Adapting the Matched‐Filter Search to a Wide‐Aperture Network: An Aftershock Sequence and an Earthquake Swarm in Connecticut

2018 ◽  
Vol 108 (1) ◽  
pp. 524-532 ◽  
Author(s):  
William B. Frank ◽  
Rachel E. Abercrombie
Keyword(s):  
Matched Filter ◽  
Earthquake Swarm ◽  
Aftershock Sequence ◽  
Wide Aperture

The Norris Lake Earthquake Swarm of June Through September, 1993; Preliminary Findings

1994 ◽  
Vol 65 (2) ◽  
pp. 167-171 ◽  
Author(s):  
L.T. Long ◽  
A. Kocaoglu ◽  
R. Hawman ◽  
P.J.W. Gore
Keyword(s):  
Earthquake Swarm ◽  
Building Stone ◽  
Aftershock Sequence ◽  
Average Depth ◽  
Induced Earthquakes ◽  
Epicentral Area ◽  
Event Recorder ◽  
Significant Damage ◽  
The 1950S ◽  
Recreational Lake

Abstract During the summer of 1993, the residents in the Norris Lake community, Lithonia, Georgia, were bothered by an incessant swarm of earthquakes. The largest, a magnitude 2.7 on September 23, showed a normal aftershock decay and occurred after the main swarm. Over 10,000 earthquakes have been detected, of which perhaps 500 were felt. The earthquakes began June 8, 1993, with a 5-day swarm. The residents, accustomed to quarry explosions, suspected the quarries of irregular activities. To locate the source of the events, a visual recorder and a digital event recorder were placed in the epicentral area. Ten to 20 events were detected per day for the next three weeks. The swarm then escalated to a peak of over 100 per day by August 15, 1993. Activity following the peak died down to about 10 events per day. The magnitude 2.7 event of September 23 was followed by a normal aftershock sequence. The larger events were felt with intensity V within 2 km of their epicenter, and noticed (intensity II) to a distance of 15 km. Some incidents of cracked wallboard and foundations have been reported, but no significant damage has been documented. Preliminary locations, based on data from digital event recorders, suggest an average depth of 1.0 km. The hypocenters are in the Lithonia gneiss, a massive migmatite resistant to weathering and used locally as a building stone. The epicenters are 1 to 2 km south-southwest of the Norris Lake Community. The cause of the seismicity is not yet known. The earthquakes are characteristic of reservoir-induced earthquakes; however, Norris Lake is a small (96 acres), 2 to 5m deep recreational lake which has existed since the 1950s.

Episodic earthquake swarms in the Mineral Mountains, Utah driven by the Roosevelt hydrothermal system

2021 ◽  
Author(s):  
Maria Mesimeri ◽  
Kristine Pankow ◽  
Ben Baker ◽  
J. Mark Hale
Keyword(s):  
Hydrothermal System ◽  
Hot Springs ◽  
Matched Filter ◽  
Earthquake Swarm ◽  
Earthquake Swarms ◽  
Earthquake Catalog ◽  
Spatial And Temporal Patterns ◽  
University Of Utah ◽  
South Central ◽  
The University

<p> The Mineral Mountains are located in south-central Utah within the transition zone from the Basin and Range to Colorado Plateau physiographic provinces, near the Roosevelt Hot Springs. First evidence of swarm-like activity in the area was found in 1981, when a six-station temporary network detected a very energetic swarm of ~1,000 earthquakes. More recently, in mid-2016, a dense local broadband seismic network was installed around the Frontier Observatory for Research in Geothermal Energy (FORGE) in southcentral Utah, ~10 km west of the Mineral Mountains. Beginning in 2016, the University of Utah Seismograph Stations detected, located, and characterized 75 earthquakes beneath the Mineral Mountains. In this study, we build an enhanced earthquake catalog to confirm the episodic swarm-like nature of seismicity in the Mineral Mountains. We use the 75 cataloged earthquakes as templates and detect 1,000 earthquakes by applying a matched-filter technique. The augmented catalog reveals that seismicity in the Mineral Mountains occurs as short-lived earthquake swarms followed by periods of quiescence. Earthquake relocation of ~800 earthquakes shows that activity is concentrated in a <2 km long E-W striking narrow zone, ~4 km east of the Roosevelt hydrothermal system. Two fault orientations, both N-S and E-W parallel to the Opal Mound and Mag Lee faults, respectively, are observed after computing composite focal mechanisms of highly similar earthquakes. After examining the spatial and temporal patterns of the best recorded earthquake swarm in October 2019, we find that a complex mechanism of fluid diffusion and aseismic slip is responsible for the swarm evolution with migration velocities reaching 10 km/day. We hypothesize that these episodic swarms in the Mineral Mountains are primarily driven by migrating fluids that originate within the Roosevelt hydrothermal system.</p>

scholarly journals Detecting Real Earthquakes Using Artificial Earthquakes: On the Use of Synthetic Waveforms in Matched-Filter Earthquake Detection

2021 ◽  
Author(s):  
Calum Chamberlain ◽  
John Townend
Keyword(s):  
Focal Mechanism ◽  
Matched Filter ◽  
A Priori ◽  
Low Frequency ◽  
Aftershock Sequence ◽  
Filter Method ◽  
Detection Rates ◽  
Earthquake Detection ◽  
American Geophysical ◽  
American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. Matched-filters are an increasingly popular tool for earthquake detection, but their reliance on a priori knowledge of the targets of interest limits their application to regions with previously documented seismicity. We explore an extension to the matched-filter method to detect earthquakes and low-frequency earthquakes on local to regional scales. We show that it is possible to increase the number of detections compared with standard energy-based methods, with low false-detection rates, using suites of synthetic waveforms as templates. We apply this to a microearthquake swarm and an aftershock sequence, and to detect low-frequency earthquakes. We also explore the sensitivity of detections to the synthetic source's location and focal mechanism. Source-receiver geometry has a first-order control on how sensitive matched-filter detectors are to variations in source location and focal mechanism, and this likely applies to detections made using both synthetic and real templates.

From earthquake swarm to a main shock–aftershocks: the 2018 activity in West Bohemia/Vogtland

2020 ◽  
Vol 224 (3) ◽  
pp. 1835-1848
Author(s):  
M Bachura ◽  
T Fischer ◽  
J Doubravová ◽  
J Horálek
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
Earthquake Swarm ◽  
Seismic Energy ◽  
Aftershock Sequence ◽  
Double Difference ◽  
Differential Stress ◽  
West Bohemia ◽  
Spatio Temporal ◽  
Insight Into

SUMMARY In earthquake swarms, seismic energy is released gradually by many earthquakes without a dominant event, which offers detailed insight into the processes on activated faults. The swarm of May 2018 that occurred in West Bohemia/Vogtland region included more than 4000 earthquakes with ML =〈0.5, 3.8&x3009 x232A;and its character showed significant changes during the two weeks duration: what started as a pure earthquake swarm ended as a typical main shock–aftershock sequence. Based on precise double-difference relocations, four fault segments differing in strikes and dips were identified with similar dimensions. First, two segments of typical earthquake swarm character took place, and at the end a fault segment hosting a main shock–aftershock sequence was activated. The differences were observable in the earthquakes spatio-temporal evolutions (systematic versus disordered migration of the hypocentres), b-values (>1.3 for the swarm, <1 for the main shock–aftershocks), or the smoothness of seismic moment spatial distribution along the fault plane. Our findings can be interpreted by local variations of fault rheology, differential stress and/or smoothness of the faults surface, possibly related to the crustal fluids circulating along the fault plane and their interplay with the seismic cycle.

Earthquake swarms in West Bohemia-Vogtland and South-West Iceland: are they of similar nature?

2020 ◽  
Author(s):  
Josef Horálek ◽  
Hana Jakoubková ◽  
Jana Doubravová ◽  
Martin Bachura
Keyword(s):  
Seismic Moment ◽  
Earthquake Swarm ◽  
Aftershock Sequence ◽  
Earthquake Swarms ◽  
A Value ◽  
South West ◽  
Aftershock Sequences ◽  
West Bohemia ◽  
Reykjanes Peninsula ◽  
Seismic Moment Release

<p>Earthquake swarms occurred worldwide in diverse geological units, however, their origin is still unclear. West Bohemia-Vogtland represents one of the most active intraplate earthquake-swarm areas in Europe, South-West Iceland is characterized by intense interplate earthquake swarms. Both these areas exhibit high activity of crustal fluids.</p><p>We investigated earthquake swarms from W-Bohemia and from different areas in SW-Iceland: the Hengill volcanic complex, Ölfus transition zone (the edge of the SISZ), and Reykjanes Peninsula, from the perspective of their magnitude-time development, seismic moment release with time, the magnitude-frequency distribution and distribution of the inter-event times, and the space and time distribution of the foci. The aim was to determine the swarm characteristics that are dependent or vice-versa independent on the tectonic environment, and also the characteristics which should help us to distinguish more precisely earthquake swarms from mainshock-aftershock sequences.</p><p>We found that the frequency-magnitude (b-values) and inter-event-time distributions are similar for both areas, while total seismic moment release and its rate are much larger for the SW Icelandic activities compared to the W-Bohemia ones. One dominant short-term swarm phase with one or a few dominant events in which significant part of M<sub>0tot</sub> released, is typical of the SW Icelandic swarms, whereas the W-Bohemia swarms are characterised by stepwise seismic moment release, which is manifested by several swarm phases. MFDs of the SW-Iceland swarms indicate significantly lower a-value (number of M<sub>L</sub> > 0 evens), particularly of those on the Reykjanes Peninsula, compared to W-Bohemia swarms; it is due to the fact that considerable amount of M<sub>0tot </sub>released in quasi-mainshocks and the rest in aftershocks; lower a-value was also found for the W-Bohemian mainshock-aftershock sequence in 2014. The W-Bohemian swarms took place in a bounded focal zone consisting of several fault segments but the SW-Icelandic swarms correspond well to tectonic structures along the Mid Atlantic Ridge. We conclude that most of the W-Bohemia earthquake swarms were series of subswarms with one or more embedded mainshock-aftershock sequences, while the SW-Icelandic swarms (particularly those on the Reykjanes Peninsula appear to be a transition between earthquake swarm and mainshock-aftershock sequence. The W-Bohemia and SW-Iceland focal zones are characterized by complex system of short, differently oriented faults/fault segments; interestingly, the W-Bohemia and some SW-Icelandic focal zones exhibit coexistence of faults susceptible to earthquake swarms and differently oriented faults predisposed to common earthquakes (mainshock-aftershocks).</p>

Complex magmatic-tectonic interactions during the 2020 Makushin Volcano, Alaska, earthquake swarm

2021 ◽  
Author(s):  
Diana Roman ◽  
Federica Lanza ◽  
John Power ◽  
Cliff Thurber ◽  
Thomas Hudson
Keyword(s):  
Earthquake Swarm ◽  
Velocity Model ◽  
Aftershock Sequence ◽  
Double Difference ◽  
Magma Intrusion ◽  
Fault Plane Solutions ◽  
3D Velocity Model ◽  
Double Couple ◽  
Seismic Swarms ◽  
Lower Magnitude

<p>We investigate the processes driving<strong> </strong>a significant earthquake swarm that occurred between June and December 2020 on Unalaska Island, Alaska, ~12 km southeast of the summit of Makushin Volcano. The swarm was energetic, with two M>4 events that were widely felt by the population in Dutch Harbor, ~ 15 km west of the epicenters. This is the strongest seismic activity ever recorded at Makushin since instrumental monitoring began in 1996. To date, no eruptive activity or other surface changes have been observed at the volcano in satellite views, webcam images, GPS or InSAR. Seismic swarms close to volcanoes are often associated with the onset of unrest that can lead to eruption. However, determining whether they reflect magmatic rather than tectonic stresses is challenging. Here, we integrate information from space-time patterns of the hypocenters of the swarm earthquakes with their double-couple fault-plane solutions (FPS). We relocate swarm events using double-difference relocation techniques and a 3D velocity model. We find that most of the events cluster into two perpendicular lineaments with NW-SE and SW-NE orientations, but no apparent migration in time towards a preferred fault. On the one hand, the lack of temporal migration (with both faults slipping concurrently), and FPS for M3+ events consistent with regional stresses, seem to indicate a tectonic driving process. On the other hand, FPS for the lower-magnitude earthquakes have 90°-rotated P-axes perpendicular to the regional principal stress orientation, providing strong evidence for dike inflation/magma intrusion. Coulomb stress modeling indicates that the rotated FPS are best explained by an inflating dike to the SW of the swarm epicenters, in a zone of long-term elevated seismicity. This complex overlapping of regional and magmatic stresses is also evident in the statistical analysis of the sequence, which started as a main-shock/aftershock sequence with the first event having the largest magnitude, and evolved into a swarm sequence indicative of a more pronounced role of magmatic processes.</p>

The October 2019 earthquake swarm in the Mineral Mountains, Utah and its relation to the geothermal system

2020 ◽  
Author(s):  
Maria Mesimeri ◽  
Kristine Pankow ◽  
Ben Baker ◽  
Mark Hale
Keyword(s):  
Hot Springs ◽  
Matched Filter ◽  
Earthquake Swarm ◽  
Seismic Network ◽  
Double Difference ◽  
Geothermal System ◽  
Earthquake Catalog ◽  
Earthquake Triggering ◽  
Fault Plane Solutions ◽  
Stress Regime

<p>In October 2019 an earthquake swarm initiated in the Mineral Mountains, Utah near the Roosevelt Hot Springs. The area has been characterized as swarm-genic after the recording of an energetic swarm (1044 microearthquakes, M less than 1.5) during the summer of 1981. This study primarily aims to investigate the spatio-temporal properties of the newly detected earthquake swarm and compare its occurrence to prior seismic activity. The October, 2019 earthquake swarm lasted four days and consists of forty-three shallow earthquakes that were cataloged by the University of Utah Seismograph Stations (UUSS) with magnitudes -0.7 to 1.31. All the events were recorded by a dense local broadband seismic network located around the Frontier Observatory for Research in Geothermal Energy (FORGE) in southcentral Utah, ~10 km west of the activated area. The close proximity of the seismic network along with the density of the seismicity allows us to apply techniques for improving the detection level and earthquake location. To achieve this, we use the earthquakes detected by the UUSS as templates and scan the continuous data for new events by applying a matched filter technique. To perform a detailed spatial analysis of the earthquake swarm and look for migration patterns, we create a high-resolution earthquake catalog using a double difference technique and differential times from both catalog and cross correlation data. To gain insight into the stress regime, we compute fault plane solutions from first motions for individual events and composite focal mechanisms for families of similar events. We further attempt to explore the underlying mechanism by examining the presence of repeating earthquakes comprising the earthquake swarm and their relation to aseismic slip. Such observations may shed insights into the role of fluids and the influence of the high heat flow, due to the geothermal system, on earthquake triggering and migration.</p><p> </p>

scholarly journals Detecting Real Earthquakes Using Artificial Earthquakes: On the Use of Synthetic Waveforms in Matched-Filter Earthquake Detection

2021 ◽  
Author(s):  
Calum Chamberlain ◽  
John Townend
Keyword(s):  
Focal Mechanism ◽  
Matched Filter ◽  
A Priori ◽  
Low Frequency ◽  
Aftershock Sequence ◽  
Filter Method ◽  
Detection Rates ◽  
Earthquake Detection ◽  
American Geophysical ◽  
American Geophysical Union

©2018. American Geophysical Union. All Rights Reserved. Matched-filters are an increasingly popular tool for earthquake detection, but their reliance on a priori knowledge of the targets of interest limits their application to regions with previously documented seismicity. We explore an extension to the matched-filter method to detect earthquakes and low-frequency earthquakes on local to regional scales. We show that it is possible to increase the number of detections compared with standard energy-based methods, with low false-detection rates, using suites of synthetic waveforms as templates. We apply this to a microearthquake swarm and an aftershock sequence, and to detect low-frequency earthquakes. We also explore the sensitivity of detections to the synthetic source's location and focal mechanism. Source-receiver geometry has a first-order control on how sensitive matched-filter detectors are to variations in source location and focal mechanism, and this likely applies to detections made using both synthetic and real templates.

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