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.

Anomalous microtilt preceding a local earthquake

1971 ◽  
Vol 61 (6) ◽  
pp. 1801-1809 ◽  
Author(s):  
M. D. Wood ◽  
R. V. Allen
Keyword(s):  
San Francisco ◽  
Strong Correlation ◽  
Earthquake Swarm ◽  
Time Interval ◽  
Azimuthal Correlation ◽  
Short Term ◽  
Epicentral Area ◽  
Local Earthquake ◽  
Tilt Change

abstract The three largest earthquakes to occur within 50 km of San Francisco during 1970 were centered near the community of Danville, California, and spanned a time interval of 50 sec starting on June 12, at 0330 hr GMT. These earthquakes were greater than magnitude 4.0 and were part of a shallow, tightly-clustered earthquake swarm that persisted for approximately 2 months starting in mid-May 1970. During the same period of time, continuous tilt at tidal sensitivity (10−8 radian) was being recorded in two vaults at distances of 25 and 45 km west of the epicentral area. Two types of anomalous tilting preceded the principal events: (1) a long-term (1-month) constant tilt rate of 8 × 10−10 radian/hr that was recorded by both tilt stations and (2) a short-term (1-day) accelerated micro-tilt change which occurred just prior to the events and was most pronounced on the station closest to the epicentral area. Neither type of anomaly was recognized in the post-Danville record. The lack of a strong correlation with meteorological phenomena to account for the long-term coherency between two tilt stations of 25-km separation and the apparent azimuthal correlation of the Berkeley residual tilt vector with the earthquake epicenters suggests that the anomalous tilt preceding the Danville events were tectonic.

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.

scholarly journals An intraplate slow earthquake observed by a dense GPS network in Hokkaido, northernmost Japan

2014 ◽  
Vol 200 (1) ◽  
pp. 144-148 ◽  
Author(s):  
Mako Ohzono ◽  
Hiroaki Takahashi ◽  
Masayoshi Ichiyanagi
Keyword(s):  
Subduction Zones ◽  
Earthquake Swarm ◽  
Tectonic Activity ◽  
Maximum Magnitude ◽  
Slow Slip ◽  
Localized Deformation ◽  
Slow Earthquake ◽  
Magnitude Scaling ◽  
Duration Magnitude ◽  
Slow Earthquakes

Abstract An intraplate slow earthquake was detected in northernmost Hokkaido, Japan, by a dense network of the global navigation satellite system. Transient abnormal acceleration of <12 mm was observed during the period 2012 July to 2013 January (∼5.5 months) at several sites. The spatial displacement distribution suggests that a localized tectonic event caused localized deformation. Estimated fault parameter indicates very shallow-dip reverse faulting in the uppermost crust, with a total seismic moment of 1.75E + 17 N m (Mw 5.4). This fault geometry is probably consistent with detachment structure indicated by geological studies. A simultaneous earthquake swarm with the maximum magnitude M4.1 suggests a possibility that the slow slip triggered the seismic activity for unknown reasons. This slow earthquake is slower than its moment would indicate, with a duration–magnitude scaling relationship unlike either regular earthquakes or subduction slow slip events. This result indicates that even if the area is under different physical property from subduction zones, slow earthquake can occur by some causes. Slow earthquakes exist in remote regions away from subduction zones and might play an important role in strain release and tectonic activity.

Coseismic fluid-pressure response estimated from prediction-error filtering of tidal-band loading

1999 ◽  
Vol 89 (6) ◽  
pp. 1439-1446 ◽  
Author(s):  
Timothy L. Masterlark ◽  
Herbert F. Wang ◽  
Lung S. Chan ◽  
Che Yongtai
Keyword(s):  
Prediction Error ◽  
Transfer Functions ◽  
Earthquake Swarm ◽  
Fluid Pressure ◽  
Pressure Response ◽  
Water Levels ◽  
Ocean Tide ◽  
Dislocation Model ◽  
Ocean Tide Loading ◽  
Forcing Function

Abstract A methodology combining prediction-error filters (PEFs) and transfer functions was developed to identify the quasi-static fluid-pressure response observed in wells due to coseismic strain. Water levels in confined aquifers respond to long-term and seasonal trends, recharge events, barometric and ocean tide loading, tidal strain, and tectonic strain. Low-frequency features can be neglected from the quasistatic coseismic response estimation. Transfer functions were constructed to deconvolve the fluid-pressure response due to measured barometric loading. Because direct tidal strain and ocean tide loading measurements are rarely available, theoretical tidal loading is often calculated from astronomical data. However, the calculations are subject to many assumptions. Because tidal driving processes are cyclic, PEFs are a natural choice for removing the fluid-pressure response without assuming a theoretical forcing function in the tidal band. The method was applied to hourly fluid pressure data collected over a 3-year period from two wells in the villages of Gaocun and Tayuan, China. Results of this analysis yielded coseismic fluid pressure heads of −1.6 × 10−2 and +7.6 × 10−2 m for the respective wells in response to the Datong-Yanggao earthquake swarm mainshock (Ms 6.1), 18-24 October 1989. Epicentral distances to the wells were about 200 km. The coseismic fluid-pressure response for each well was also predicted from dislocation model strain scaled by material-dependent volumetric strain sensitivity parameters. These parameters were determined from the static confined response to O1 and M2 earth-tide strain constituents. The predicted response was −2.9 × 10−3 m for the Gaocun well and +2.1 × 10−3 m for the Tayuan well. Although predicted and observed response phases were consistent, both predictions underestimated observed response amplitudes, as has been true in other reported instances.

Wildlife Population Estimates by Census and Distance Measuring Techniques

2021 ◽  
pp. 281-292
Author(s):  
Peter A. Henderson
Keyword(s):  
Fourier Series ◽  
Sampling Methods ◽  
Survey Methods ◽  
Distance Sampling ◽  
Population Estimates ◽  
Nearest Neighbour ◽  
Wildlife Population ◽  
Measuring Techniques ◽  
Line Survey ◽  
Distance Measuring

Methodologies based on counting the number of sightings to estimate are described. These techniques are particularly useful for large or easily seen animals such as birds, large grassland mammals, whales, crocodilians, and large, active insects such as butterflies. Point and line survey methods are described. Distance sampling methods, including Fourier series estimators, are presented, and R code listings to undertake the computations presented. Plotless density estimators are described based on nearest-neighbour, and closest-individual measurements are described.

Laser Distance-Measuring Techniques

1977 ◽  
Vol 5 (1) ◽  
pp. 357-369 ◽  
Author(s):  
J Levine
Keyword(s):  
Measuring Techniques ◽  
Distance Measuring

scholarly journals Crustal deformations in the epicentral area of the West Bohemia 2008 earthquake swarm in central Europe

2012 ◽  
Vol 117 (B7) ◽  
pp. n/a-n/a ◽  
Author(s):  
Vladimír Schenk ◽  
Zdeňka Schenková ◽  
Zuzana Jechumtálová ◽  
Richard Pichl
Keyword(s):  
Central Europe ◽  
Earthquake Swarm ◽  
The West ◽  
Epicentral Area ◽  
West Bohemia

Joint hypocentral determination and the detection of low-velocity anomalies. An example from the Phlegraean Fields earthquakes

1990 ◽  
Vol 80 (1) ◽  
pp. 129-139 ◽  
Author(s):  
Jose Pujol ◽  
Richard Aster
Keyword(s):  
Earthquake Swarm ◽  
P Wave ◽  
S Wave ◽  
Time Data ◽  
Low Velocity ◽  
Data Set ◽  
Epicentral Area ◽  
Velocity Inversion ◽  
Phlegraean Fields ◽  
Velocity Anomalies

Abstract Arrival time data from the Phlegraean Fields (Italy) earthquake swarm recorded by the University of Wisconsin array in 1983 to 1984 were reanalyzed using a joint hypocentral determination (JHD) technique. The P- and S-wave station corrections computed as part of the JHD analysis show a circular pattern of central positive values surrounded by negative values whose magnitudes increase with distance from the center of the pattern. This center roughly coincides with the point of the maximum uplift (almost 2 m) associated with the swarm. Corrections range from −0.85 to 0.10 sec for P-wave arrivals and from −1.09 to 0.70 sec for S-wave arrivals. We interpret these patterns of corrections as caused by a localized low-velocity anomaly in the epicentral area, which agrees with the results of a previous 3-D velocity inversion of the same data set. The relocated (JHD) epicenters show less scatter than the epicenters obtained in the velocity inversion, and move more of the seismic activity to the vicinity of the only presently active fumarolic feature. The capability of the JHD technique to detect low-velocity anomalies and at the same time to give reliable locations, particularly epicenters, was verified using synthetic data generated for a 3-D velocity model roughly resembling the model obtained by velocity inversion.

scholarly journals The 2020 M6.4 Jiashi Earthquake: An Event that Occurred Under the Décollement on the Kaping Fold-and-Thrust Belt in the Southwestern Tien Shan Mountains, China

2021 ◽  
Vol 9 ◽  
Author(s):  
Qi Yao ◽  
Wen Yang ◽  
Xianghua Jiang ◽  
Yanshuang Guo ◽  
Jie Liu ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Earthquake Swarm ◽  
Tien Shan ◽  
Thrust Belt ◽  
Seismic Profiles ◽  
Seismogenic Structure ◽  
Epicentral Area ◽  
Velocity Models ◽  
Fold And Thrust Belt ◽  
Tarim Craton

The 2020 Jiashi M6.4 earthquake occurred in the Kaping fold-and-thrust belt, a major south-verging active thin-skin system in the southwestern Chinese Tien Shan Mountain, north of the Tarim Basin. Within 50 km from the epicentral area, seismic hazard is high, as suggested by the occurrence of the 1902 Mw 7.7 Artux (Kashgar) earthquake and 1997 Jiashi strong earthquake swarm. The seismogenic structure responsible for the 2020 event is not well constrained and is a subject of debate. We relocated the 2020 Jiashi earthquake sequence and assessed the relocation uncertainties, using eight seismic velocity models and based on detailed local and regional subcrustal structures from seismic profiles. Then we compared the temporal variation in the Gutenberg–Richter b-values of the 2020 sequence with those of the 1997, 1998, and 2003 earthquake sequences. Our results show that most events cluster at depths greater than 10 km, suggesting that the events most likely occurred beneath the décollement and inside the Tarim Craton. The spatiotemporal evolution of the sequence suggests that two groups of structures at depth were involved in the 2020 sequences: NW–SE-trending lateral strike-slip faults and E–W-trending reverse faults. The b-values of the 2020 sequence exhibits relatively stable temporal evolution, unlike those of the multi-shock sequence that occurred inside the Tarim Craton. It indicates that the 2020 sequence perhaps was influenced by the stress interaction with the 10 km thick overlying strata. Our study provides a new perspective on the seismogenic structure of the earthquakes that occurred because of reactivation of ancient structures developed in a stable craton.

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