsunami data assimilation for the 2015 Illapel earthquake

2019 ◽  
Vol 219 (1) ◽  
pp. 514-521 ◽  
Author(s):  
Y Wang ◽  
K Satake ◽  
R Cienfuegos ◽  
M Quiroz ◽  
P Navarrete
Keyword(s):  
Data Assimilation ◽  
Near Field ◽  
Source Parameters ◽  
Deep Ocean ◽  
Seismic Source ◽  
Far Field ◽  
Complementary Method ◽  
East Pacific ◽  
2015 Illapel Earthquake ◽  
Illapel Earthquake

SUMMARY The 2015 Illapel earthquake (Mw 8.3) occurred off central Chile on September 16, and generated a tsunami that propagated across the Pacific Ocean. The tsunami was recorded on tide gauges and Deep-ocean Assessment and Reporting of Tsunami (DART) tsunameters in east Pacific. Near-field and far-field tsunami forecasts were issued based on the estimation of seismic source parameters. In this study, we retroactively evaluate the potentiality of forecasting this tsunami in the far field based solely on tsunami data assimilation from DART tsunameters. Since there are limited number of DART buoys, virtual stations are assumed by interpolation to construct a more complete tsunami wavefront for data assimilation. The comparison between forecasted and observed tsunami waveforms suggests that our method accurately forecasts the tsunami amplitudes and arrival time in the east Pacific. This approach could be a complementary method of current tsunami warning systems based on seismic observations.

Stochastic Source Model for Strong Motion Prediction

2018 ◽  
Vol 9 (2) ◽  
pp. 1-22
Author(s):  
S. Sangeetha ◽  
S.T.G. Raghukanth
Keyword(s):  
Near Field ◽  
Source Parameters ◽  
Strong Motion ◽  
Seismic Source ◽  
Source Model ◽  
Spectral Density Function ◽  
Correlation Lengths ◽  
Rupture Area ◽  
Power Spectral ◽  
Finite Fault

The article aims at developing a stochastic model which simulates spatial distribution of slip on the fault plane. This is achieved by analysing a large dataset of 303 finite-fault rupture models from 152 past earthquakes with varying fault mechanisms and in the magnitude range of 4.11-9.12. New scaling relations to predict the seismic source parameters such as fault length, fault width, rupture area, mean and standard deviation of slip have been derived for distinct fault mechanisms. The developed methodology models the spatial variability of slip as a two-dimensional von Karman power spectral density function (PSD) and correlation lengths are estimated. The proposed stochastic slip model is validated by comparing the simulated near-field ground response with the recorded data available for the 20th September 1999 Chi-Chi earthquake, Taiwan.

The delayed aftershocks of the Illapel Earthquake Mw 8.3, 2015, Chile

2021 ◽  
Author(s):  
Franco Lema ◽  
Mahesh Shrivastava
Keyword(s):  
Tide Gauge ◽  
Stress Transfer ◽  
Large Earthquake ◽  
Seismic Source ◽  
Coulomb Stress ◽  
Coulomb Stress Changes ◽  
Finite Fault ◽  
Stress Changes ◽  
2015 Illapel Earthquake ◽  
Illapel Earthquake

<p>The delayed aftershocks 2018 Mw 6.2 on April 10 and Mw 5.8 on Sept 1 and 2019 Mw 6.7 on January 20, Mw 6.4 on June 14, and Mw 6.2 on November 4, associated with the Mw 8.3 2015 Illapel Earthquake occurred in the ​​central Chile. The seismic source of this earthquake has been studied with the GPS, InSAR and tide gauge network. Although there are several studies performed to characterize the robust aftershocks and the variations in the field of deformation induced by the megathrust, but there are still aspects to be elucidated of the relationship between the transfer of stresses from the interface between plates towards delayed aftershocks with the crustal structures with seismogenic potential. Therefore, the principal objective of this study is to understand how the stress transfer induced by the 2015 Illapel earthquake of the heterogeneous rupture mechanism to intermediate-deep or crustal earthquakes. For this, coulomb stress changes from  finite fault model of the Illapel earthquake and with the biggest aftershocks in year 2015 are used. These cumulative stress pattern provides substantial evidences for the delayed aftershocks in this region. The subducting Challenger Fault Zone and Juan Fernandez Ridge heterogeneity are existing feature, which releases the accumulated coulomb stress changes and provide delayed aftershocks.  Therefore along with stress induced by a large earthquake such as Mw 8.3 from Illapel 2015 along with biggest aftershocks, have a direct mechanism that may activate the  delayed aftershocks. Our study suggests  the activation of crustal faults in this research as a risk assessment factor for the evaluating in the seismic context of the region and useful for another subduction zone.</p>

Near-field strain in DAS-based microseismic observation

Geophysics ◽  
2021 ◽  
pp. 1-49
Author(s):  
Ge Jin ◽  
Frantisek Stanek ◽  
Bin Luo
Keyword(s):  
Hydraulic Fracture ◽  
Fiber Optic ◽  
Moment Tensor ◽  
Near Field ◽  
Source Parameters ◽  
Field Strain ◽  
Far Field ◽  
Normal Strain ◽  
S Wave ◽  
Sign Patterns

Microseismic monitoring with surface or downhole geophone arrays has been commonly used in tracking subsurface deformation and fracture networks during hydraulic fracturing operations. Recently, the use of fiber-optic DAS technology has improved microseismic acquisition to a new level with unprecedentedly high spatial resolution and low cost. Deploying fiber-optic cables in horizontal boreholes allows very close observation of these micro-sized earthquakes and captures their full wavefield details. We show that DAS-based microseismic profiles present a seldomly reported near-field strain signal between the P- and S-wave arrivals. This near-field signal shows monotonically increasing (or decreasing) temporal variation, which resembles the previously reported near-field observations of large earthquakes. To understand the near-field strain behavior, we provide a mathematical expression of the analytic normal strain solution that reveals the near-field, intermediate-near-field, intermediate-far-field, and far-field components. Synthetic DAS strain records of hydraulic-fracture-induced microseismic events can be generated using this analytic solution with the Brune source model. The polarity sign patterns of the near-field and far-field terms in these synthetics are linked to the corresponding source mechanism’s radiation patterns. These polarity sign patterns are demonstrated to be sensitive to the source orientations by rotating the moment tensor in different directions. A field data example is compared to the synthetic result and a qualitative match is shown. The microseismic near-field signals detected by DAS have potential value in hydraulic fracture monitoring by providing a means to better constrain microseismic source parameters that characterize the source magnitude, source orientation, and temporal source evolution, and therefore better reflect the geomechanical response of the hydraulically fractured environment in the unconventional reservoirs.

Expected impact of the 2016 central Italy earthquakes on the local gravity field

2020 ◽  
Author(s):  
Federica Riguzzi ◽  
Hongbo Tan ◽  
Chong-yang Shen
Keyword(s):  
Gravity Field ◽  
Half Space ◽  
Near Field ◽  
Source Parameters ◽  
Central Italy ◽  
Far Field ◽  
Dislocation Theory ◽  
Local Gravity ◽  
Vertical Displacements ◽  
Gnss Observations

<p>We have modelled the surface volume and gravity changes caused by the three mainshocks (moment magnitudes Mw 6.0, 5.9, 6.5) occurred during the last seismic period started on 2016, August 24 in central Italy. Our calculations start from the source parameters estimated by the inversion of the largest dataset of InSAR and GNSS observations ever managed in Italy after earthquake occurrences, based on the half-space elastic dislocation theory. The vertical displacements modelled after the 2016 events allow to infer a substantial unbalance between the subsided and uplifted volumes. In particular, we detected ~106∙10<sup>6</sup> m<sup>3</sup> of hangingwall subsidence against ~37∙10<sup>6</sup> m<sup>3</sup> of footwall uplift, that accounts for ~74% of the total volume mobilization. From the ratio between the footwall and total deformed volumes, we have computed an average fault dip of ~47°, in line with the values retrieved by seismological methods. The total gravity variations which affected the study area are of the order of ~1 μGal (1 μGal = 10<sup>−8</sup> ms<sup>−2</sup>) in the far field, and ~170 μGal in the near field.<br>The area affected within a gravity change of 1 μGal is ~140 km long and ~57 km wide, parallel to the Apennines chain. The larger contribution is given by positive variations which account for the tensional style of deformation and larger subsided area.</p>

Loreto Intermediate Depth Earthquake of 26 May 2019 (Northeast Peru): Source Parameters by Inversion of Local to Regional Waveforms and Strong-Motion Observations

2021 ◽  
Author(s):  
Hernando Tavera ◽  
Bertrand Delouis ◽  
Arturo Mercado ◽  
David Portugal
Keyword(s):  
Near Field ◽  
Source Parameters ◽  
Waveform Inversion ◽  
Strong Motion ◽  
Seismic Source ◽  
Slab Geometry ◽  
Nazca Plate ◽  
Strong Motion Data ◽  
Ground Shaking ◽  
Motion Data

Abstract The Loreto earthquake of 26 May 2019 occurred below the extreme northeast part of Peru at a depth of 140 km within the subducting Nazca plate at a distance of 700 km from the trench Peru–Chile. The orientation of the seismic source was obtained from waveform inversion in the near field using velocity and strong-motion data. The rupture occurred in normal faulting corresponding to a tensional process with T axis oriented in east–west direction similar to the direction of convergence between the Nazca and South America plates. The analysis of the strong-motion data shows that the levels of ground shaking are very heterogeneous with values greater than 50 Gal up to distances of 300 km; the maximum recorded acceleration of 122 Gal at a distance of 100 km from the epicenter. The Loreto earthquake is classified as a large extensional event in the descending Nazca slab in the transition from flat-slab geometry to greater dip.

scholarly journals Review of Recent Tsunami Observation by Offshore Cabled Observatory

2009 ◽  
Vol 4 (6) ◽  
pp. 489-497 ◽  
Author(s):  
Hiroyuki Matsumoto ◽  
◽  
Yoshiyuki Kaneda
Keyword(s):  
Global Positioning System ◽  
Kuril Island ◽  
Near Field ◽  
Deep Ocean ◽  
Far Field ◽  
Bottom Pressure ◽  
Tsunami Observations ◽  
Global Positioning ◽  
Tsunami Signal ◽  
Field Event

This paper discusses near- and far-field tsunami observations at the Hokkaido, Japan, offshore cabled observatory, focusing on the 2006 Kuril Island earthquake (Mw 8.3) as a far-field event and the 2008 off-Tokachi earthquake (Mw 6.8) as a near-field event. The Kuril Islands earthquake was detected as a series of tsunami signals by 2 bottom pressure gauges roughly 1 hour after the earthquake. Tsunami amplitudes observed offshore were 3 cm and off-coastal amplitudes were a few tens of centimeters. In the 2008 near-field off-Tokachi earthquake (Mw 6.8), a tsunami signal was detected simultaneously with the earthquake, which had a source amplitude of 4 cm. Our tsunami calculation reproduced the first wave well, but discrepancies about arrival time and amplitude arose for the second and later waves. Offshore tsunami sensors such as bottom pressure gauges, deep-ocean assessment and reporting of tsunami (DART) buoys, and kinematic global positioning system (GPS) buoys may thus become keys in early tsunami warning once appropriate dataset processing is implemented.

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