scholarly journals Further studies on the 1988 MW 5.9 Saguenay, Quebec, earthquake sequence

2018 ◽  
Vol 55 (10) ◽  
pp. 1115-1128
Author(s):  
Shutian Ma ◽  
Dariush Motazedian ◽  
Maurice Lamontagne
Keyword(s):  
Moment Tensor ◽  
Focal Depth ◽  
P Wave ◽  
Earthquake Sequence ◽  
Eastern Canada ◽  
Nodal Plane ◽  
Rupture Plane ◽  
South Wall ◽  
Seismograph Station ◽  
The Moment

Many small earthquakes occur annually in Eastern Canada, but moderate to strong earthquakes are infrequent. The 25 November 1988 MW 5.9 Saguenay mainshock remains the largest earthquake in the last 80 years in eastern North America. In this article, some aspects of that earthquake sequence were re-analyzed using several modern methods. The regional depth-phase modeling procedure was used to refine the focal depths for the foreshock, the aftershocks, and other MN ≥ 2.5 regional earthquakes. The hypocenters of 10 earthquakes were relocated using hypoDD. The spatial distribution of eight relocated hypocenters defines the rupture plane of the mainshock. The moment tensor for the mainshock was retrieved using three-component long-period surface wave records at station HRV (Harvard seismograph station) with additional constraints from P-wave polarities. One nodal plane is conclusively identified to be close to the rupture plane, and its strike is similar to the trend of the south wall of the Saguenay Graben. Based on the consistency between the strike of the nodal plane and the trend of the Graben, as well as the deep focal depth distribution, we suggest that the Saguenay earthquake sequence is related to the reactivation of one of the faults of the Saguenay Graben.

A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes

1983 ◽  
Vol 73 (2) ◽  
pp. 419-434
Author(s):  
Jeffery S. Barker ◽  
Charles A. Langston
Keyword(s):  
Body Wave ◽  
Moment Tensor ◽  
Normal Fault ◽  
Strike Slip ◽  
Body Waves ◽  
P Wave ◽  
Moment Tensors ◽  
Double Couple ◽  
The Moment ◽  
Mammoth Lakes

abstract Teleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.

Effects of centroid location on determination of earthquake mechanisms using long-period surface waves

1990 ◽  
Vol 80 (5) ◽  
pp. 1205-1231
Author(s):  
Jiajun Zhang ◽  
Thorne Lay
Keyword(s):  
Surface Wave ◽  
Rayleigh Waves ◽  
Body Wave ◽  
Moment Tensor ◽  
Source Location ◽  
P Wave ◽  
Nodal Plane ◽  
Wave Source ◽  
Long Period

Abstract Determination of shallow earthquake source mechanisms by inversion of long-period (150 to 300 sec) Rayleigh waves requires epicentral locations with greater accuracy than that provided by routine source locations of the National Earthquake Information Center (NEIC) and International Seismological Centre (ISC). The effects of epicentral mislocation on such inversions are examined using synthetic calculations as well as actual data for three large Mexican earthquakes. For Rayleigh waves of 150-sec period, an epicentral mislocation of 30 km introduces observed source spectra phase errors of 0.6 radian for stations at opposing azimuths along the source mislocation vector. This is larger than the 0.5-radian azimuthal variation of the phase spectra at the same period for a thrust fault with 15° dip and 24-km depth. The typical landward mislocation of routinely determined epicenters of shallow subduction zone earthquakes causes source moment tensor inversions of long-period Rayleigh waves to predict larger fault dip than indicated by teleseismic P-wave first-motion data. For dip-slip earthquakes, inversions of long-period Rayleigh waves that use an erroneous source location in the down-dip or along-strike directions of a nodal plane, overestimate the strike, dip, and slip of that nodal plane. Inversions of strike-slip earthquakes that utilize an erroneous location along the strike of a nodal plane overestimate the slip of that nodal plane, causing the second nodal plane to dip incorrectly in the direction opposite to the mislocation vector. The effects of epicentral mislocation for earthquakes with 45° dip-slip fault mechanisms are more severe than for events with other fault mechanisms. Existing earth model propagation corrections do not appear to be sufficiently accurate to routinely determine the optimal surface-wave source location without constraints from body-wave information, unless extensive direct path (R1) data are available or empirical path calibrations are performed. However, independent surface-wave and body-wave solutions can be remarkably consistent when the effects of epicentral mislocation are accounted for. This will allow simultaneous unconstrained body-wave and surface-wave inversions to be performed despite the well known difficulties of extracting the complete moment tensor of shallow sources from fundamental modes.

scholarly journals Micro-Crack Mechanism in the Fracture Evolution of Saturated Granite and Enlightenment to the Precursors of Instability

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4595 ◽  
Author(s):  
Longjun Dong ◽  
Yihan Zhang ◽  
Ju Ma
Keyword(s):  
Moment Tensor ◽  
Average Frequency ◽  
Source Model ◽  
P Wave ◽  
Uniaxial Compression Test ◽  
Rock Fracturing ◽  
Fracture Evolution ◽  
Double Couple ◽  
Fracture Size ◽  
The Moment

To explore the potential precursors of rock instability, it is necessary to clarify the mechanism of micro-crack from fracturing to failure, which involves the evolution of fracture size, orientation, source model, and their relationships to the loading. The waveforms of acoustic emission (AE) recorded by the sensor network attached rock sample during laboratory tests provide a data basis for solving these problems, since these observations are directly related to the characteristics of the fracturing sources. Firstly, we investigated the source mechanism, looking at the rise angle and the average frequency (RA-AF) trends during five loading stages in a uniaxial compression test. Results show that the proportion of shear events significantly increases when approaching instability. Secondly, we calculated the moment tensor for each event, considering the uncertainties of P-wave polarity, azimuth, and the takeoff angles of the rays. Moment tensor solutions suggest that there are obviously more crack events than shear events in all loading stages. Moment tensor evolutions confirmed that the decreasing of isotropic component and the increment of double-couple can be used as precursors of rock fracturing development. Considering the limitations of these two methods, it is suggested that we should be concerned more about the proportions of individual failure components and their evolutions over time, instead of absolutely classifying the events into a certain source type.

The ML = 6.8 25 October 2018 Earthquake Zakynthos Island (Ionian Sea) and the evolution of the aftershock sequence one year later

2020 ◽  
Author(s):  
Alexandra Moshou ◽  
Antonios Konstantaras ◽  
Panagiotis Argyrakis ◽  
Nikolaos Sagias
Keyword(s):  
Moment Tensor ◽  
Focal Depth ◽  
Plate Boundary ◽  
Boundary Region ◽  
Aftershock Sequence ◽  
Ionian Sea ◽  
13Th Century ◽  
Hellenic Arc ◽  
The Rich ◽  
The Moment

<p>The area of Zakynthos (Ionian Island) is located at a complex plate boundary region where two tectonic plates (Africa-Nubia and Eurasia) converge, thus forming the western Hellenic Arc. On the midnight of 26<sup>th</sup> October (M<sub>L</sub> = 6.6, 22:54:49 UTC) a very strong earthquake has struck at the eastern part of Zakynthos Island (Ionian Sea, Western Greece). Epicentral coordinates of the earthquake was determined as 37.3410° N, 20.5123° E and a focal depth at 10 km, according to the manual solution of National Observatory of Athens</p><p>(http://bbnet.gein.noa.gr/alerts_manual/2018/10/evman181025225449_info.html).</p><p>This earthquake was strongly felt at the biggest shock was felt as far afield as Naples in western Italy, and in Albania, Libya, and the capital Athens. Nobody was injured by these events but there was significant damage to the local port and a 13th Century island monastery south of Zakynthos.</p><p>A few minutes later (23:09:20, UTC) a second intermediate earthquake with magnitude M<sub>L</sub>=5.1 was followed the first event. The M5+ events of 25 October 2019, as well as the rich aftershock sequence of 10.000+ events with magnitudes 1.0<ML<4.9 of the 12 following months have been relocated using the double – difference algorithm HYPODD.</p><p>For the aftershocks with 3.7<M<sub>L</sub><6.6 we applied the moment tensor inversion to determine the activation of the faulting type, the Seismic Moment (M<sub>0</sub>) and the Moment Magnitude (M<sub>w</sub>). For this purpose, 3–component broadband seismological data from the Hellenic Unified Seismological Network (HUSN) at epicentral distances less than 3˚ were selected and analyzed. The preparation of the data, includes the deconvolution of instrument response, following the velocity was integrated to displacement and finally the horizontal components rotated to radial and transverse. All the focal mechanisms were compared with those from other institutes and they are in agreement. The second part of this study refers to the calculation of the stress tensor using the STRESSINVERSE package by Václav Vavryčuk. The final part of this study includes an extensive kinematic analysis of geodetic data from local GNSS permanent station to further examine the dynamic displacement.</p><p>References:</p><ol><li>Athanassios Ganas, Pierre Briole, George Bozionelos, Panagiotis Elias, Sotiris Valkaniotis, Varvara Tsironi, Alexandra Moshou and Nikoletta Andritsou, 2019. The October 25, 2018 M6.7 Zakynthos earthquake sequence (Ionian Sea, Greece): fault modeling from seismic and GNSS data and implications for seismic strain release along the western Hellenic Arc, 15th, Sp. Pub. 7, Ext. Abs. GSG2019 – 324</li> <li>Konstantaras A.J. Classification of distinct seismic regions and regional temporal modelling of seismicity in the vicinity of the Hellenic seismic arc. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. 6 (4), 1857-1863, 2012.</li> <li>Gerassimos A. Papadopoulos, Vassilios K. Karastathis, Ioannis Koukouvelas, Maria Sachpazi, Ioannis Baskoutas, Gerassimos Chouliaras, Apostolos Agalos, Eleni Daskalaki, George Minadakis, Alexandra Moshou, Aggelos Mouzakiotis, Katerina Orfanogiannaki, Antonia Papageorgiou, Dimitrios Spanos, Ioanna Triantafyllou. The Cephalonia, Ionian Sea (Greece), sequence of strong earthquakes of January – February 2014: A first report, Research in Geophysics 2014; 4:5441</li> </ol>

The major (Mw=7.0) earthquake of 30th October 2020 north Samos Island, Greece: Analysis of seismological and geodetic data 

2021 ◽  
Author(s):  
Alexandra Moshou ◽  
Antonios Konstantaras ◽  
Panagiotis Argyrakis
Keyword(s):  
Service Providers ◽  
Expert Knowledge ◽  
Moment Tensor ◽  
Focal Depth ◽  
Stress Transfer ◽  
Seismic Zone ◽  
Western Turkey ◽  
Tsunami Early Warning ◽  
The North ◽  
The Moment

<p>On 30th October 2020, at 11.51 (UTC), a very strong earthquake of magnitude M<sub>w </sub>= 7.0 struck north of the Greek island of Samos in the Aegean coast of Turkey, south of Izmir. The epicentre was determined 17km north of Samos, in the Gulf of Ephesus and was felt in many parts of Greece and western Turkey. The geographical coordinates as calculated of the manual analysis of the National Observatory of Athens (http://bbnet.gein.noa.gr/Events/2020/10/noa2020vipzs_info.html) was determined as  φ= 37.9001⁰N, λ=26.8167⁰E at a focal depth at 11.8km. The earthquake triggered a tsunami that flooded the coastal district of Seferihisar (Turkey), Cesme, Izmir and the port of Samos (Greece). In the next 8 minutes after the detection of the earthquake, tsunami bulletins were issued to national focal points by the Tsunami Service Providers accredited by UNESCO’s IOC Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas (ICG/NEAMTWS). Greece and Turkey were put on Tsunami Watch (highest level of alert). In Seferishar the tsunami swept away many boats in the marina and the water level reached 1.5 meters causing damage to shops.</p><p>Three hours later, 15:14 (UTC) a second strong event (M<sub>w </sub>= 5.3) occurred in the same region some kilometres south of the main earthquake (φ=37.8223⁰N,λ=26.8652⁰E, http://bbnet.gein.noa.gr/Events/2020/10/noa2020viwsi_info.html). By the end of the same day that the earthquake took place, there were 65 aftershocks while a total of 576 aftershocks up to 31/12 with magnitude greater than 1.0. For the aftershocks with 3.7<M<sub>L</sub><7.0 we applied the moment tensor inversion to determine the focal mechanism, the Seismic Moment (M<sub>0</sub>) and the Moment Magnitude (Mw). For this purpose, 3–component broadband seismological data from the Hellenic Unified Seismological Network (HUSN) at epicentral distances less than 3˚ were selected and analysed. The preparation of the data, includes the deconvolution of instrument response, following the velocity was integrated to displacement and finally the horizontal components rotated to radial and transverse. Finally, an extensive kinematic analysis from data provided by two private sector companies networks was done.</p><p>References:</p><p>Athanassios Ganas, Penelope Kourkouli, Pierre Briole, Alexandra Moshou, Panagiotis Elias and Isaak Parcharidis. Coseismic Displacements from Moderate-Size Earthquakes Mapped by Sentinel-1 Differential Interferometry: The Case of February 2017 Gulpinar Earthquake Sequence (Biga Peninsula, Turkey), Remote Sensing, 2018, pp. 237 – 248</p><p>Athanassios Ganas, Zafeiria Roumelioti, Vassilios Karastathis, Konstantinos Chousianitis, Alexandra Moshou, Evangelos Mouzakiotis. The Lemnos 8 January 2013 (Mw=5.7) earthquake: fault slip, aftershock properties and static stress transfer modeling in the north Aegean Sea J Seismol (2014) 18:433–455 DOI 10.1007/s10950-014-9418-3</p><p>Konstantaras A. Deep Learning and Parallel Processing Spatio-Temporal Clustering Unveil New Ionian Distinct Seismic Zone. Informatics, 7(4), 39, 2020</p><p>KONSTANTARAS, A. Expert knowledge-based algorithm for the dynamic discrimination of interactive natural clusters. Earth Science Informatics 9, (2016), 95-100</p>

Fault parameters of the St. Elias, Alaska, earthquake of February 28, 1979

1980 ◽  
Vol 70 (5) ◽  
pp. 1651-1660
Author(s):  
H. S. Hasegawa ◽  
J. C. Lahr ◽  
C. D. Stephens
Keyword(s):  
Main Shock ◽  
Focal Depth ◽  
P Wave ◽  
Large Magnitude ◽  
Aftershock Activity ◽  
Nodal Plane ◽  
Fault Parameters ◽  
Fault Length ◽  
Interplate Earthquakes ◽  
Alaska Earthquake

abstract Fault parameters of the Ms 7.1 St. Elias, Alaska, earthquake of February 28, 1979, are determined from an analysis of P-wave first motions, fundamental-mode surface waves, and aftershock data. The preferred P-wave nodal plane has a shallow (12°) angle of dip and indicates underthrusting in a northerly (N13°W) direction, which is also close to the azimuth (N8°W) of the deviatoric compression (P) vector. Aftershock activity during the 24-hr interval immediately following the main shock extends over an area of 3200 km2, which is taken to represent the fault area of the main shock. Because aftershock activity outlines a fault area with nonrectangular geometry, fault length (50 to 80 km) and width (50 to 65 km) are not well defined. Estimates of focal depth from aftershock activity fall in the range 10 to 20 km, which surface-wave analysis is unable to restrict further. For the main shock, seismic moment, Mo, is 2.5 × 1027 dyne-cm (0.25 × 1021 N.m) and average dislocation, 2 meters. Average rupture velocity falls in the range 2.5 to 3 km/sec. Apparent stress, ησ, is 5 bars (0.5 MPa) and stress drop, Δσ, 35 bars (3.5 MPa). These values are considered typical of large-magnitude interplate earthquakes.

Focal depth distribution of the 1982 Miramichi earthquake sequence determined by modelling depth phases

2017 ◽  
Vol 54 (4) ◽  
pp. 359-369 ◽  
Author(s):  
Shutian Ma ◽  
Dariush Motazedian
Keyword(s):  
New Brunswick ◽  
New England ◽  
Rayleigh Waves ◽  
Depth Distribution ◽  
Body Wave ◽  
Focal Depth ◽  
Earthquake Sequence ◽  
Depth Range ◽  
Eastern Canada ◽  
Body Wave Magnitude

On 9 January 1982, in the Miramichi region of New Brunswick, Canada, an earthquake with body-wave magnitude (mb) 5.7 occurred, and extensive aftershocks followed. The mainshock was felt throughout Eastern Canada and New England, USA. The mainshock and several principal aftershocks were digitally recorded worldwide, but smaller aftershocks were digitally recorded only at regional stations. Digital stations were not yet popular in 1982; therefore, available regional digital waveform records for modelling are very limited. Fortunately, two Eastern Canada Telemetered Network (ECTN) stations, EBN and KLN, produced excellent waveform records for most of the aftershocks until their closure at the end of 1990. The waveform records can be retrieved from the archive database at the Geological Survey of Canada (GSC). Since EBN had clear sPmP records of the larger aftershocks (with magnitude mN ≥ 2.8), we were able to determine focal depths for these larger events. Most of the focal depth solutions for the 113 larger aftershocks were within a depth range of 3–6 km. The majority of the depths were at about 4.5 km. Some aftershocks had depths of about 1–2 km. The focal depth solutions for the shallow events were confirmed by the existence of prominent crustal Rayleigh waves. As the records for the foreshock and the mainshock at EBN were not available, we used the records at station LMN for the foreshock and a teleseismic depth phase for the mainshock. The teleseismic depth phase comparison shows that the mainshock and its three principal aftershocks migrated from a depth of about 7 km to near the Earth’s surface.

Further testing of the bedding-plane-slip model for hydraulic-fracture opening using moment-tensor inversions

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. KS159-KS168 ◽  
Author(s):  
Yunhui Tan ◽  
Terry Engelder
Keyword(s):  
Hydraulic Fracture ◽  
Moment Tensor ◽  
P Wave ◽  
Hydraulic Fractures ◽  
Washington County ◽  
Gas Shale ◽  
Nodal Plane ◽  
Moment Tensors ◽  
Bedding Planes ◽  
Microseismic Events

Moment tensors are calculated by using the P-wave first motion peak amplitudes of 59 microseismic events with high signal-to-noise ratio. These events are from a surface microseismic data set gathered during hydraulic-fracture stimulation of the Marcellus gas shale in Washington County, Pennsylvania, USA. The majority of these 59 events have a horizontal nodal plane ([Formula: see text] a few degrees) characteristic of a dip-slip/horizontal-slip moment tensor. If the horizontal nodal plane is an auxiliary, the vertical nodal plane has a pure dip-slip motion, which is inconsistent with the opening motion for vertical hydraulic fractures that enables proppant loading. This points to slip on horizontal nodal planes with the auxiliary vertical nodal planes aligned with the local maximum horizontal stress orientation as indicated by drilling-induced fractures in nearby vertical wells. These 59 microseismic events are caused by slip on horizontal mechanical discontinuities such as bedding planes during the opening of vertical hydraulic fractures, a model first proposed by research teams headed by Rutledge and Eisner, respectively. During several stimulation stages in the Washington County Marcellus gas shale, a pattern of opposite slip direction develops within “double lineaments” of microseismic clouds. This suggests that fracking fluid is not only able to move in the direction of fracture propagation, but it can also spread sideways into previously unstimulated rock. A secondary microseismic cloud consistently initiates at approximately 133 m (400 ft) from the position opposite the central perforation toward the unstimulated heel of the horizontal wells. From these moment tensors, we have concluded that microseismic focal mechanisms with horizontal nodal planes are direct evidence of the presence of treatment fluid in open hydraulic fractures.

The North Gower, Ontario, Earthquake of 11 October 1983: Focal Mechanism and Aftershocks

1987 ◽  
Vol 58 (3) ◽  
pp. 65-72 ◽  
Author(s):  
Rutger Wahlstreöm
Keyword(s):  
Focal Mechanism ◽  
Fault Plane ◽  
Focal Depth ◽  
P Wave ◽  
Focal Mechanism Solution ◽  
Nodal Plane ◽  
Fault Plane Solutions ◽  
Stress Regime ◽  
Motion Data ◽  
The North

Abstract An earthquake near Ottawa (45.20°N, 75.75°W, focal depth 12 km) of unusually large size for the region's seisrhicity (mb(Lg) = 4.1) provided good P-wave first-motion data for a focal-mechanism solution. The maximum intensity was V(MM) and the area of perceptibility in Canada about 80,000 km2. The first and largest recorded aftershock occurred nine minutes after the main shock with magnitude mb(Lg) = 1.7. Two further small aftershocks ware recorded by a field network. The mechanism is thrust faulting with a predominantly horizontal pressure axis trending 154°. Thrust mechanisms have been found for other earthquakes in southeastern Canada and the northeastern U.S., but orientations of their stress axes are different, and so the North Gower earthquake may reflect a local and not a regional stress field. The nodal planes have strike 71°, dip 75°, and strike 221°, dip 17°. The spatial distribution of aftershocks suggests the gently-dipping nodal plane could be the fault plane. There is uncertainty about the seismotectonics of the region, and the orientation of neither nodal plane correlates with known geological features. More earthquake fault-plane solutions are required to interpret the seismotectonics and the stress regime.

On an improved method to obtain the moment tensor and depth of earthquakes from the amplitude spectrum of Rayleigh waves

1983 ◽  
Vol 73 (6A) ◽  
pp. 1513-1526
Author(s):  
Barbara Romanowicz ◽  
Gerardo Suárez
Keyword(s):  
Rayleigh Waves ◽  
Variance Reduction ◽  
Body Wave ◽  
Moment Tensor ◽  
Amplitude Spectrum ◽  
Focal Depth ◽  
Vertical Component ◽  
Tien Shan ◽  
Period Range ◽  
The Moment

Abstract A new method is presented to invert for the moment tensor and depth using the amplitude spectra of vertical-component Rayleigh waves in the period range 20 to 100 sec. The technique follows a similar approach to that suggested by Romanowicz (1982a) to invert for the moment tensor from the complex spectra of Rayleigh waves and presents some distinct advantages to the method proposed originally by Mendiguren (1977). It eliminates some biases and errors in the data arising, for example, from inaccurate propagation corrections. Furthermore, it is substantially faster computationally and permits us to study independently the variance reduction as a function of depth of each of the momenttensor elements, resulting in better focal depth resolution. The method is applied to three earthquakes in the Tien Shan Mountains of Central Asia, the Eastern Cordillera of Peru, and the Gibbs Transform fault in the North Atlantic. In all three cases, the results of the moment-tensor inversion agree with those determined using long-period body-wave modeling.

Sign in / Sign up

Export Citation Format

Share Document