Earthquakes along the Northwestern Boundary of the Labrador Sea

1992 ◽  
Vol 63 (4) ◽  
pp. 587-602 ◽  
Author(s):  
Allison L. Bent ◽  
Henry S. Hasegawa
Keyword(s):  
Hot Spot ◽  
Source Parameters ◽  
Normal Fault ◽  
Gravity Anomalies ◽  
Tectonic Stress ◽  
Passive Margin ◽  
Labrador Sea ◽  
Spreading Ridge ◽  
Fault Plane Solutions ◽  
Thrust Faulting

Abstract As in much of northeastern Canada, earthquakes in the Labrador Sea occur predominantly along the passive margin. Geologically and geophysically, this region is complex and consists of an extinct spreading ridge and transform faults, both oceanic and continental crust, a possible hot spot trace, and magnetic and gravity anomalies. We have studied five recent earthquakes in the magnitude 4.5 to 5.5 range to determine their source properties and to better understand how they fit into the seismotectonic framework of the region. A combination of body and surface wave analysis techniques were used to determine the source parameters. LS69, LS89 and PB89 were well recorded teleseismically, and thus their source properties are better constrained than those for LS86 and LS87, for which only a few teleseismic records were available and whose source parameters were determined more from first motions than by modeling. The two events (LS69, LS89) that occurred near the intersection of the extinct spreading ridge (and associated transform) and Mesozoic rifted margin are noteworthy in that the former is of the thrust-fault and the latter of the normal-fault type. Local structure and possibly post-glacial rebound could be the causative factors for the occurrence of normal and thrust faulting in the same area. The two events (LS86, LS87) that occurred along the continent ocean transition zone have fairly similar fault-plane solutions, and are both thrust-faulting events. The fifth event (PB89), which occurred in Payne Bay, is also a thrust-faulting event and could be associated with the Ungava Transform fault to the northeast, or the Cape Smith fold belt to the northwest. The focal depths of all five events lie between 10 and 15 km, and may be dominated by thermal effects. The observation that the deviatoric compression axis of all five earthquakes lies in the northwest (or equivalently in the southeast) quadrant is consistent with recent modeling efforts of the tectonic stress field in this region.

scholarly journals Evidence for Basement Reactivation during the Opening of the Labrador Sea from the Makkovik Province, Labrador, Canada: Insights from Field Data and Numerical Models

Geosciences ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 308 ◽  
Author(s):  
Alexander Peace ◽  
Edward Dempsey ◽  
Christian Schiffer ◽  
J. Welford ◽  
Ken McCaffrey ◽  
...  
Keyword(s):  
Stress Field ◽  
Numerical Models ◽  
Passive Margin ◽  
Labrador Sea ◽  
Spreading Ridge ◽  
Stress Inversion ◽  
Eastern Canada ◽  
Stress Regime ◽  
General Direction ◽  
Continental Breakup

The onshore exposures adjacent to modern, offshore passive continental margins may preserve evidence of deformation from the pre-, syn-, and post-rift phases of continental breakup that allow us to investigate the processes associated with and controlling rifting and breakup. Here, we characterize onshore brittle deformation and pre-rift basement metamorphic mineral fabric from onshore Labrador in Eastern Canada in the Palaeoproterozoic Aillik Domain of the Makkovik Province. Stress inversion (1) was applied to these data and then compared to (2) numerical models of hybrid slip and dilation tendency, (3) independent calculations of the regional geopotential stress field, and (4) analyses of palaeo-stress in proximal regions from previous work. The stress inversion shows well-constrained extensional deformation perpendicular to the passive margin, likely related to pre-breakup rifting in the proto-Labrador Sea. Hybrid slip and dilatation analysis indicates that inherited basement structures were likely oriented in a favorable orientation to be reactivated during rifting. Reconstructed geopotential stresses illuminate changes of the ambient stress field over time and confirm the present paleo-stress estimates. The new results and numerical models provide a consistent picture of the late Mesozoic-Cenozoic lithospheric stress field evolution in the Labrador Sea region. The proto-Labrador Sea region was characterized by a persistent E–W (coast-perpendicular) extensional stress regime, which we interpret as the pre-breakup continental rifting that finally led to continental breakup. Later, the ridge push of the Labrador Sea spreading ridge maintained this general direction of extension. We see indications for anti-clockwise rotation of the direction of extension along some of the passive margins. However, extreme persistent N–S-oriented extension as indicated by studies further north in West Greenland cannot be confirmed.

scholarly journals Seismogenesis in Central Apennines, Italy: an integrated analysis of minor earthquake sequences and structural data in the Amatrice-Campotosto area

2009 ◽  
Vol 47 (6) ◽  
Author(s):  
P. Boncio ◽  
G. Lavecchia ◽  
G. Milana ◽  
B. Rozzi
Keyword(s):  
Late Quaternary ◽  
Central Italy ◽  
Normal Fault ◽  
Structural Data ◽  
Integrated Analysis ◽  
Fault Plane Solutions ◽  
Small Magnitude ◽  
Fault Surface ◽  
Displacement Profile ◽  
Earthquake Sequences

We present a seismotectonic study of the Amatrice-Campotosto area (Central Italy) based on an integrated analysis of minor earthquake sequences, geological data and crustal rheology. The area has been affected by three small-magnitude seismic sequences: August 1992 (M=3.9), June 1994 (M=3.7) and October 1996 (M=4.0). The hypocentral locations and fault plane solutions of the 1996 sequence are based on original data; the seismological features of the 1992 and 1994 sequences are summarised from literature. The active WSWdipping Mt. Gorzano normal fault is interpreted as the common seismogenic structure for the three analysed sequences. The mean state of stress obtained by inversion of focal mechanisms (WSW-ENE-trending deviatoric tension) is comparable to that responsible for finite Quaternary displacement, showing that the stress field has not changed since the onset of extensional tectonics. Available morphotectonic data integrated with original structural data show that the Mt. Gorzano Fault extends for ~28 km along strike. The along-strike displacement profile is typical of an isolated fault, without significant internal segmentation. The strong evidence of late Quaternary activity in the southern part of the fault (with lower displacement gradient) is explained in this work in terms of displacement profile readjustment within a fault unable to grow further laterally. The depth distribution of seismicity and the crustal rheology yield a thickness of ~15 km for the brittle layer. An area of ~530 km2 is estimated for the entire Mt. Gorzano Fault surface. In historical times, the northern portion of the fault was probably activated during the 1639 Amatrice earthquake (I = X, M~ 6.3), but this is not the largest event we expect on the fault. We propose that a large earthquake might activate the entire 28 km long Mt. Gorzano Fault, with an expected Mmax up to 6.7.

Contemporary deformation and earthquake hazard of the Capital Circle of China inferred from GPS Measurements

2021 ◽  
Author(s):  
Shaogang Wei ◽  
Xiwei Xu ◽  
Tuo Shen ◽  
Xiaoqiong Lei
Keyword(s):  
High Risk ◽  
Earthquake Hazard ◽  
Historical Earthquakes ◽  
Tectonic Stress ◽  
Middle Part ◽  
Earthquake Hazards ◽  
Seismic Belt ◽  
Fault Plane Solutions ◽  
The North ◽  
Recent Earthquakes

<p>The Capital Circle (CC) is a region with high risk of great damaging earthquake hazards. In our present study, by using a subset of rigorously GPS data around the North China Plain (NCP), med-small recent earthquakes data and focal mechanism of high earthquakes data covering its surrounding regions, the following major conclusions have been reached: (a) Driven by the deformation force associated with both eastward and westward motion, with respect to the NCP, of the rigid South China and the rigid Amurian block, widespread sinistral shear appear over the NCP, which results in clusters of parallel NNE-trending faults with predominant right-lateral strike-slips via bookshelf faulting within the interior of the NCP. (b) Fault plane solutions of recent earthquakes show that tectonic stress field in the NCP demonstrate overwhelming NE-ENE direction of the maximum horizontal principal stress, and that almost all great historical earthquakes in the NCP occurred along the NWW-trending Zhangjiakou-Bohai seismic belt and the NNE-trending Tangshan-Hejian-Cixian seismic belt. Additionally, We propose a simple conceptual model for inter-seismic deformation associated with the Capital Circle, which might suggest that two seismic gaps are located on the middle part of Tangshan-Hejian-Cixian fault seismic belt (Tianjin-Hejian segment) and the northeast part of Tanlu seismic belt (Anqiu segment), and constitute as, in our opinion, high risk areas prone to great earthquakes.</p>

Physical modeling of the formation of the microcontinent Jan Mayen

2020 ◽  
Author(s):  
Grigory Agranov ◽  
Eugene Dubinin ◽  
Andrey Grokholsky ◽  
Anna Makushkina
Keyword(s):  
Physical Simulation ◽  
Hot Spot ◽  
Magnetic Anomalies ◽  
Local Heat ◽  
Spreading Ridge ◽  
Spreading Axis ◽  
The North ◽  
The World ◽  
Initial Geometry ◽  
Northern Branch

<p>The split between the North American and Eurasian plates began in the Late Pleistocene - Early Eocene (58-60 million years). As the stretching took place, overlapping rift cracks formed. With further evolution, the crack that came from the north fully formed, while the south at that time died out, forming the axis of paleospreading (early Ypresian Age, 49.7 Ma). A hot spot was already functioning near Greenland at that time. In the Priabonian Age (33.1 million years), the hot spot ended under the axis of paleospreading. As a result, the spreading axis jumped (Peron-Pinvidic et al., 2012) creating the Jan Mine main microcontinent and the Kolbeinsain spreading ridge. In addition, the northern branch of the spreading ridge died out and the Aegir paleospreading ridge formed. These raises a number of questions arise:</p><p>-What is the mechanism for the separation of the Jan Mine continental block?</p><p>-Why did the spreading axis jumped and the Aegir Ridge wither away?</p><p>-What is the effect of the Icelandic hot spot on microblock formation?</p><p>-Are there similar structures in the world formed through a similar mechanism?</p><p>To answer these questions, a physical simulation was performed. Some of these issues were considered in (Muller et al., 2001, Gaina et al., 2003, Mjelde et al., 2008, Mjelde, Faleide, 2009).</p><p>Modelling was based on the initial geometry of rift cracks, known oldest magnetic anomalies and existing reconstructions. It showed two possibilities for the formation of the Jan Mayen microcontinent.</p><p>The first model is associated with parallel or oblique strike of rift cracks, the oncoming movement of which leads to their overlap, isolation of the microcontinental block, which experienced deformation and rotation.</p><p>The second model is associated with the presence of a local heat source (hot spot), the influence of which led to a jump of one branch of the rift towards the hot spot, and to the generation of a significant amount of magmatic material, which could significantly change the initial continental structure of the microblock. The second method, which combines the influence of the overlap zone and the hot spot, showed the best correlation with natural structures.</p>

Structural framework and regional significance of the Northandean Cretaceous subduction cycle

2020 ◽  
Author(s):  
Andreas Kammer ◽  
Michael Avila
Keyword(s):  
Subduction Zones ◽  
Normal Fault ◽  
Large Igneous Province ◽  
Mantle Flow ◽  
Spreading Ridge ◽  
Forearc Basin ◽  
Plate Convergence ◽  
Continental Plate ◽  
Igneous Province ◽  
Cretaceous Subduction

<p>The Northandean plate margin underwent a fundamental change in its structural configuration during a Cretaceous subduction cycle, as evidenced by the formation and accretion of a province of basic igneous arc rocks that gave rise to the basement of an Northandean Western Cordillera. Further north, this igneous terrane links to the Caribbean Large Igneous Province and has been associated, with respect to its origin, to an actively spreading ridge of the Farallon plate, implying a far-travelled origin with respect to Southamerica and calling for the existence of giant strike-slip faults. We challenge this allochthonous scenario by an alternative option of a forearc origin, invoking the possibility of a forearc opening by the forcing of a toroidal mantle flow at the northern end of the Andean trench, which would have introduced mantle material from the Pacific into the Andean realm through a Central American gap. Support for such an opening mode of a forearc basin comes from extensional tectonics, that accompanied the emplacement of the basic arc units and a concomitant subduction of the extrusive basic units at the inner border of this postulated forearc basin. This intraplate subduction comprises a distinct three-partite evolution: (I) Convergence first became manifest by the reactivation of a normal fault located within the supposed forearc basin and inboard of an inherited Triassic-Jurassic suture, but still failed at a crustal level. (II) A succeeding contractional stage involved the reactivation of the inherited Triassic-Jurassic suture and the tectonic erosion of a frontal compartment of the continental margin. After an incipient underplating, slivers of this continental compartment returned within a time span of about 20 Ma. (III) A final Late Cretaceous subduction stage evolved under the conditions of an oblique SW-NE oriented plate convergence and is characterized by extensional pulses, as may be concluded from the structural setting of the giant Antioquia batholith. In the Campanian subduction definitely locked, as evidenced by the regional buckling of the forearc realm and a rebound of the upper continental plate. Both onset and shutoff of this subduction cycle may be linked to deformation phases and are dated by syntectonic, fault-guided intrusions. This scenario of a forearc origin of the basic igneous province calls for the existence of two paired subduction zones: on its outer margin the subducting Farallon slab imposed a trench-parallel mantle flow and constrained an expansion of the forarc basin by slab rollback. On its inner margin, a secondary subduction compensated a surplus expansion of the actively forming forearc basin.</p>

scholarly journals Improved finite-source inversion through joint measurements of rotational and translational ground motions: A theoretical study

2016 ◽  
Author(s):  
Michael Reinwald ◽  
Moritz Bernauer ◽  
Heiner Igel ◽  
Stefanie Donner
Keyword(s):  
Inverse Problem ◽  
Ground Motions ◽  
Source Parameters ◽  
Normal Fault ◽  
Seismic Source ◽  
Vertical Gradient ◽  
Vertical Displacement ◽  
Source Inversion ◽  
Additional Information ◽  
Finite Source

Abstract. With the prospects of seismic equipment being able to measure rotational ground motions in a wide frequency and amplitude range in the near future we engage in the question how this type of ground motion observation can be used to solve the seismic inverse problem. In this paper, we focus on the question, whether finite source inversion can benefit from additional observations of rotational motion. Keeping the overall number of traces constant, we compare observations from a surface seismic network with 44 3-component translational sensors (classic seismometers) with those obtained with 22 6-component sensors (with additional 3-component rotational motions). Synthetic seismograms are calculated for known finite-source properties. The corresponding inverse problem is posed in a probabilistic way using the Shannon information content as measure how the observations constrain the seismic source properties. We minimize the influence of the source receiver geometry around the fault by statistically analyzing six-component (three velocity and three rotation rate) inversions with a random distribution of receivers. The results show that with the 6-C subnetworks the source properties are not only equally well recovered (even that would be benefitial because of the substantially reduced logistics installing half the sensors) but statistically some source properties are almost always better resolved. We assume that this can be attributed to the fact that the (in particular vertical) gradient information is contained in the additional motion components. We compare these effects for strike-slip and normal-faulting type sources and confirm that the increase in inversion quality for kinematic source parameters is even higher for the normal fault. This indicates that the inversion benefits from the additional information provided by the horizontal rotation rates, i.e. information about the vertical displacement gradient.

scholarly journals CO-SEISMIC GRAVITY GRADIENT CHANGES OF THE 2006–2007 GREAT EARTHQUAKES IN THE CENTRAL KURIL ISLANDS FROM GRACE OBSERVATIONS

2017 ◽  
Vol XLII-4/W4 ◽  
pp. 517-522
Author(s):  
A. Rahimi ◽  
M. Shahrisvand
Keyword(s):  
Normal Fault ◽  
Gravity Anomalies ◽  
Kuril Islands ◽  
Gravity Gradient ◽  
Gravitational Gradient ◽  
North East ◽  
Earth Gravity ◽  
Central Kuril Islands ◽  
Frequency Components ◽  
Grace Satellites

GRACE satellites (the Gravity Recovery And climate Experiment) are very useful sensors to extract gravity anomalies after earthquakes. In this study, we reveal co-seismic signals of the two combined earthquakes, the 2006 Mw8.3 thrust and 2007 Mw8.1 normal fault earthquakes of the central Kuril Islands from GRACE observations. We compute monthly full gravitational gradient tensor in the local north-east-down frame for Kuril Islands earthquakes without spatial averaging and de-striping filters. Some of gravitational gradient components (e.g. ΔVxx, ΔVxz) enhance high frequency components of the earth gravity field and reveal more details in spatial and temporal domain. Therefore, co-seismic activity can be better illustrated. For the first time, we show that the positive-negative-positive co-seismic ΔVxx due to the Kuril Islands earthquakes ranges from − 0.13 to + 0.11 milli Eötvös, and ΔVxz shows a positive-negative-positive pattern ranges from − 0.16 to + 0.13 milli Eötvös, agree well with seismic model predictions.

scholarly journals Geometry of the inverted Cretaceous Chañarcillo Basin based on 2-D gravity and field data. An approach to the structure of the western Central Andes of northern Chile

2015 ◽  
Vol 7 (3) ◽  
pp. 2311-2346
Author(s):  
F. Martínez ◽  
A. Maksymowicz ◽  
H. Ochoa ◽  
D. Díaz
Keyword(s):  
Normal Fault ◽  
Gravity Anomalies ◽  
Integrated Approach ◽  
Central Andes ◽  
Fault System ◽  
Northern Chile ◽  
Gravity Gradients ◽  
Structural Geometry ◽  
Geological Information ◽  
New Ideas

Abstract. This paper discusses an integrated approach that provides new ideas about the structural geometry of the NNE-striking, Cretaceous Chañarcillo Basin located along the eastern Coastal Cordillera in the western Central Andes of northern Chile (27–28° S). The results obtained from the integration of two transverse (E–W) gravity profiles with previous geological information, show that the architecture of this basin is defined by a large NNE–SSE-trending and east-vergent anticline ("Tierra Amarilla Anticlinorium"), which is related to the positive reactivation of a former Cretaceous normal fault (Elisa de Bordos Master Fault). Moreover, intercalations of high and low gravity anomalies and steep gravity gradients reveal a set of buried, west-tilted half-grabens associated with a synthetic normal fault pattern. These results, together with the uplift and folding style of the Cretaceous syn-rift recognized within the basin, suggest that their complete structural geometry could be explained by an inverted fault system linked to the shortening of pre-existing Cretaceous normal fault systems. Ages of the synorogenic deposits exposed unconformably over the frontal limb of the Tierra Amarilla Anticlinorium confirm a Late Cretaceous age for the Andean deformation and tectonic inversion of the basin.

scholarly journals SOURCE PARAMETERS of STRONG EARTHQUAKES OCCURRED in the BAIKAL REGION and TRANSBAIKALIA in 2015

2021 ◽  
pp. 217-225
Author(s):  
A. Filippova ◽  
N. Gileva
Keyword(s):  
Baikal Region ◽  
Source Parameters ◽  
Seismic Hazard Assessment ◽  
Normal Fault ◽  
Baikal Rift Zone ◽  
Body Waves ◽  
Small Scale ◽  
Seismic Events ◽  
Study Region ◽  
Moment Tensors

We calculated seismic moment tensors in a double-couple approximation (focal mechanisms, scalar seismic moments, and moment magnitudes) and hypocentral depths for twenty earthquakes with Mw≥4.2 that occurred in the Baikal region and Transbaikalia in 2015. The initial data were amplitude spectra of Rayleigh and Love waves obtained from their records at the broadband seismic stations of the IRIS and the DK networks and first-motion polarities of body waves recorded at regional distances. A combination of the normal fault and strike-slip movements dominate in the sources of the major part of the study earthquakes. For the strongest of the considered seismic events (Mw≥4.6), the subvertical compression and subhorizontal tension in the SE-NW direction prevail, i.e. the tension is perpendicular to the main structures of the Baikal rift zone. The seismic events with Mw<4.6 are characterized by a more scattered orientation of compression and tension axis that could be caused, for instance, by stress redistribution in small-scale crustal blocks after stronger earthquakes. The obtained results are of great value for issues concerned with seismic hazard assessment and the development of geodynamical models of the lithosphere evolution of the study region.

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