A common model to explain similarities between injection-induced and natural earthquake swarms

2021 ◽  
Author(s):  
Philippe Danre ◽  
Louis De Barros ◽  
Frédéric Cappa
Keyword(s):  
Effective Stress ◽  
Stress Drop ◽  
Mechanical Model ◽  
Cluster Size ◽  
Earthquake Swarms ◽  
Aseismic Slip ◽  
Physical Processes ◽  
Total Moment ◽  
Seismic Swarms ◽  
Volume Of Fluids

<p>Fluid injections at depth can trigger seismic swarms and aseismic deformations. Similarly, some natural sequences of seismicity occur clustered in time and space, without a distinguishable mainshock. They are usually interpreted as driven by fluid and/or aseismic processes. Those seismic swarms, natural or injection-induced, present similarities in their behavior, such as a seismic front migration. The effective stress drop, defined as a ratio between seismic moment and cluster size, is also weak for all swarms, when compared to usual earthquakes values. However, the physical processes that drive both types of swarms, and that can explain such similarities are still poorly understood. Here, we propose a mechanical model in which the fluid primarily induces an aseismic slip, which then triggers and drives seismicity within and on the edges of the active zone. This model is validated using a global and precise dataset of 16 swarms, from natural or induced origins, in different geological contexts. Consequently, our measurements of the migration velocity of the seismicity front, and of the effective stress drop for our swarms can be related to the seismic-to-aseismic moment. Using our model, we are then able to compute an estimate of the volume of fluids circulating during natural earthquake swarms, assuming the total moment is related to the volume of fluids. Our study highlights common characteristics and novel insights into the physical processes at play during seismic swarms.</p>

Fault parameters determined by near- and far-field data: The Wakasa Bay earthquake of March 26, 1963

1974 ◽  
Vol 64 (5) ◽  
pp. 1369-1382 ◽  
Author(s):  
Katsuyuki Abe
Keyword(s):  
Effective Stress ◽  
Stress Drop ◽  
P Wave ◽  
Slip Angle ◽  
Polarization Angle ◽  
S Wave ◽  
Seismological Data ◽  
Fault Parameters ◽  
Wakasa Bay ◽  
Dip Angle

Abstract The source process of the Wakasa Bay earthquake (M = 6.9, 35.80°N, 135.76°E, depth 4 km) which occurred near the west coast of Honshu Island, Japan, on March 26, 1963, is studied on the basis of the seismological data. Dynamic and static parameters of the faulting are determined by directly comparing synthetic seismograms with observed seismograms recorded at seismic near and far distances. The De Hoop-Haskell method is used for the synthesis. The average dislocation is determined to be 60 cm. The overall dislocation velocity is estimated to be 30 cm/sec, the rise time of the slip dislocation being determined as 2 sec. The other fault parameters determined, with supplementary data on the P-wave first motion, the S-wave polarization angle, and the aftershocks, are: source geometry, dip direction N 144°E, dip angle 68°, slip angle 22° (right-lateral strike-slip motion with some dip-slip component); fault dimension, 20 km length by 8 km width; rupture velocity, 2.3 km/sec (bilateral); seismic moment, 3.3 × 1025 dyne-cm; stress drop, 32 bars. The effective stress available to accelerate the fault motion is estimated to be about 40 bars. The approximate agreement between the effective stress and the stress drop suggests that most of the effective stress was released at the time of the earthquake.

Afterslip and slow slip events in the postseismic deformation of the 2016 Pedernales earthquake, Ecuador

2020 ◽  
Author(s):  
Frederique Rolandone ◽  
Jean-Mathieu nocquet ◽  
Patricia Mothes ◽  
Paul Jarrin ◽  
Mathilde Vergnolle
Keyword(s):  
Subduction Zones ◽  
Postseismic Deformation ◽  
Slow Slip ◽  
Aseismic Slip ◽  
Plate Interface ◽  
Slow Slip Events ◽  
North East ◽  
Rupture Area ◽  
Slip Event ◽  
Seismic Swarms

<p>In subduction zones, slip along the plate interface occurs in various modes including earthquakes, steady slip, and transient accelerated aseismic slip during either Slow Slip Events (SSE) or afterslip. We analyze continuous GPS measurements along the central Ecuador subduction segment to illuminate how the different slip modes are organized in space and time in the zone of the 2016 Mw 7.8 Pedernales earthquake. The early post-seismic period (1 month after the earthquake) shows large and rapid afterslip developing at discrete areas of the megathrust and a slow slip event remotely triggered (∼100 km) south of the rupture of the Pedernales earthquake. We find that areas of large and rapid early afterslip correlate with areas of the subduction interface that had hosted SSEs in years prior to the 2016 earthquake. Areas along the Ecuadorian margin hosting regular SSEs and large afterslip had a dominant aseismic slip mode that persisted throughout the earthquake cycle during several years and decades: they regularly experienced SSEs during the interseismic phase, they did not rupture during the 2016 Pedernales earthquake, they had large aseismic slip after it. Four years after the Pedernales earthquake, postseismic deformation is still on-going. Afterslip and SSEs are both involved in the postseimsic deformation. Two large aftershocks (Mw 6.7 & 6.8) occurred after the first month of postseismic deformation in May 18, and later in July 7 2016 two other large aftershocks (Mw 5.9 & 6.3) occurred, all were located north east of the rupture. They may have triggered their own postseismic deformation. Several seismic swarms were identified south and north of the rupture area by a dense network of seismic stations installed during one year after the Pedernales earthquakes, suggesting the occurrence of SSEs. Geodetically, several SSEs were detected during the postseismic deformation either in areas where no SSEs were detected previously, or in areas where regular seismic swarms and repeating earthquakes were identified. The SSEs may have been triggered by the stress increment due to aftershocks or due to afterslip.</p>

scholarly journals Remote monitoring of seismic swarms and the August 2016 seismic crisis of Brava, Cabo Verde, using array methods

2020 ◽  
Vol 20 (12) ◽  
pp. 3627-3638
Author(s):  
Carola Leva ◽  
Georg Rümpker ◽  
Ingo Wölbern
Keyword(s):  
Remote Monitoring ◽  
Significant Variation ◽  
Earthquake Swarms ◽  
Seismic Signals ◽  
Volcanic Island ◽  
Seismic Arrays ◽  
Cabo Verde ◽  
Seismic Swarms ◽  
Neighbouring Island ◽  
Seismic Crisis

Abstract. During the first two days of August 2016 a seismic crisis occurred on Brava, Cabo Verde, which – according to observations based on a local seismic network – was characterized by more than a thousand volcano-seismic signals. Brava is considered an active volcanic island, although it has not experienced any historic eruptions. Seismicity significantly exceeded the usual level during the crisis. We report on results based on data from a temporary seismic-array deployment on the neighbouring island of Fogo at a distance of about 35 km. The array was in operation from October 2015 to December 2016 and recorded a total of 1343 earthquakes in the region of Fogo and Brava; 355 thereof were localized. On 1 and 2 August we observed 54 earthquakes, 25 of which could be located beneath Brava. We further evaluate the observations with regards to possible precursors to the crisis and its continuation. Our analysis shows a significant variation in seismicity around Brava, but no distinct precursory pattern. However, the observations suggest that similar earthquake swarms commonly occur close to Brava. The results further confirm the advantages of seismic arrays as tools for the remote monitoring of regions with limited station coverage or access.

scholarly journals Remote monitoring of seismic swarms and the August 2016 seismic crisis of Brava, Cape Verde, using array methods

2020 ◽  
Author(s):  
Carola Leva ◽  
Georg Rümpker ◽  
Ingo Wölbern
Keyword(s):  
Remote Monitoring ◽  
Cape Verde ◽  
Seismic Network ◽  
Earthquake Swarms ◽  
Seismic Signals ◽  
Volcanic Island ◽  
Seismic Arrays ◽  
Seismic Swarms ◽  
Neighbouring Island ◽  
Seismic Crisis

Abstract. During the first two days of August 2016 a seismic crisis occurred on Brava, Cape Verde, which – according to observations based on a local seismic network – was characterized by more than thousand volcano-seismic signals. Brava is considered an active volcanic island, although it has not experienced any historic eruptions. Seismicity significantly exceeded the usual level during the crisis. We report on results based on data from a temporary seismic-array deployment on the neighbouring island of Fogo at a distance of about 35 km. The array was in operation from October 2015 to December 2016 and recorded a total of 1343 earthquakes, 355 thereof were localized. On 1 and 2 August we observed 54 earthquakes, 25 of which could be located beneath Brava. We further evaluate the observations with regards to possible precursors to the crisis and its continuation. Our analysis shows a migration of seismicity around Brava, but no distinct precursory pattern. However, the observations suggest that similar earthquake swarms commonly occur close to Brava. The results further confirm the advantages of seismic arrays as tools for the remote monitoring of regions with limited station coverage or access.

SIMPLIFICATION POSSIBILITIES FOR COUPLED THM MODELS OF ARTIFICIAL GROUND FREEZING IN THE CONSTRUCTION OF MINE SHAFTS

2021 ◽  
Vol 4 (1) ◽  
pp. 453-463
Author(s):  
M. A. Semin ◽  
Keyword(s):  
Mechanical Model ◽  
Soil Freezing ◽  
Underground Structures ◽  
Physical Processes ◽  
Reasonable Degree ◽  
Ground Freezing ◽  
The Media ◽  
Artificial Ground Freezing ◽  
Frozen Wall ◽  
The Relationship

An important stage in the design of the artificial ground freezing during the construc-tion of mine shafts (and other underground structures) is the simulation of deformation and heat transfer in the media to be frozen. This is necessary to calculate the required thicknesses of frozen wall, the time of its formation and the parameters of freezing stations. The choice of an adequate mathematical model is impossible without analyzing the significance and coupling of various physical processes occurring during the freezing of soil. Such an analysis allows se-lecting a reasonable degree of detailing of physical processes in the model: take into account all important factors and neglect the rest. This article proposes a methodology for analyzing the significance and coupling of such physical processes. For this, a general thermo-hydro-mechanical model of soil freezing has been formulated, a set of dimensionless complexes has been identified and classified, which determine the relationship between various physical pro-cesses. The transition from the general thermo-hydro-mechanical model to simpler models is possible only if the corresponding dimensionless complexes are small.

scholarly journals The near-source ground motion of the 6 August 1979 Coyote Lake, California, earthquake

1983 ◽  
Vol 73 (1) ◽  
pp. 201-218
Author(s):  
Hsui-Lin Liu ◽  
Donald V. Helmberger
Keyword(s):  
Ground Motion ◽  
Stress Drop ◽  
Personal Communication ◽  
Source Model ◽  
Total Moment ◽  
Motion Data ◽  
Rupture Length ◽  
Finite Fault ◽  
Source Data ◽  
Strong Ground

abstract A finite fault striking N24°W and extending to a depth of 10 km is proposed to explain the strong ground motion data for the 6 August 1979 Coyote Lake, California, earthquake (ML = 5.9). Our source model suggests that right-lateral faulting initiated at a depth of 8 km and ruptured toward the south with a velocity of 2.8 km/sec. This unilateral rupture can explain the large displacement recorded south of the epicenter. However, the waveform coherency across an array south and southwest of the epicenter suggests that the rupture length is less than 6 km. The maximum dislocation is about 120 cm in a small area near the hypocenter, and the total moment is estimated to be 3.5 ×1024 dyne-cm. An abrupt stopping phase which corresponds to a deceleration of right-lateral motion can explain the high peak acceleration recorded at array station 6. The stress drop in the hypocentral area is about 140 bars; the average stress drop over the entire rupture surface is 30 bars. The preferred finite-source model can predict the Pn1 waveforms and the beginning features in the teleseismic seismograms. No clear arrivals can be observed in the near-source data for the possible second and third smaller events suggested by Nabelek (personal communication).

scholarly journals Effective Stress Drop of Earthquake Clusters

2017 ◽  
Vol 107 (5) ◽  
pp. 2247-2257 ◽  
Author(s):  
Tomáš Fischer ◽  
Sebastian Hainzl
Keyword(s):  
Effective Stress ◽  
Stress Drop ◽  
Earthquake Clusters

scholarly journals Aseismic transient slip on the Gofar transform fault, East Pacific Rise

2020 ◽  
Vol 117 (19) ◽  
pp. 10188-10194 ◽  
Author(s):  
Yajing Liu ◽  
Jeffrey J. McGuire ◽  
Mark D. Behn
Keyword(s):  
East Pacific Rise ◽  
Rupture Propagation ◽  
Slow Slip ◽  
Aseismic Slip ◽  
Transform Faults ◽  
Brittle Ductile Transition ◽  
East Pacific ◽  
Seismic Swarms ◽  
Underlying Mechanisms ◽  
Earthquake Sequences

Oceanic transform faults display a unique combination of seismic and aseismic slip behavior, including a large globally averaged seismic deficit, and the local occurrence of repeating magnitude (M) ∼6 earthquakes with abundant foreshocks and seismic swarms, as on the Gofar transform of the East Pacific Rise and the Blanco Ridge in the northeast Pacific Ocean. However, the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear. Here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults. In the model, strong dilatancy strengthening, supported by seismic imaging that indicates enhanced fluid-filled porosity and possible hydrothermal circulation down to the brittle–ductile transition, effectively stabilizes along-strike seismic rupture propagation and results in rupture barriers where aseismic transients arise episodically. The modeled slow slip migrates along the barrier zones at speeds ∼10 to 600 m/h, spatiotemporally correlated with the observed migration of seismic swarms on the Gofar transform. Our model thus suggests the possible prevalence of episodic aseismic transients in M ∼6 rupture barrier zones that host active swarms on oceanic transform faults and provides candidates for future seafloor geodesy experiments to verify the relation between aseismic fault slip, earthquake swarms, and fault zone hydromechanical properties.

Sign in / Sign up

Export Citation Format

Share Document