scholarly journals Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes

2021 ◽  
Author(s):  
Serge A. Shapiro ◽  
Carsten Dinske
Keyword(s):  
Stress Drop ◽  
Induced Seismicity ◽  
Quantitative Characteristic ◽  
High Stress ◽  
Operation Time ◽  
Average Stress ◽  
Induced Earthquakes ◽  
Effective Stresses ◽  
Seismicity Rates

AbstractSometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.

Mutual relations between tress drop of induced earthquakes and fault cohesion.

2021 ◽  
Author(s):  
Serge Shapiro
Keyword(s):  
Stress Drop ◽  
Quantitative Characteristic ◽  
High Stress ◽  
Operation Time ◽  
Additional Contribution ◽  
Induced Earthquakes ◽  
Gas Field ◽  
Mutual Relations ◽  
The One

<p>In some regions a significant stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and the stress drop. We propose a simple and rather general phenomenological model of the stress drop of induced earthquakes. Our model suggests that a high stress drop can result from a decrease in cohesion of initially inactive faults that are seismically activated by long-term fluid operations. On the one hand, the increasing stress drop can lead to an increase in the seismogenic index with the time of fluid operations. On the other hand, a production/injection caused change of the pore pressure can also cause a systematic increase in the stress drop. This can provide an additional contribution to the growth of seismogenic index (and thus to the seismic risk) with operation time of reservoirs.</p><p>The case study of Groningen gas field provides interesting information in this respect. A significant stress drop of some induced earthquakes at Groningen can be explained by activating preexisting cohesive normally-stressed fault systems. Seismic events on such faults lead to the drop of their cohesion due to the rupture process. This cohesion drop contributes directly to the earthquake stress drop. The production-related increase of the differential stress in the reservoir leads to an increasing number of seismically activated more cohesive faults. This leads in turn to an increasing seismogenic index. The seismogenic index seems to be quite low at Groningen. However, it increases systematically with the production time. One of reasons of this behavior can be related to the average cohesion of involved faults as it is mentioned above. An additional effect contributing to this increase is a systematically increasing stress drop due to the production-related pressure depletion increasing the effective stress in the reservoir. A growing seismogenic index can result in an increasing with time maximum possible magnitude, Mmax.</p>

Improved approach for stress drop estimation and its application to an induced earthquake sequence in Oklahoma

2020 ◽  
Vol 223 (1) ◽  
pp. 233-253
Author(s):  
X Chen ◽  
R E Abercrombie
Keyword(s):  
Stress Drop ◽  
Source Parameters ◽  
High Stress ◽  
Temporal Variations ◽  
Earthquake Source ◽  
Average Stress ◽  
Corner Frequency ◽  
Resolution Limit ◽  
Spectral Fitting ◽  
Spatio Temporal

SUMMARY We calculate source parameters for fluid-injection induced earthquakes near Guthrie, Oklahoma, guided by synthetic tests to quantify uncertainties. The average stress drop during an earthquake is a parameter fundamental to ground motion prediction and earthquake source physics, but it has proved hard to measure accurately. This has limited our understanding of earthquake rupture, as well as the spatio-temporal variations of fault strength. We use synthetic tests based on a joint spectral-fitting method to define the resolution limit of the corner frequency as a function of the maximum frequency of usable signal, for both individual spectra and the average from multiple stations. Synthetic tests based on stacking analysis find that an improved stacking approach can recover the true input stress drop if the corner frequencies are within the resolution limit defined by joint spectral-fitting. We apply the improved approach to the Guthrie sequence, using different wave types and signal-to-noise criteria to understand the stability of the calculated stress drop values. The results suggest no systematic scaling relationship of stress drop for M ≤ 3.1 earthquakes, but larger events (M ≥ 3.5) tend to have higher average stress drops. Some robust spatio-temporal variations can be linked to the triggering processes and indicate possible stress heterogeneity within the fault zone. Tight clustering of low stress drop events at the beginning stage of the sequence suggests that pore pressure influences earthquake source processes. Events at shallow depth have lower stress drop compared to deeper events. The largest earthquake occurred within a cluster of high stress drop events, likely rupturing a strong asperity.

scholarly journals Parametric analysis of the elastohydrodynamic lubrication efficiency on induced seismicity

2020 ◽  
Vol 222 (1) ◽  
pp. 517-525 ◽  
Author(s):  
Chiara Cornelio ◽  
Marie Violay
Keyword(s):  
Stress Drop ◽  
Induced Seismicity ◽  
Parametric Analysis ◽  
Elastohydrodynamic Lubrication ◽  
In Situ Stress ◽  
Induced Earthquakes ◽  
Dynamic Stress Drop ◽  
Static Stress Drop ◽  
In Situ Stress Field

SUMMARY During reservoir stimulations, the injection of fluids with variable viscosities can trigger seismicity. Several fault lubrication mechanisms have been invoked to explain the dynamic stress drop occurring during those seismic events. Here, we perform a parametric analysis of the elastohydrodynamic fault lubrication mechanism to assess its efficiency during fluid-induced earthquakes. The efficiency of the mechanism is measured with the dimensionless Sommerfeld number S. Accordingly, we analysed eight well-documented cases of induced seismicity associated with the injection of fluids whose viscosities range from 1 mPa s (water) to 100 mPa s (proppant). We collected information related to the in situ stress field, fault orientation and geometry, moment of magnitude and static stress drop of the events. These parameters allow us to analyse the variation in the Sommerfeld number. Our results show that the estimated dynamic friction on the fault during the event is compatible with the fault weakening predicted by the elastohydrodynamic lubrication theory, particularly for highly viscous fluids.

scholarly journals Transanal total mesorectal excision: short- and long-term results of the first hundred cases of a certified colorectal cancer center in Germany

2021 ◽  
Author(s):  
Vinzenz Völkel ◽  
Sabine Schatz ◽  
Teresa Draeger ◽  
Michael Gerken ◽  
Monika Klinkhammer-Schalke ◽  
...  
Keyword(s):  
Local Recurrence ◽  
Tumor Resection ◽  
Operation Time ◽  
Cancer Center ◽  
Transanal Total Mesorectal Excision ◽  
Local Tumor ◽  
Long Term Outcomes ◽  
Free Survival ◽  
Short And Long Term

Abstract Background Since 2010, laparoscopic transanal total mesorectal excision (TaTME) has been increasingly used for low and very low rectal cancer. It is supposed to improve visibility and access to the dissection planes in the pelvis. This study reports on short- and long-term outcomes of the first 100 consecutive patients treated with TaTME in a certified German colorectal cancer center. Patients and methods Data were derived from digital patient files and official cancer registry reports for patients with TaTME tumor surgery between July 2014 and January 2020. The primary outcome was the 3-year local recurrence rate and local recurrence-free survival (LRFS). Secondary endpoints included overall survival (OAS), disease-free survival (DFS), operation time, completeness of local tumor resection, lymph node resection, and postoperative complications. The Kaplan–Meier method was employed for the survival analyses; competing risks were considered in the time-to-event analysis. Results During the observation period, the average annual operation time decreased from 272 to 178 min. Complete local tumor resection was achieved in 97% of the procedures. Major postoperative complications (Clavien–Dindo 3–4) occurred in 11% of the cases. At a median follow-up time of 2.7 years, three patients had suffered from a local recurrence. Considering competing risks, this corresponds to a 3-year cumulative incidence rate for local recurrence of 2.2% and a 3-year LRFS of 81.9%. 3-year OAS was 82.9%, and 3-year DFS was 75.7%. Conclusion TaTME is associated with favorable short and long-term outcomes. Since it is technically demanding, structured training programs and more research on the topic are indispensable.

Seismic quiescence, stress drops, and asperities in the New Hebrides arc

1983 ◽  
Vol 73 (1) ◽  
pp. 219-236
Author(s):  
M. Wyss ◽  
R. E. Habermann ◽  
Ch. Heiniger
Keyword(s):  
High Stress ◽  
Plate Boundary ◽  
Seismic Quiescence ◽  
Data Set ◽  
Seismicity Rate ◽  
Seismic Gaps ◽  
Main Shocks ◽  
Seismicity Rates ◽  
New Hebrides ◽  
Stress Drops

abstract The rate of occurrence of earthquakes shallower than 100 km during the years 1963 to 1980 was studied as a function of time and space along the New Hebrides island arc. Systematic examination of the seismicity rates for different magnitude bands showed that events with mb < 4.8 were not reported consistently over time. The seismicity rate as defined by mb ≧ 4.8 events was examined quantitatively and systematically in the source volumes of three recent main shocks and within two seismic gaps. A clear case of seismic quiescence could be shown to have existed before one of the large main shocks if a major asperity was excluded from the volume studied. The 1980 Ms = 8 rupture in the northern New Hebrides was preceded by a pattern of 9 to 12 yr of quiescence followed by 5 yr of normal rate. This pattern does not conform to the hypothesis that quiescence lasts up to the mainshock which it precedes. The 1980 rupture also did not fully conform to the gap hypothesis: half of its aftershock area covered part of a great rupture which occurred in 1966. A major asperity seemed to play a critical role in the 1966 and 1980 great ruptures: it stopped the 1966 rupture, and both parts of the 1980 double rupture initiated from it. In addition, this major asperity made itself known by a seismicity rate and stress drops higher than in the surrounding areas. Stress drops of 272 earthquakes were estimated by the MS/mb method. Time dependence of stress drops could not be studied because of changes in the world data set of Ms and mb values. Areas of high stress drops did not correlate in general with areas of high seismicity rate. Instead, outstandingly high average stress drops were observed in two plate boundary segments with average seismicity rate where ocean floor ridges are being subducted. The seismic gaps of the central and northern New Hebrides each contain seismically quiet regions. In the central New Hebrides, the 50 to 100 km of the plate boundary near 18.5°S showed an extremely low seismicity rate during the entire observation period. Low seismicity could be a permanent property of this location. In the northern New Hebrides gap, seismic quiescence started in mid-1972, except in a central volume where high stress drops are observed. This volume is interpreted as an asperity, and the quiescence may be interpreted as part of the preparation process to a future large main shock near 13.5°S.

P-wave spectra for ML 5 foreshocks, aftershocks, and isolated earthquakes near Parkfield, California

1981 ◽  
Vol 71 (2) ◽  
pp. 423-436
Author(s):  
Willian H. Bakun ◽  
Thomas V. McEvilly
Keyword(s):  
Stress Drop ◽  
High Stress ◽  
P Wave ◽  
Wave Radiation ◽  
Focal Region ◽  
Wave Spectra ◽  
Rupture Length ◽  
Main Shocks ◽  
Relative Stress ◽  
Fault Trace

abstract Wood-Anderson seismograms recorded at Mount Hamilton (MHC, 185 km, 327°), Santa Barbara (SBC, 180 km, 158°), and Tinemaha (TIN, 240 km, 56°) provide data for comparing P-wave spectra for two immediate (17-min) foreshocks, one early (55-hr) foreshock, two aftershocks, and two “isolated” Parkfield earthquakes. All are ML 5.0 shocks with epicenters within 7 km of the common epicenter of the 1934 and 1966 Parkfield main shocks. The set of events is well suited for testing the hypothesis that foreshocks are high-stress-drop sources. Calculated stress drops are controlled by source directivity at azimuths aligned with the fault break (at MHC and SBC). P-wave radiation from the three foreshocks is focused along one fault trace azimuth, suggesting that foreshock sources are characterized by pronounced unilateral rupture expansion. At TIN, broadside to the fault where directivity has minimum effect on calculated relative stress drop, the two immediate foreshocks are higher stress-drop sources. The early foreshock is a low-to-average stress-drop source, indicating the possibility that stress concentration is a rapidly occurring phenomenon in rupture nucleation. Alternatively, the stress field is highly variable on the scale of 2 to 3 km in the focal region of an impending earthquake with a rupture length of 20 to 30 km.

scholarly journals Statistical physics models for aftershocks and induced seismicity

2018 ◽  
Vol 377 (2136) ◽  
pp. 20170397 ◽  
Author(s):  
Molly Luginbuhl ◽  
John B. Rundle ◽  
Donald L. Turcotte
Keyword(s):  
Induced Seismicity ◽  
Statistical Physics ◽  
Aftershock Sequence ◽  
Induced Earthquakes ◽  
Aftershock Activity ◽  
Gas Field ◽  
Natural Time ◽  
Parkfield Earthquake ◽  
Groningen Gas Field

A standard approach to quantifying the seismic hazard is the relative intensity (RI) method. It is assumed that the rate of seismicity is constant in time and the rate of occurrence of small earthquakes is extrapolated to large earthquakes using Gutenberg–Richter scaling. We introduce nowcasting to extend RI forecasting to time-dependent seismicity, for example, during an aftershock sequence. Nowcasting uses ‘natural time’; in seismicity natural time is the event count of small earthquakes. The event count for small earthquakes is extrapolated to larger earthquakes using Gutenberg–Richter scaling. We first review the concepts of natural time and nowcasting and then illustrate seismic nowcasting with three examples. We first consider the aftershock sequence of the 2004 Parkfield earthquake on the San Andreas fault in California. Some earthquakes have higher rates of aftershock activity than other earthquakes of the same magnitude. Our approach allows the determination of the rate in real time during the aftershock sequence. We also consider two examples of induced earthquakes. Large injections of waste water from petroleum extraction have generated high rates of induced seismicity in Oklahoma. The extraction of natural gas from the Groningen gas field in The Netherlands has also generated very damaging earthquakes. In order to reduce the seismic activity, rates of injection and withdrawal have been reduced in these two cases. We show how nowcasting can be used to assess the success of these efforts. This article is part of the theme issue ‘Statistical physics of fracture and earthquakes’.

Analysis on the Creep Mechanism of 12Cr-Mo-W-0.25V Steel Based on Long-Term Stress Relaxation Test Data

2016 ◽  
Vol 853 ◽  
pp. 158-162
Author(s):  
Jie Zhao ◽  
Tie Shan Cao ◽  
Cong Qian Cheng ◽  
Hui Fang Li
Keyword(s):  
Stress Relaxation ◽  
Test Data ◽  
Activation Volume ◽  
High Stress ◽  
Relaxation Curve ◽  
Relaxation Test ◽  
Dislocation Slip ◽  
Stress Relaxation Test ◽  
Steel Base

The current paper investigates on the creep behavior of 12Cr-Mo-W-0.25V heat resistant steel base on the long-term stress relaxation test data. It is shows that the stress relaxation curve can be divided into 2 stages: the high stress stage has higher apparent activation volume of 79~350 b3 and the low stress stage is 35~78 b3. Besides, the Helmholtz free energy at the high stress stage is 827~1034 kJ/mol which is higher than 210~252 kJ/mol of the low stress stage. Taking both apparent activation volume and activation energy into account, it is assumed that the high stress stage is mainly controlled by dislocation slip and the low stress stage is more related to diffusion.

scholarly journals Short-term and long-term outcomes of robotic, laparoscopic and open radical gastrectomy in gastric cancer: A single-center retrospective study

2019 ◽  
Author(s):  
Weifan Zhang ◽  
Xinhui Zhao ◽  
Zhao Liu ◽  
Hui Dang ◽  
Lei Meng ◽  
...  
Keyword(s):  
Gastric Cancer ◽  
Lymph Nodes ◽  
Learning Curve ◽  
Operation Time ◽  
Open Gastrectomy ◽  
Short Term ◽  
Term Outcome ◽  
Long Term Outcome ◽  
Estimated Blood Loss

Abstract Background: Few studies on the comparison among robotic, laparoscopic, and open gastrectomy had been reported in gastric cancer . The goal of this study was to evaluate the advantages of robotic-assisted gastrectomy (RAG) by comparing with laparoscopic-assisted gastrectomy(LAG) and open gastrectomy (OG). Methods: 147 gastric cancer patients who underwent gastrectomy were enrolled and retrospectively analyzed between January 2017 and July 2019. Short-term outcomes such as operation time, intraoperative estimated blood loss(EBL),number of retrieved lymph nodes, postoperative recovery, learning curve, and long-term outcome such as overall survival(OS) was compared among RAG, LAG and OG groups. Results: RAG group included 47 patients, 44 in the LAG, and 61 in the OG. Basic information such as gender, age, BMI, ASA degree were similar among three groups, and there were no statistically significances in pathological TNM staging, tumor resection extent, resection margin, methods of reconstruction( P ＞0.05). The cumulative sum(CUSUM) method showed that learning curve of RAG reached stability after 17 cases . For short-term outcomes, the RAG group had the shortest EBL( P =0.033), the shortest time to first flatus( P ＜0.001), shortest time to first intake liquid diet ( P =0.004),shortest postoperative hospital stay ( P =0.023)and the largest number of retrieved lymph nodes( P =0.044),the longest operation time( P ＜0.001), the most expensive treatment cost( P ＜0.001),however, there were no significant differences in postoperative drainage, postoperative white blood cell(WBC)count and early complications among three group( P ＞0.05). In addition to long-term outcome, similar OS was observed in three groups. Conclusion: Compared with LAG and OG, RAG has certain advantages in short-term outcomes and is a safe and reliable surgical method. But still need further prospective, multi-center research to confirm this.

Sign in / Sign up

Export Citation Format

Share Document