scholarly journals Nearly Magnitude‐Invariant Stress Drops in Simulated Crack‐Like Earthquake Sequences on Rate‐and‐State Faults with Thermal Pressurization of Pore Fluids

2020 ◽  
Vol 125 (3) ◽  
Author(s):  
Stephen M. Perry ◽  
Valère Lambert ◽  
Nadia Lapusta
Keyword(s):  
Pore Fluids ◽  
Thermal Pressurization ◽  
Stress Drops ◽  
Earthquake Sequences

Stress-Drop Scaling of the 2016 Gyeongju and 2017 Pohang Earthquake Sequences Using Coda-Based Methods

2020 ◽  
Vol 110 (5) ◽  
pp. 2047-2057 ◽  
Author(s):  
Gyeongdon Chai ◽  
Seung-Hoon Yoo ◽  
Junkee Rhie ◽  
Tae-Seob Kang
Keyword(s):  
Stress Drop ◽  
Focal Depth ◽  
Earthquake Sequence ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Tectonic Earthquake ◽  
Good Opportunity ◽  
Gyeongju Earthquake ◽  
Stress Drops ◽  
Earthquake Sequences

ABSTRACT Two M 5 earthquakes struck the southeastern Korean Peninsula in September 2016 and November 2017, causing damage near the epicentral areas. We analyze the stress-drop scaling of these two earthquake sequences using coda-based methods and Bayesian inversion. The 2016 Gyeongju earthquake sequence is a typical earthquake sequence generated by tectonic processes. In contrast, the 2017 Pohang earthquake sequence is believed to be related to fluid injections conducted for the development of enhanced geothermal systems. As the two sequences occurred in the same tectonic regime, our study provides a good opportunity to compare the stress-drop scaling between a tectonic earthquake sequence and an earthquake sequence influenced by fluid injections. We found that the stress drops of events in the Pohang sequence are lower than those of the Gyeongju sequence with similar magnitude. Although it is likely that this difference results from focal depth variations, a reduction of stress drop due to fluid injections cannot be ruled out.

scholarly journals Earthquake rupture properties in presence of thermal -pressurization of pore fluids

2021 ◽  
Author(s):  
P. Martin Mai ◽  
Jagdish Vyas ◽  
Alice-Agnes Gabriel ◽  
Thomas Ulrich
Keyword(s):  
Shear Zone ◽  
Negative Correlation ◽  
Rise Time ◽  
Slip Rate ◽  
Half Width ◽  
Earthquake Rupture ◽  
Pore Fluids ◽  
Hydraulic Diffusivity ◽  
Thermal Pressurization ◽  
Rupture Speed

<p>Frictional heat generated in the fault core during earthquake rupture can raise the fluid pressure in the slip zone. Such increase of fluid pressure decreases the effective normal stress and thereby lowers the frictional strength of the fault. Therefore, thermal pressurization (TP) of pore fluid affects earthquake rupture processes including nucleation, propagation, and arrest. While the effects of pore pressure and fluid flow rate on dynamic weakening of faults are qualitatively understood, a detailed analysis of how TP affects  earthquake rupture parameters is needed to further deepen our understanding. </p><p>In this study, we investigate the role of two key TP parameters -- hydraulic diffusivity and shear-zone half-width -- earthquake dynamics and kinematic source properties (slip, peak slip-rate, rupture speed and rise time). We conduct  a suite of 3D dynamic rupture simulations applying a rate-and-state dependent friction law (with strong velocity weakening) coupled with thermal-pressurization of pore fluids. Simulations are carried out with the open source software SeisSol (www.seissol.org). The temporal evolution of rupture parameters over ~1’000 randomly  distributed on-fault receivers is statistically analyzed in terms of  mean variations of rupture parameters and correlations among rupture parameters. </p><p>Our simulations reveal that mean slip decreases with increasing hydraulic diffusivity, whereas mean peak slip-rate and rupture speed remain nearly constant. On the other hand, we observe only a slight decrease of mean slip with increasing shear-zone half-width, whereas mean peak slip-rate and rupture speed show clear decrease. The faster diffusion of pore pressure as hydraulic diffusivity increases promotes faster increase of the effective normal stress (and fault strength) behind the main rupture front, reducing the rise time and, therefore also affecting mean slip. An increase in shear-zone half- width represents a heat source distributed over larger fault normal distance causing a second-order effect on mean slip. Additionally, our simulations reveal correlations among rupture parameters: 1) slip has weak negative correlation with peak slip-rate and negligible correlation with rupture speed, but a positive correlation with rise time, 2) peak slip-rate has a strong positive correlation with rupture speed, but a strong negative correlation with rise time, 3) rupture speed has strong negative correlation with rise time. We observe little or negligible effects of variations of hydraulic diffusivity and shear-zone half- width on the correlations between rupture parameters. Overall, our study builds a fundamental understanding on how thermal pressurization of pore fluids affects dynamic and thereby kinematic earthquake rupture properties. Our findings are thus important for the earthquake source modeling community, and particularly, for assessing seismic hazard due to induced events in geo-reservoirs.</p>

scholarly journals Direct Characterization of the Relation between the Mechanical Response and Microstructure Evolution in Aluminum by Transmission Electron Microscopy In Situ Straining

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1431
Author(s):  
Seiichiro Ii ◽  
Takero Enami ◽  
Takahito Ohmura ◽  
Sadahiro Tsurekawa
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Ion Beam ◽  
Elastic Behavior ◽  
Annealed Specimen ◽  
Displacement Curve ◽  
Dislocation Loops ◽  
Transmission Electron ◽  
Stress Drops

Transmission electron microscopy in situ straining experiments of Al single crystals with different initial lattice defect densities have been performed. The as-focused ion beam (FIB)-processed pillar sample contained a high density of prismatic dislocation loops with the <111> Burgers vector, while the post-annealed specimen had an almost defect-free microstructure. In both specimens, plastic deformation occurred with repetitive stress drops (∆σ). The stress drops were accompanied by certain dislocation motions, suggesting the dislocation avalanche phenomenon. ∆σ for the as-FIB Al pillar sample was smaller than that for the post-annealed Al sample. This can be considered to be because of the interaction of gliding dislocations with immobile prismatic dislocation loops introduced by the FIB. The reloading process after stress reduction was dominated by elastic behavior because the slope of the load–displacement curve for reloading was close to the Young’s modulus of Al. Microplasticity was observed during the load-recovery process, suggesting that microyielding and a dislocation avalanche repeatedly occurred, leading to intermittent plasticity as an elementary step of macroplastic deformation.

Distribution of earthquake sequences in the Mediterranean

1973 ◽  
Vol 111 (1) ◽  
pp. 2158-2162 ◽  
Author(s):  
Dana Proch�zkov�
Keyword(s):  
The Mediterranean ◽  
Earthquake Sequences
Sign in / Sign up

Export Citation Format

Share Document