scholarly journals A Shallow Earthquake Swarm Close to Hydrocarbon Activities: Discriminating between Natural and Induced Causes for the 2018–2019 Surrey, United Kingdom, Earthquake Sequence

2019 ◽  
Vol 90 (6) ◽  
pp. 2095-2110 ◽  
Author(s):  
Stephen P. Hicks ◽  
James Verdon ◽  
Brian Baptie ◽  
Richard Luckett ◽  
Zoë K. Mildon ◽  
...  
Keyword(s):  
Source Parameters ◽  
Earthquake Swarm ◽  
Sedimentary Basins ◽  
B Value ◽  
Earthquake Sequence ◽  
Fault System ◽  
Current Evidence ◽  
Maximum Magnitude ◽  
Earthquake Parameters ◽  
Industrial Activities

ABSTRACT Earthquakes induced by subsurface industrial activities are a globally emotive issue, with a growing catalog of induced earthquake sequences. However, attempts at discriminating between natural and induced causes, particularly for anomalously shallow seismicity, can be challenging. An earthquake swarm during 2018–2019 in southeast England with a maximum magnitude of ML 3.2 received great public and media attention because of its proximity to operating oilfields. It is therefore vital and timely to provide a detailed characterization of the earthquake sequence at present, and to decide based on current evidence, whether the earthquakes were likely natural or induced. We detected 168 low‐magnitude earthquakes and computed detailed source parameters of these events. Most earthquakes occurred at a shallow depth of 2.3 km, >1  km deeper than the geological formations targeted by the oilfields, and laterally >3  km away from the drill sites. We combine the east–west‐trending cluster of the seismicity with 2D seismic reflection profiles to find the causative fault system for the earthquakes. A b‐value close to unity and strike‐slip faulting mechanisms are consistent with tectonic reactivation along a pre‐existing fault. Overall, we find no indicators in the earthquake parameters that would strongly suggest an induced source. Nor do we find any clear trends between seismicity and drilling activities based on operational logs provided by the operators. Injected volumes are near zero and monthly production amounts are many orders of magnitude smaller than other reported cases of extraction‐induced seismicity. On balance, and based on the available evidence, we find it currently unlikely that nearby industrial activities induced the seismic swarm. Most likely, the Surrey earthquakes offer a uniquely detailed insight into shallow seismicity within sedimentary basins. Nevertheless, self‐reporting of injection and production times and volumes by operators, and the lack of easily and publicly available oilfield operational data continues to be a point of concern for local residents.

Inversion of regional surface-wave spectra for source parameters of aftershocks from the 1992 Petrolia earthquake sequence

1995 ◽  
Vol 85 (3) ◽  
pp. 705-715
Author(s):  
Mark Andrew Tinker ◽  
Susan L. Beck
Keyword(s):  
Surface Wave ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Earthquake Sequence ◽  
Fault System ◽  
Accretionary Wedge ◽  
Wave Spectra ◽  
The North ◽  
Gorda Plate

Abstract Regional distance surface waves are used to study the source parameters for moderate-size aftershocks of the 25 April 1992 Petrolia earthquake sequence. The Cascadia subduction zone had been relatively seismically inactive until the onset of the mainshock (Ms = 7.1). This underthrusting event establishes that the southern end of the North America-Gorda plate boundary is seismogenic. It was followed by two separate and distinct large aftershocks (Ms = 6.6 for both) occurring at 07:41 and 11:41 on 26 April, as well as thousands of other small aftershocks. Many of the aftershocks following the second large aftershock had magnitudes in the range of 4.0 to 5.5. Using intermediate-period surface-wave spectra, we estimate focal mechanisms and depths for one foreshock and six of the larger aftershocks (Md = 4.0 to 5.5). These seven events can be separated into two groups based on temporal, spatial, and principal stress orientation characteristics. Within two days of the mainshock, four aftershocks (Md = 4 to 5) occurred within 4 hr of each other that were located offshore and along the Mendocino fault. These four aftershocks comprise one group. They are shallow, thrust events with northeast-trending P axes. We interpret these aftershocks to represent internal compression within the North American accretionary prism as a result of Gorda plate subduction. The other three events compose the second group. The shallow, strike-slip mechanism determined for the 8 March foreshock (Md = 5.3) may reflect the right-lateral strike-slip motion associated with the interaction between the northern terminus of the San Andreas fault system and the eastern terminus of the Mendocino fault. The 10 May aftershock (Md = 4.1), located on the coast and north of the Mendocino triple junction, has a thrust fault focal mechanism. This event is shallow and probably occurred within the accretionary wedge on an imbricate thrust. A normal fault focal mechanism is obtained for the 5 June aftershock (Md = 4.8), located offshore and just north of the Mendocino fault. This event exhibits a large component of normal motion, representing internal failure within a rebounding accretionary wedge. These two aftershocks and the foreshock have dissimilar locations in space and time, but they do share a north-northwest oriented P axis.

Focal depths and source parameters of the Rocky Mountain House earthquake swarm from digital data at Edmonton

1984 ◽  
Vol 21 (10) ◽  
pp. 1105-1113 ◽  
Author(s):  
C. J. Rebollar ◽  
E. R. Kanasewich ◽  
E. Nyland
Keyword(s):  
Epicentral Distance ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Focal Depth ◽  
Rocky Mountain ◽  
Small Variation ◽  
B Value ◽  
Digital Data ◽  
The Difference ◽  
Stress Drops

Seismic records at Edmonton (EDM) and Suffield (SES) between January 1976 and February 1980 show 220 events with magnitudes less than 4 originating near Rocky Mountain House. Many of these events show well defined Sn, Sg, and Pg phases and a small variation in the difference of Sg − Sn and Sg − Pg. Analysis of the theoretical travel times using a structure determined for central Alberta yields an average focal depth of 20 ± 5 km and an average epicentral distance of 175 ± 5 km southwest of Edmonton for 40 of these events. Because Sn was not clear on the remainder, it was not possible to get focal depths for all the events.Seismic moments of 80 events with local magnitudes from 1.6 to 3.5 were found to be in the range of 6.6 ± 2 × 1018 to 7.9 ± 2 × 1020 dyn∙cm (6.6 ± 2 × 1013 to 7.9 ± 2 × 1015 N∙cm). A relationship between local magnitude and seismic moment was log (M0) = 1.3ML + 16.6. This is similar to that determined for California. Source radii, where they could be determined, were 500 ± 50 m and stress drops were 0.75 ± 0.75 bar (75 ± 75 kPa).The energy release of 263 events recorded at EDM from the Rocky Mountain House area was 5.6 × 1017 erg (5.6 × 1010 J). The b value for this earthquake swarm was 0.8, similar to that observed in other parts of western Canada.The depths of focus, the low stress drops, and the statistical similarity to other natural earthquake sequences suggest that at least part of the swarm is of a natural origin.

The earthquake hazard alert of September 1982 in Southern Tobago

1988 ◽  
Vol 78 (4) ◽  
pp. 1550-1562
Author(s):  
F. D. Morgan ◽  
G. Wadge ◽  
J. Latchman ◽  
W. P. Aspinall ◽  
D. Hudson ◽  
...  
Keyword(s):  
Energy Release ◽  
Near Field ◽  
Earthquake Swarm ◽  
Earthquake Hazard ◽  
B Value ◽  
Fault System ◽  
Daily Monitoring ◽  
The North ◽  
Late Neogene ◽  
Future Earthquake

Abstract An earthquake swarm that occurred in the vicinity of the island of Tobago (West Indies) during the latter half of 1982 was monitored in the near-field by a five-station seismograph network. The monitoring of the swarm eventually led to the issuing of a potential earthquake hazard alert, 3 days prior to the major energy release (earthquake magnitude mb = 5.2). We discuss the reasons for issuing this alert. In particular, daily monitoring of the changing b value and energy release was used to constrain estimates of future earthquake behavior. The aftershock seismicity showed activity in a direction trending west to WNW. This is in good agreement with the focal mechanism of the main earthquake which showed right-lateral strike-slip motion along an E-W fault plane dipping steeply (71°) to the north. This active fault appears to form part of the previously unrecognized Southern Tobago Fault System for which there is evidence in the geology of the Late Neogene rocks of the island.

A Study on the Largest Hydraulic-Fracturing-Induced Earthquake in Canada: Observations and Static Stress-Drop Estimation

2020 ◽  
Author(s):  
Bei Wang ◽  
Rebecca M. Harrington ◽  
Yajing Liu ◽  
Honn Kao ◽  
Hongyu Yu
Keyword(s):  
Hydraulic Fracturing ◽  
Stress Drop ◽  
Risk Mitigation ◽  
Source Parameters ◽  
B Value ◽  
Corner Frequency ◽  
Maximum Magnitude ◽  
Maximum Earthquake Magnitude ◽  
Tectonic Earthquakes ◽  
Maximum Earthquake

ABSTRACT On 17 August 2015, an Mw 4.6 earthquake occurred northwest of Fort St. John, British Columbia, possibly induced by hydraulic fracturing (HF). We use data from eight broadband seismometers located ∼50  km from the hypocenter to detect and estimate source parameters of more than 300 events proximal to the mainshock. Stress-drop values estimated using seismic moment and corner frequency from single-event spectra and spectral ratios range from ∼1 to 35 MPa, within the typical range of tectonic earthquakes. We observe an ∼5-day delay between the onset of fluid injection and the mainshock, a b-value of 0.78 for the sequence, and a maximum earthquake magnitude larger than the prediction based on the total injection volume, suggesting that the Mw 4.6 sequence occurred on a pre-existing fault and that the maximum magnitude is likely controlled by tectonic conditions. Results presented here show that pre-existing fault structures should be taken into consideration to better estimate seismic hazard associated with HF operations and to develop schemes for risk mitigation in close proximity to HF wells.

Solving for Source Parameters Using Nested Array Data: A Case Study from the Canterbury, New Zealand Earthquake Sequence

2016 ◽  
Vol 174 (3) ◽  
pp. 875-893 ◽  
Author(s):  
Corrie Neighbors ◽  
E. S. Cochran ◽  
K. J. Ryan ◽  
A. E. Kaiser
Keyword(s):  
New Zealand ◽  
Source Parameters ◽  
Earthquake Sequence ◽  
Array Data

scholarly journals Fully probabilistic seismic source inversion – Part 1: Efficient parameterisation

2013 ◽  
Vol 5 (2) ◽  
pp. 1125-1162 ◽  
Author(s):  
S. C. Stähler ◽  
K. Sigloch
Keyword(s):  
Moment Tensor ◽  
Source Parameters ◽  
Practical Importance ◽  
Principal Component ◽  
Seismic Source ◽  
Empirical Orthogonal Functions ◽  
Time Function ◽  
Source Inversion ◽  
Source Time Function ◽  
Earthquake Parameters

Abstract. Seismic source inversion is a non-linear problem in seismology where not just the earthquake parameters themselves, but also estimates of their uncertainties are of great practical importance. Probabilistic source inversion (Bayesian inference) is very adapted to this challenge, provided that the parameter space can be chosen small enough to make Bayesian sampling computationally feasible. We propose a framework for PRobabilistic Inference of Source Mechanisms (PRISM) that parameterises and samples earthquake depth, moment tensor, and source time function efficiently by using information from previous non-Bayesian inversions. The source time function is expressed as a weighted sum of a small number of empirical orthogonal functions, which were derived from a catalogue of >1000 STFs by a principal component analysis. We use a likelihood model based on the cross-correlation misfit between observed and predicted waveforms. The resulting ensemble of solutions provides full uncertainty and covariance information for the source parameters, and permits to propagate these source uncertainties into travel time estimates used for seismic tomography. The computational effort is such that routine, global estimation of earthquake mechanisms and source time functions from teleseismic broadband waveforms is feasible.

Geodolite measurements near the Briones Hills, California, earthquake swarm of January 8, 1977

1978 ◽  
Vol 68 (1) ◽  
pp. 175-180
Author(s):  
J. C. Savage ◽  
W. H. Prescott
Keyword(s):  
Earthquake Swarm ◽  
Dislocation Model ◽  
Maximum Magnitude ◽  
Epicentral Area ◽  
Observable Change ◽  
Measuring Techniques ◽  
Significant Change ◽  
Tilt Change ◽  
Distance Measuring

abstract Two geodetic stations, the positions of which are frequently monitored by geodetic distance-measuring techniques, were located 5 and 10 km from the epicentral area of the Briones Hills earthquake swarm (maximum magnitude ML = 4.3) of January 1977. Although a 10 μradian postearthquake tilt change was recorded at a nearby tiltmeter, no significant change in geodetic distances could be detected at a sensitivity of at least 0.5 ppm. A simple dislocation model of the main earthquake in the swarm would predict no observable change in either tilt or geodetic distance.

scholarly journals Empirical Relationship for Assessing the Near-Field Horizontal Coseismic Displacement Using GPS Seismology Data

2021 ◽  
Vol 60 (1) ◽  
pp. 31-50
Author(s):  
Ryad Darawcheh ◽  
Riad Al Ghazzi ◽  
Mohamad Khir Abdul-wahed
Keyword(s):  
Near Field ◽  
Empirical Relationship ◽  
Active Faults ◽  
Historical Earthquakes ◽  
Dead Sea ◽  
Fault System ◽  
Coseismic Displacement ◽  
Data Set ◽  
Earthquake Parameters ◽  
Gps Station

In this research, a data set of horizontal GPS coseismic displacement in the near-field has been assembled around the world in order to investigate a potential relationship between the displacement and the earthquake parameters. Regression analyses have been applied to the data of 120 interplate earthquakes having the magnitude (Mw 4.8-9.2). An empirical relationship for prediction near-field horizontal GPS coseismic displacement as a function of moment magnitude and the distance between hypocenter and near field GPS station has been established using the multi regression analysis. The obtained relationship allows assessing the coseismic displacements associated with some large historical earthquakes occurred along the Dead Sea fault system. Such a fair relationship could be useful for assessing the coseismic displacement at any point around the active faults.

scholarly journals The use of parallel computing for the high-resolution determination of earthquake source parameters

2019 ◽  
pp. 68-75
Author(s):  
A. S. Fomochkina ◽  
V. G. Bukchin
Keyword(s):  
Parallel Computing ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Nodal Plane ◽  
Earthquake Parameters ◽  
Earthquake Source Parameters ◽  
Detailed Search ◽  
High Degree ◽  
Special Case

Alongside the determination of the focal mechanism and source depth of an earthquake by direct examination of their probable values on a grid in the parameter space, also the resolution of these determinations can be estimated. However, this approach requires considerable time in the case of a detailed search. A special case of a shallow earthquake whose one nodal plane is subhorizontal is an example of the sources that require the use of a detailed grid. For studying these events based on the records of the long-period surface waves, the grids with high degree of detail in the angles of the focal mechanism are required. We discuss the application of the methods of parallel computing for speeding up the calculations of earthquake parameters and present the results of studying the strongest aftershock of the Tohoku, Japan, earthquake by this approach.

Source parameters and scaling relationships of small earthquakes in the northeastern Caribbean

1981 ◽  
Vol 71 (4) ◽  
pp. 1173-1190
Author(s):  
Arthur Frankel
Keyword(s):  
Seismic Moment ◽  
Dynamic Stress ◽  
Source Parameters ◽  
Earthquake Swarm ◽  
Fold Increase ◽  
Virgin Islands ◽  
Scaling Relationships ◽  
Short Period ◽  
Relative Stress ◽  
Stress Drops

abstract The seismic moments and stress drops of 23 earthquakes (1.1 ≦ M ≦ 2.4) that occurred during an earthquake swarm in the Virgin Islands were determined from the analysis of their P waveforms. The data consist of digitally recorded seismograms collected by a short-period seismic network operating in the northeastern Caribbean. The events of the swarm are particularly useful for comparing the relative stress drops of small earthquakes, because their source to receiver paths and focal mechanisms are very similar. The static stress drops calculated for these earthquakes varied from about 0.2 to 2 bars. The data clearly illustrate that the static and dynamic stress drops of these earthquakes generally increased with the size (moment) of the events. The fault radii for these shocks increased with seismic moment, but only by a factor of 2 for a 100-fold increase in seismic moment. The velocity waveforms of the larger events were systematically more impulsive than those of the smaller earthquakes. These observations imply that, for this set of earthquakes, the final fault radius is a function of the stress drop that occurs during the rupture process.

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