The seismic velocity structure of northern Appalachian crust around western Newfoundland

1992 ◽  
Vol 29 (3) ◽  
pp. 462-478 ◽  
Author(s):  
H. Karin Michel ◽  
K. E. Louden ◽  
F. Marillier ◽  
I. Reid
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Seismic Velocity Structure ◽  
The North ◽  
Crustal Block ◽  
Crustal Velocity ◽  
Crustal Velocity Structure ◽  
Sediment Layers ◽  
Lower Crustal ◽  
Broad Region

The crustal velocity structure beneath western Newfoundland is constrained by a reanalysis of older, regional refraction profiles together with an analysis of one new profile. Initial interpretation of the older data gave inconsistent and discontinuous structures that are difficult to reconcile with more recent deep reflection profiles. We also show that traveltimes predicted by the earlier models often do not yield acceptable fits to the original observations. Our reinterpretation reveals a simpler pattern, in which the crust is characterized by a persistent, high-velocity, lower crustal (HVLC) layer. This layer has velocities of 7.0–7.9 kmls and thicknesses of 5–23 km. It is thickest beneath the Grenville crustal block, east of the Appalachian structural front, and thins or is possibly absent within the Central block. Analysis of the new, much higher resolution profile off western Newfoundland confirms the existence of the HVLC layer with a velocity of 7.2 kmls and thicknesses of 11–19 km, increasing to the northeast. The upper crust has well-defined velocities of 6.2–6.4 kmls and is overlain by a complex sandwich of sediment layers with principal velocities of 3.9, 4.95, and 5.58 kmls and maximum total thicknesses of 8.5 km in the south to 5.5 km in the north. Total crustal thickness varies from 39 to 43 km from south to north. Comparison of the velocity–depth models with the pattern of deep crustal reflectivity revealed by deep multichannel profiles shows that the HVLC layer is coincident with a zone of flat-lying reflectors that terminate to the west at the base of the crust beneath the Appalachian structural front. The HVLC may continue eastward to cover a broad region of central Newfoundland as suggested by the older data, but its association with the reflectivity is not clear.

scholarly journals Supplemental Material: Seismic velocity structure of the Queen Charlotte terrace off western Canada in the region of the 2012 Haida Gwaii Mw 7.8 thrust earthquake

2020 ◽  
Author(s):  
Michael Riedel ◽  
et al.
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Head Wave ◽  
Western Canada ◽  
Haida Gwaii ◽  
Seismic Velocity Structure ◽  
Crustal Velocity ◽  
Sediment Layers ◽  
Velocity Layer ◽  
Ray Paths

Modeled ray paths and comparisons to picked arrivals are shown here for the refractions in sediment layers 1 (Fig. S1) and 2 (Fig.S2), the reflections from the bottoms of sediment layers 1 (Fig. S3) and 2 (Fig. S4), the refraction from the bottom of the crustal velocity layer (Fig. S5), and the head-wave from the bottom of the crustal-velocity layer (Fig. S6).

scholarly journals Supplemental Material: Seismic velocity structure of the Queen Charlotte terrace off western Canada in the region of the 2012 Haida Gwaii Mw 7.8 thrust earthquake

2020 ◽  
Author(s):  
Michael Riedel ◽  
et al.
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Head Wave ◽  
Western Canada ◽  
Haida Gwaii ◽  
Seismic Velocity Structure ◽  
Crustal Velocity ◽  
Sediment Layers ◽  
Velocity Layer ◽  
Ray Paths

Modeled ray paths and comparisons to picked arrivals are shown here for the refractions in sediment layers 1 (Fig. S1) and 2 (Fig.S2), the reflections from the bottoms of sediment layers 1 (Fig. S3) and 2 (Fig. S4), the refraction from the bottom of the crustal velocity layer (Fig. S5), and the head-wave from the bottom of the crustal-velocity layer (Fig. S6).

scholarly journals Supplemental Material: Seismic velocity structure of the Queen Charlotte terrace off western Canada in the region of the 2012 Haida Gwaii Mw 7.8 thrust earthquake

2020 ◽  
Author(s):  
Michael Riedel ◽  
et al.
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Head Wave ◽  
Western Canada ◽  
Haida Gwaii ◽  
Seismic Velocity Structure ◽  
Crustal Velocity ◽  
Sediment Layers ◽  
Velocity Layer ◽  
Ray Paths

Modeled ray paths and comparisons to picked arrivals are shown here for the refractions in sediment layers 1 (Fig. S1) and 2 (Fig.S2), the reflections from the bottoms of sediment layers 1 (Fig. S3) and 2 (Fig. S4), the refraction from the bottom of the crustal velocity layer (Fig. S5), and the head-wave from the bottom of the crustal-velocity layer (Fig. S6).

Crustal velocity structure from SAREX, the Southern Alberta Refraction Experiment

2002 ◽  
Vol 39 (3) ◽  
pp. 351-373 ◽  
Author(s):  
Ron M Clowes ◽  
Michael JA Burianyk ◽  
Andrew R Gorman ◽  
Ernest R Kanasewich
Keyword(s):  
Velocity Structure ◽  
Data Interpretation ◽  
Crustal Thickening ◽  
Tectonic Zone ◽  
Crustal Layer ◽  
Crustal Velocity ◽  
Crustal Velocity Structure ◽  
Southern Alberta ◽  
Magmatic Underplating ◽  
Lower Crustal

Lithoprobe's Southern Alberta Refraction Experiment, SAREX, extends 800 km from east-central Alberta to central Montana. It was designed to investigate crustal velocity structure of the Archean domains underlying the Western Canada Sedimentary Basin. From north to south, SAREX crosses the Loverna domain of the Hearne Province, the Vulcan structure, the Medicine Hat block (previously considered part of the Hearne Province), the Great Falls tectonic zone, and the northern Wyoming Province. Ten shot points along the profile in Canada were recorded on 521 seismographs deployed at 1 km intervals. To extend the line, an additional 140 seismographs were deployed at intervals of 1.25–2.50 km in Montana. Data interpretation used an iterative application of damped least-squares inversion of traveltime picks and forward modeling. Results show different velocity structures for the major blocks (Loverna, Medicine Hat, and Wyoming), indicating that each is distinct. Wavy undulations in the velocity structure of the Loverna block may be associated with internal crustal deformation. The most prominent feature of the model is a thick (10–25 km) lower crustal layer with high velocities (7.5–7.9 km/s) underlying the Medicine Hat and Wyoming blocks. Based on data from lower crustal xenoliths in the region, this layer is interpreted to be the result of Paleoproterozoic magmatic underplating. Crustal thickness varies from 40 km in the north to almost 60 km in the south, where the high-velocity layer is thickest. Uppermost mantle velocities range from 8.05 to 8.2 km/s, with the higher values below the thicker crust. Results from SAREX and other recent studies are synthesized to develop a schematic representation of Archean to Paleoproterozoic tectonic development for the region encompassing the profile. Tectonic processes associated with this development include collisions of continental blocks, subduction, crustal thickening, and magmatic underplating.

Seismic velocity structure along the North Anatolian Fault beneath the Central Marmara Sea and its implication for seismogenesis

2021 ◽  
Author(s):  
Yojiro Yamamoto ◽  
Dogan Kalafat ◽  
Ali Pinar ◽  
Narumi Takahashi ◽  
Remzi Polat ◽  
...  
Keyword(s):  
High Velocity ◽  
Seismic Activity ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Large Earthquake ◽  
Marmara Sea ◽  
Ocean Bottom ◽  
Seismic Velocity Structure ◽  
The North ◽  
Depth Direction

Summary The offshore part of the North Anatolian Fault (NAF) beneath the Marmara Sea is a well-known seismic gap for future M > 7 earthquakes in the sense that more than 250 years have passed since the last major earthquake in the Central Marmara region. Although many studies discussed the seismic potential for the future large earthquake in this region on the basis of historical record, geodetic, and geological observations, it is difficult to evaluate the actual situation on the seismic activity and structure along the NAF beneath the Marmara Sea due to the lack of ocean bottom seismic observations. Using ocean bottom seismometer observations, an assessment of the location of possible asperities that could host an expected large earthquake is undertaken based on heterogeneities in the microseismicity distribution and seismic velocity structure. Specifically, seismic tomography and precise hypocenter estimations are conducted using offshore seismic data whose recording period is 11 months. About five times more microearthquakes are detected with respect to events recorded in a land-based catalog. A comparison with previously published results from offshore observation data suggests that the seismicity pattern had not changed from September 2014 to May 2017. The location accuracy of microearthquakes is greatly improved from only the land-based earthquake catalog, particularly for depth direction. There are several aseismic and inactive zones of microearthquake, and the largest one is detected using land-based seismic observation, whereas other zones are newly detected via offshore observations. The obtained velocity model shows a strong lateral contrast, with two changing points. The western changing point corresponds to a segmentation boundary, where the dip angle of the NAF segments changed. High-velocity zones from tomographic images are characterized by low seismicity eastward of the segment boundary. To the east of 28.50° E, the high-velocity zone becomes thicker in the depth direction and is characterized by low seismicity. Although the low seismic activity alone could be interpreted as both strong coupling and fully creeping, the high-velocity features at the same can be concluded that these zones are consist of brittle material and strong coupling. From comparison with other geodetic and seismic studies, we interpret these zones as locked zones that had been ruptured by the past large earthquakes and could be ruptured by future ones. These zones might accumulate strain since the mainshock rupture associated with the May 1766 Ms7.3 earthquake, the latest major earthquake in this region.

Seismic velocity structure of the upper inner core in the north polar region

2020 ◽  
pp. 106636
Author(s):  
Toshiki Ohtaki ◽  
Satoru Tanaka ◽  
Satoshi Kaneshima ◽  
Weerachai Siripunvaraporn ◽  
Songkhun Boonchaisuk ◽  
...  
Keyword(s):  
Polar Region ◽  
Inner Core ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Seismic Velocity Structure ◽  
The North ◽  
North Polar
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