scholarly journals Dependences of the Omori and Gutenberg–Richter parameters

2019 ◽  
pp. 149-165 ◽  
Author(s):  
V. B. Smirnov ◽  
A. V. Ponomarev ◽  
S. A. Stanchits ◽  
M. G. Potanina ◽  
A. V. Patonin ◽  
...  
Keyword(s):  
Time Delay ◽  
Stress State ◽  
Axial Loading ◽  
B Value ◽  
Exponential Dependence ◽  
Parameter Estimates ◽  
Aftershock Activity ◽  
Uniform Compression ◽  
Effective Strength ◽  
Aftershock Sequences

Laboratory experiments on studying the aftershock regime are carried out with sandstone specimens under different axial loading and uniform compression and constant pore pressure. The aftershock sequences are modeled by the scenario of stepwise increasing axial loading of a specimen with strain control ensuring regular generation of aftershock sequences. The experiments are conducted on intact specimens and on the specimens with preliminarily formed shear macrofractures simulating natural faults. The experiments were conducted with multichannel recording of the acoustic emission (AE) signals which made it possible to locate the AE sources. Several types of the dependence of the acoustic activity relaxation parameters (parameters p and c of the modified Omori law and the Gutenberg–Richter b-value) on the level of acting stresses are revealed. The b-value decreases with the growth of axial stresses at all levels of uniform compression. In the case of fracture on the preexisting fault, the Omori relaxation parameter p increases with the growth of axial stresses whereas parameter c (the time delay before the onset of relaxation) decreases with the growth of axial stresses and increases with the rise of the level of uniform compression. In the case of a fracture of an undamaged specimen, parameter p remains unchanged as the axial stresses grow, whereas parameter c increases slightly. Parameter variations in the case of a complex stress state with both varying deviatoric (differential stresses) and spherical parts (effective pressure) of the stress tensor take on a unified form when expressed in terms of Coulomb stresses. It is hypothesized that the time delay of the aftershock activity relaxation is determined by the kinetics of fracture in accordance with the kinetic concept of strength in solids. This hypothesis is supported by exponential dependence of parameter c on stresses and on the effective strength of the medium revealed in the experiments. Under this hypothesis, the dependences of parameter c on the Coulomb stresses can be unified for different effective strength values with the use of Zhurkov’s formula for durability of materials. The obtained parameter estimates for the dependence of c on strength and stresses suggest that the c value is determined by the difference of the strength and the acting stresses, indicating how far the stress state of the medium is from the critical state corresponding to the ultimate strength.

Two Foreshock Sequences Post Gulia and Wiemer (2019)

2020 ◽  
Vol 91 (5) ◽  
pp. 2843-2850 ◽  
Author(s):  
Kelian Dascher-Cousineau ◽  
Thorne Lay ◽  
Emily E. Brodsky
Keyword(s):  
Puerto Rico ◽  
Real Time ◽  
Exact Result ◽  
Monte Carlo Sampling ◽  
B Value ◽  
Aftershock Sequence ◽  
Traffic Light ◽  
B Values ◽  
Aftershock Sequences ◽  
Abrupt Changes

Abstract Recognizing earthquakes as foreshocks in real time would provide a valuable forecasting capability. In a recent study, Gulia and Wiemer (2019) proposed a traffic-light system that relies on abrupt changes in b-values relative to background values. The approach utilizes high-resolution earthquake catalogs to monitor localized regions around the largest events and distinguish foreshock sequences (reduced b-values) from aftershock sequences (increased b-values). The recent well-recorded earthquake foreshock sequences in Ridgecrest, California, and Maria Antonia, Puerto Rico, provide an opportunity to test the procedure. For Ridgecrest, our b-value time series indicates an elevated risk of a larger impending earthquake during the Mw 6.4 foreshock sequence and provides an ambiguous identification of the onset of the Mw 7.1 aftershock sequence. However, the exact result depends strongly on expert judgment. Monte Carlo sampling across a range of reasonable decisions most often results in ambiguous warning levels. In the case of the Puerto Rico sequence, we record significant drops in b-value prior to and following the largest event (Mw 6.4) in the sequence. The b-value has still not returned to background levels (12 February 2020). The Ridgecrest sequence roughly conforms to expectations; the Puerto Rico sequence will only do so if a larger event occurs in the future with an ensuing b-value increase. Any real-time implementation of this approach will require dense instrumentation, consistent (versioned) low completeness catalogs, well-calibrated maps of regionalized background b-values, systematic real-time catalog production, and robust decision making about the event source volumes to analyze.

SELF-ORGANIZED CRITICALITY MODEL FOR EARTHQUAKES: QUIESCENCE, FORESHOCKS AND AFTERSHOCKS

1999 ◽  
Vol 09 (12) ◽  
pp. 2249-2255 ◽  
Author(s):  
S. HAINZL ◽  
G. ZÖLLER ◽  
J. KURTHS
Keyword(s):  
Power Law ◽  
B Value ◽  
Power Law Distribution ◽  
Aftershock Activity ◽  
Omori Law ◽  
Self Organized ◽  
Spatiotemporal Clustering ◽  
Self Organized Criticality ◽  
Clustering Of Events ◽  
Foreshock Activity

We introduce a crust relaxation process in a continuous cellular automaton version of the Burridge–Knopoff model. Analogously to the original model, our model displays a robust power law distribution of event sizes (Gutenberg–Richter law). The principal new result obtained with our model is the spatiotemporal clustering of events exhibiting several characteristics of earthquakes in nature. Large events are accompanied by a precursory quiescence and by localized fore- and aftershocks. The increase of foreshock activity as well as the decrease of aftershock activity follows a power law (Omori law) with similar exponents p and q. All empirically observed power law exponents, the Richter B-value, p and q and their variability can be reproduced simultaneously by our model, which depends mainly on the level of conservation and the relaxation time.

Aftershock decay of three recent strong earthquakes in the Levant

1998 ◽  
Vol 88 (6) ◽  
pp. 1580-1587
Author(s):  
Nitzan Rabinowitz ◽  
David M. Steinberg
Keyword(s):  
Heat Flow ◽  
Gulf Of Aqaba ◽  
P Value ◽  
Aftershock Activity ◽  
P Values ◽  
Strong Earthquakes ◽  
Omori’S Law ◽  
Southwest Coast ◽  
Slow Decay ◽  
Aftershock Sequences

Abstract Aftershock sequences are studied from three recent strong earthquakes in the Levant: the MW = 7.1 earthquake of 22 November 1995 and the ML = 5.8 earthquake of 3 August 1993, both in the Gulf of Aqaba, and the MW = 6.8 earthquake of 9 October 1996 off the southwest coast of Cyprus. The modified Omori's law provides a good fit to the decay of aftershock activity for both events. The two sequences from the Gulf of Aqaba have rather low p values (0.90 in 1993 and 0.75 in 1995), reflecting slow decay of the aftershock activity. This may be attributed to low heat flow close to the epicenters. For the Cyprus sequence, the p value is 1.09, similar to that of many other sequences around the globe.

Background Seismicity before and after the 1976 Ms 7.8 Tangshan Earthquake: Is Its Aftershock Sequence Still Continuing?

2020 ◽  
Author(s):  
Yue Liu ◽  
Jiancang Zhuang ◽  
Changsheng Jiang
Keyword(s):  
Aftershock Sequence ◽  
Tangshan Earthquake ◽  
Aftershock Activity ◽  
Background Rate ◽  
Epidemic Type Aftershock Sequence ◽  
Aftershock Sequences ◽  
Background Seismicity ◽  
Before And After ◽  
Large Earthquakes ◽  
Current Stage

Abstract The aftershock zone of the 1976 Ms 7.8 Tangshan, China, earthquake remains seismically active, experiencing moderate events such as the 5 December 2019 Ms 4.5 Fengnan event. It is still debated whether aftershock sequences following large earthquakes in low-seismicity continental regions can persist for several centuries. To understand the current stage of the Tangshan aftershock sequence, we analyze the sequence record and separate background seismicity from the triggering effect using a finite-source epidemic-type aftershock sequence model. Our results show that the background rate notably decreases after the mainshock. The estimated probability that the most recent 5 December 2019 Ms 4.5 Fengnan District, Tangshan, earthquake is a background event is 50.6%. This indicates that the contemporary seismicity in the Tangshan aftershock zone can be characterized as a transition from aftershock activity to background seismicity. Although the aftershock sequence is still active in the Tangshan region, it is overridden by background seismicity.

Recent seismic swarms in the Tjornes fracture zone, N-Iceland

2020 ◽  
Author(s):  
Kristín Jónsdóttir ◽  
Gunnar B. Guðmundsson ◽  
Luigi Passarelli ◽  
Sigurjón Jónsson ◽  
Yesim Cubuncu ◽  
...  
Keyword(s):  
Fracture Zone ◽  
Seismic Station ◽  
B Value ◽  
Correlation Study ◽  
Seismic Network ◽  
The North ◽  
Aftershock Sequences ◽  
Volcanic Seismicity ◽  
Seismic Swarms ◽  
Seismic Moment Release

<p>The Tjörnes fracture zone (TFZ) in N-Iceland is a seismically active zone with on average 4000 earthquakes detected annually since 1993 by the regional seismic network operated by the Icelandic Meteorological Office (IMO). Most of the earthquakes occur offshore and with only one seismic station on the Grímsey island north of Iceland, the seismic network detects earthquakes down to magnitude M-0.5. The fracture zone, essentially a transform between the northern volcanic zone of Iceland and the Mid-Atlantic Ridge north of Iceland, has three major segments; the Grímsey Oblique Rift (GOR) farthest to the North which accounts for 60% of the seismicity of the TFZ, the Húsavík-Flatey Fault (HFF) in the middle, where 38% of the TFZ earthquakes occur and the least active Dalvík Lineament (DL) farthest to the south (only 2% of TFZ seismicity). The IMO’s seismic catalogue clearly draws up the most active segments of the TFZ, where each extends laterally roughly 100 km. The largest earthquakes occur on the HFF where the accumulated seismic moment release is an order of magnitude higher than the GOR and three orders of magnitude higher than the DL.</p><p>There are other interesting differences between the segments. There are several known central volcanoes aligned along the GOR and the oblique rifting is likely to cause both tectonic and volcanic seismicity which shows up as a catalogue of many but similarly sized earthquakes, in other words a catalogue with a higher b-value than the neighbouring HFF. Despite these differences, seismic swarms, without a clear mainshock or aftershock sequences, counting thousands of earthquakes with a duration of a few days upto weeks, are recorded every 2-3 years both in GOR and HFF. In late March 2019, one of this seismic swarms took place on GOR, mostly on a single NNE-SSW striking fault near Kópasker. Relative earthquake locations draw the fault up nicely and in addition a few shorter faults with similar strike of 15°deg. The temporal evolution of the swarm shows an upwards migration and how the seismicity starts at the middle of the fault, jumps a little to the north and migrates in two days to the southern end of the fault over 7 km. When that point is reached, the largest earthquake in the swarm takes place, M4.2, however in the very northern end of the fault. The focal mechanism of this largest event shows a left-lateral strike-slip as do the smaller earthquakes. A b-value plot of the 2300 earthquakes that were recorded during the swarm reveal a value of 1.2, which is typical for volcanic seismicity. The size of active fault is considerable larger than expected from a M4.2 earthquake and the question rises if part of the motion is taken up as aseismic slip.</p><p>We will present examples of recent swarms in the TFZ along with new results of a cross-correlation study of the waveforms recorded during the swarm activity.</p>

Optimal aspect ratio of interference fits for maximum load transfer capacity

2005 ◽  
Vol 40 (2) ◽  
pp. 177-184 ◽  
Author(s):  
D Castagnetti ◽  
E Dragoni
Keyword(s):  
Stress State ◽  
Aspect Ratio ◽  
Load Transfer ◽  
Load Capacity ◽  
Frictional Coefficient ◽  
Axial Loading ◽  
Maximum Load ◽  
Material Response ◽  
Optimal Ratio ◽  
Joint Design

The stress state in frictional interference fits under torsional and axial loading is examined. The optimal ratio between the inside and outside diameters of the hub is calculated, which maximizes the load transmitted by the joint. Design formulae and charts are provided, giving the most efficient aspect ratio of the hub for all practical situations. It is found that the maximum load capacity is achieved for an aspect ratio in the range from 0.5 to 0.7, regardless of the frictional coefficient (up to 1), of the kind of loading (torsional or axial), and of the material response (brittle or ductile).

scholarly journals Pseudoprospective Evaluation of the Foreshock Traffic-Light System in Ridgecrest and Implications for Aftershock Hazard Assessment

2020 ◽  
Vol 91 (5) ◽  
pp. 2828-2842 ◽  
Author(s):  
Laura Gulia ◽  
Stefan Wiemer ◽  
Gianfranco Vannucci
Keyword(s):  
Real Time ◽  
Hazard Assessment ◽  
Monitoring Network ◽  
B Value ◽  
Traffic Light ◽  
B Values ◽  
Background Value ◽  
Light System ◽  
Aftershock Sequences ◽  
Aftershock Hazard

Abstract The Mw 7.1 Ridgecrest earthquake sequence in California in July 2019 offered an opportunity to evaluate in near-real time the temporal and spatial variations in the average earthquake size distribution (the b-value) and the performance of the newly introduced foreshock traffic-light system. In normally decaying aftershock sequences, in the past studies, the b-value of the aftershocks was found, on average, to be 10%–30% higher than the background b-value. A drop of 10% or more in “aftershock” b-values was postulated to indicate that the region is still highly stressed and that a subsequent larger event is likely. In this Ridgecrest case study, after analyzing the magnitude of completeness of the sequences, we find that the quality of the monitoring network is excellent, which allows us to determine reliable b-values over a large range of magnitudes within hours of the two mainshocks. We then find that in the hours after the first Mw 6.4 Ridgecrest event, the b-value drops by 23% on average, compared to the background value, triggering a red foreshock traffic light. Spatially mapping the changes in b values, we identify an area to the north of the rupture plane as the most likely location of a subsequent event. After the second, magnitude 7.1 mainshock, which did occur in that location as anticipated, the b-value increased by 26% over the background value, triggering a green traffic light. Finally, comparing the 2019 sequence with the Mw 5.8 sequence in 1995, in which no mainshock followed, we find a b-value increase of 29% after the mainshock. Our results suggest that the real-time monitoring of b-values is feasible in California and may add important information for aftershock hazard assessment.

scholarly journals CHARACTERISTICS OF SEISMIC EXCITATIONS IN CORINTH GULF (GREECE)

2017 ◽  
Vol 50 (3) ◽  
pp. 1379
Author(s):  
M. Mesimeri ◽  
V. Karakostas ◽  
E. Papadimitriou ◽  
G. Tsaklidis
Keyword(s):  
Seismic Hazard Assessment ◽  
B Value ◽  
Seismic Excitations ◽  
Active Deformation ◽  
Corinth Gulf ◽  
Gulf Of Corinth ◽  
Aftershock Sequences ◽  
Spatio Temporal ◽  
Spatial Size ◽  
Skewness And Kurtosis

Seismic excitations occur as mainshock-aftershock sequences (MS-AS) encompassing a strong event called mainshock with the largest magnitude in the set, or as earthquake swarms (ES) when a distinctive main event is absent. In regions as the gulf of Corinth, where active deformation is manifested with frequent seismicity bursts, it is important to distinguish MS-AS from ES for providing information on the physical process of earthquake generation and contribute to the seismic hazard assessment. For this purpose, a highly accurate local earthquake catalogue was compiled and an effort was made for clusters identification after establishing certain criteria based on spatio-temporal seismicity properties. The skewness and kurtosis of moment release history were calculated considering the normalized time of every event in a cluster since the starting time of the cluster and its seismic moment. For MS-AS we found large positive values for skewness and kurtosis contrary to ES that exhibit negative to low positive values for skewness and even lower values for kurtosis.In order to verify the classification of clusters, the b-value, the spatial size and the number of events of each cluster were examined. Finally, a scaling relation between the length of the rupture zone and magnitude derived for the MS-AS sequences.

scholarly journals A study of aftershocks of 20 October 1991 Uttarkashi earthquake

MAUSAM ◽  
2022 ◽  
Vol 46 (4) ◽  
pp. 435-444
Author(s):  
R S. DATTATRAYAM ◽  
V.P. KAMBLE
Keyword(s):  
Decay Constant ◽  
Source Parameters ◽  
Temporal Distribution ◽  
B Value ◽  
Aftershock Sequence ◽  
Himalayan Region ◽  
Aftershock Activity ◽  
Field Surveys ◽  
Macroseismic Observations ◽  
Good Agreement

The Uttarkashi earthquake of 20 October 1991, which caused widespread damage in the Galhwal Himalayan region, was followed by a prominent aftershock. activity extending over a period of about two months. The aftershock activity was monitored using temporary networks established after the mainshock and the permanent stations in operation in the region. About 142 aftershocks could be located accurately using the data of these stations. The b-value of the Gutenberg-Richter's relationship for the aftershock sequence works out to be 0.6. The temporal distribution of the aftershocks suggests a hyperbolic decay with a decay constant (p) of 1.17. Macroseismic observations derived from field surveys show good agreement with the instrumentally determined source parameters.  

The foreshock-aftershock sequence of the March 20 1966 earthquake in the Republic of Congo

1970 ◽  
Vol 60 (4) ◽  
pp. 1245-1258 ◽  
Author(s):  
John Lahr ◽  
Paul W. Pomeroy
Keyword(s):  
Dynamic Range ◽  
B Value ◽  
High Gain ◽  
Aftershock Sequence ◽  
Confidence Limits ◽  
B Values ◽  
Aftershock Sequences ◽  
Successful Prediction ◽  
Seismograph Station ◽  
The Republic

abstract The activity associated with the Congo earthquake of March 20 1966 (mb = 6.5 to 7) was studied with emphasis on the time and magnitude distributions. The data were recorded at the Abéché, Chad, seismograph station operated by Lamont-Doherty Geological Observatory. Over a period of about 70 days, 815 earthquakes with magnitude (mb) greater than or equal to 3.3 were recorded, and they form the basis for this study. The aftershocks are distributed with magnitude (mb) according to the formula long n = a - bm with b = 1.05 ± 0.07 at the 95 per cent confidence limits. The foreshocks have b = 1.06 ± 0.35 at the 95 per cent confidence limits. These b values are in general agreement with b values derived from other aftershock sequences throughout the world. Some authors have suggested that foreshocks may have a lower b value than background activity and that this difference might be used in earthquake prediction. In this paper, an evaluation is made of the limitations of this method of prediction. Assuming that such a difference in b values does exist, it is found that a closely spaced network of high-gain seismographs with wide dynamic range would be required to assure successful prediction.

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