Multi-method site characterization to verify the hard rock (Site Class A) assumption at 25 seismograph stations across Eastern Canada

Site characterization is a crucial component in assessing seismic hazard, typically involving in situ shear-wave velocity ( VS) depth profiling, and measurement of site amplification including site period. Noninvasive methods are ideal for soil sites and become challenging in terms of field logistics and interpretation in more complex geologic settings including rock sites. Multiple noninvasive active- and passive-seismic techniques are applied at 25 seismograph stations across Eastern Canada. It is typically assumed that these stations are installed on hard rock. We investigate which site characterization methods are suitable at rock sites as well as confirm the hard rock assumption by providing VS profiles. Active-source compression-wave refraction and surface wave array techniques consistently provide velocity measurements at rock sites; passive-source array testing is less consistent but it is our most suitable method in constraining the rock VS. Bayesian inversion of Rayleigh wave dispersion curves provides quantitative uncertainty in the rock VS. We succeed in estimating rock VS at 16 stations, with constrained rock VS estimates at 7 stations that are consistent with previous estimates for Precambrian and Paleozoic rock types. The National Building Code of Canada uses solely the time-averaged shear-wave velocity of the upper 30 m ( VS30) to classify rock sites. We determine a mean VS30 of ∼ 1600 m/s for 16 Eastern Canada stations; the hard rock assumption is correct (>1500 m/s) but not as hard as often assumed (∼2000 m/s). Mean variability in VS30 is ∼400 m/s and can lead to softer rock classifications, in particular, for Paleozoic rock types with lower average rock VS near the hard/soft rock boundary. Microtremor and earthquake horizontal-to-vertical spectral ratios are obtained and provide site period classifications as an alternative to VS30.

Exceptionally preserved Milankovitch cycles in Lower Devonian argillaceous limestone of the Hudson Valley, New York State (USA)

<p>Uncertainties on the radiometric ages of Devonian stage boundaries are currently on the order of several millions of years. A cyclostratigraphic approach is the foremost way forward to improve the Devonian geological time scale. To do so requires well-preserved continuous records, as well as reliable paleoclimatic proxies.  The NY Route 199 section, from Kingston, in the Hudson Valley of eastern New York, is a road cut outcrop, which exposes most of the Schoharie Formation. It corresponds to the upper portion of the Emsian Stage (upper Lower Devonian, ~400 to ~394 Ma), with essentially continuous deposition. The lithology consists of a mixed siliciclastic-carbonate succession with overall increasing carbonate upsection, showing various degrees of bioturbation (traces includes primarily Zoophycos, Planolites and Chondrites); colors range from white to beige, brown or dark grey. The quality of most of the outcrop is so remarkable that the color variations by themselves permit recognition of Milankovitch cycles, with prominent bundles of light and dark beds. One type of cycle expression is represented by a succession of about six darker beds nested between lighter beds, which is interpreted as six precession cycles within a short eccentricity cycle (precession in the Devonian was ~17 kyr).</p><p>Samples were collected every 2 cm through 38 m of the section for magnetic susceptibility measurements. On top of these measurements, we provide elemental geochemistry, carbon isotopes and hysteresis measurements (every 50 cm) to constrain the depositional setting and the diagenesis. Hysteresis measurements show that despite being remagnetized (throughout the Appalachians, these Paleozoic rock sequences are all remagnetized during the Variscan-Alleghenian Orogeny), the magnetic susceptibility reflects depositional information. The geochemistry and carbon isotopes give insight into the occurrence of oxic/reducing conditions and detrital inputs. Milankovitch cycles are visible on the outcrop and in the magnetic susceptibility record, allowing a precise floating timescale framework to be constructed for this interval.</p>

Late Paleozoic rock deformation of the Kurai block: structural‐kinematic analysis (upper Kuraika river, Gorny Altai, Russia)

In the Kurai ridge located in the southeastern Gorny Altai (Altai Mountains, Russia) metamorphic rocks of the Kurai complex are widely developed: granite‐gneisses, crystalline schists and amphibolites, including widespread Early Carboniferous mylonites and blastomylonites. Oriented samples of blastomylonites were taken from the upper reaches of the Kuraika river for the microstructural study aimed to determine the kinematics of movements. The analyses of thin cut samples show structural‐kinematic indicators that suggest two deformation events (left‐lateral shearing, then right‐lateral shearing).

Detrital monazite from Upper Jurassic sediments in the central part of the Frolov megadepression, Western Siberia: chemical dating and provenances

Detrital monazite from Upper Jurassic sediments in the central part of the Frolov megadepression, West Siberian megabasin, is studied. Chemical composition of the mineral is studied and data on its age (chemical dating) are presented. Most monazite clasts are characterized by low roundness and their age corresponds to the Lower Paleozoic. Upper Jurassic sediments were likely derived not only from the local Early Paleozoic rock complexes (altaides), which make up the pre-Jurassic basement of the Frolov megadepression, but also from rocks located east and south of this megadepression.

THE IMPORTANCE OF GEOLOGICAL HERITAGE RESOURCES IN LAND USE PLANNING: EXPERIENCE FROM LANGKAWI GEOPARK

Being an oldest landmass with the most complete Paleozoic rock sequence Langkawi archipelago hosts the richest geological diversity and heritage resources in the country. As a popular tourist destination, the scenic beauty has attracted tourists to Langkawi without them realising that the beauty has been created by the islands’ rich geological heritage diversity. To date more than 90 geoheritage sites of highly significant scientific, aesthetic, social or recreational value have been identified. Some of these geoheritage sites have become popular tourist sites. To ensure the sustainability of the tourism industry Langkawi needs to have a comprehensive and practical conservation strategy and mechanism. Without a good conservation policy the geoheritage sites are constantly under threat and under stress due to the need of space for development. To ensure the sustainability of these natural resources it is timely to include geoheritage sites in future land use planning.

THE IMPORTANCE OF GEOLOGICAL HERITAGE RESOURCES IN LAND USE PLANNING: EXPERIENCE FROM LANGKAWI GEOPARK

Being an oldest landmass with the most complete Paleozoic rock sequence Langkawi archipelago hosts the richest geological diversity and heritage resources in the country. As a popular tourist destination, the scenic beauty has attracted tourists to Langkawi without them realising that the beauty has been created by the islands’ rich geological heritage diversity. To date more than 90 geoheritage sites of highly significant scientific, aesthetic, social or recreational value have been identified. Some of these geoheritage sites have become popular tourist sites. To ensure the sustainability of the tourism industry Langkawi needs to have a comprehensive and practical conservation strategy and mechanism. Without a good conservation policy the geoheritage sites are constantly under threat and under stress due to the need of space for development. To ensure the sustainability of these natural resources it is timely to include geoheritage sites in future land use planning.

Murchison's Research Method: An Example from Southern Norway

Roderick Impey Murchison (1792-1871) was an eminent geologist whose reputation was in large part based on a research method that comprised an efficient fieldwork procedure followed by public presentations and publication of his findings. His research method enabled him to survey large areas rapidly, apply recent advances in the science of geology to those large areas, and present his results in a timely and widespread manner with maximum impact. This paper focuses on Murchison's two-week visit to Norway in 1844, and the presentation of his findings in the aftermath of that visit, to illustrate his research method in action. Not only did his work result in a significant advance in the understanding of the geology of Norway, but Murchison also applied his Norway results to issues of wide interest in the developing science of geology. In particular, his work in Norway resulted in: (1) an appreciation of the extent of Paleozoic rock systems in Norway; (2) a new name, Azoic, for the older, nonfossiliferous basement rocks; (3) the recognition of the effects of younger igneous intrusions on country rock; (4) a proposed classification scheme for metamorphic grade; and (5) a proposed classification scheme for igneous rocks based on the timing of intrusion.

A Reconnaissance Geophysical Survey of the Kawartha Lakes and Lake Simcoe, Ontario

ABSTRACT A marine geophysical survey program has been conducted in lakes of southern Ontario. The survey was designed to detect neotectonic features, if they exist, and to evaluate their geological importance. High-resolution single- and multichannel seismic reflection profiling were used to delineate late- and post-glacial sedimentary strata and structures, as well as the sediment/bedrock interface, in the Kawartha Lakes and Lake Simcoe. Results show that two seismostratigraphic sequences are common within the unconsolidated overburden. The lower unit exhibits a parallel reflection configuration having strong reflection amplitudes, whereas the upper unit is acoustically transparent and overlies the lower unit conformably in some places and unconformably in others. Both units vary in thickness within lakes and from lake to lake. Typical subbottom profiles of Precambrian rock surfaces are rolling; those of Paleozoic rock surfaces are smooth. At one location in Lower Buckhorn Lake, tilted rock surfaces may be faulted but disturbance of overlying glacioge-nic sediments was not observed. In western Lake Simcoe and Kempenfelt Bay, slumping into graben-like features was observed. Also in Lake Simcoe, a diapiric feature was documented. It is speculated that these disturbances most likely result from glacier ice block melting and fluid migration. A tectonic origin, however, cannot be discounted at this stage of investigation. Additional systematic marine geophysical surveys are required in the future to map features in detail to determine whether they are of neotectonic or glaciotectonic origin.