Geology topics

Natalia Ruppert

Publications and source records attributed to Natalia Ruppert.

5 recordsLinked to original sources

USGS2021

Response of an asymmetrical five-story building in Fairbanks, Alaska during the November 30, 2018 M7.1 Anchorage, Alaska earthquake

A recently constructed, five-story, asymmetrical steel building on the campus of the University of Alaska, Fairbanks was equipped with a strong-motion array that recorded the M7.1 Anchorage earthquake of November 30, 2018 at an epicentral distance of 408 km. The largest recorded peak accelerations at the basement and top of the building are 0.021g and 0.071g, respectively. The steel building is designed with several bays that utilize K-shaped buckling restrained braces. The building response records allow identification of fundamental periods (frequencies) as 0.73s (1.4 Hz), 0.63s (1.60 Hz), and 0.56s (1.78 Hz) in the NS, EW, and torsional directions, respectively. System identification computations resulted in estimated critical damping percentages as 7.7% and 4.7 % in the NS and EW directions, respectively. At this low-level of shaking, the building is not expected to (and did not) experience observable damage, which is confirmed with very small average drift ratios. This is the first time a seismic response from this structural array has been analyzed.

Alaska↗

USGS2019

Preface to the focus section on the 30 November 2018 Mw 7.1 Anchorage, Alaska earthquake

On 30 November 2018, a magnitude ( ⁠ M w "> M w ⁠ ) 7.1 intraslab earthquake occurred under the most densely populated area of Alaska, ∼ 12    km "> ∼ 12 km north of downtown Anchorage. It generated the strongest ground shaking in the greater Anchorage area since the 1964 M w "> M w 9.2 Great Alaska earthquake. Although the 30 November 2018 earthquake did not cause deaths or serious injuries, its economical and psychological impacts on the local population were profound. It caused widespread power outages, structural and nonstructural damage to public and private buildings, and damage to roadways and railways, and resulted in closures of several schools and multiple businesses.

Alaska↗

USGS2019

The 30 November 2018 Mw7.1 Anchorage Earthquake

The M w "> M w 7.1 47 km deep earthquake that occurred on 30 November 2018 had deep societal impacts across southcentral Alaska and exhibited phenomena of broad scientific interest. We document observations that point to future directions of research and hazard mitigation. The rupture mechanism, aftershocks, and deformation of the mainshock are consistent with extension inside the Pacific plate near the down‐dip limit of flat‐slab subduction. Peak ground motions > 25 % g "> g >25%g were observed across more than 8000    km 2 "> 8000 km 2 ⁠ , though the most violent near‐fault shaking was avoided because the hypocenter was nearly 50 km below the surface. The ground motions show substantial variation, highlighting the influence of regional geology and near‐surface soil conditions. Aftershock activity was vigorous with roughly 300 felt events in the first six months, including two dozen aftershocks exceeding M 4.5. Broad subsidence of up to 5 cm across the region is consistent with the rupture mechanism. The passage of seismic waves and possibly the coseismic subsidence mobilized ground waters, resulting in temporary increases in stream flow. Although there were many failures of natural slopes and soils, the shaking was insufficient to reactivate many of the failures observed during the 1964 M 9.2 earthquake. This is explained by the much shorter duration of shaking as well as the lower amplitude long‐period motions in 2018. The majority of observed soil failures were in anthropogenically placed fill soils. Structural damage is attributed to both the failure of these emplaced soils as well as to the ground motion, which shows some spatial correlation to damage. However, the paucity of instrumental ground‐motion recordings outside of downtown Anchorage makes these comparisons challenging. The earthquake demonstrated the challenge of issuing tsunami warnings in complex coastal geographies and highlights the need for a targeted tsunami hazard evaluation of the region. The event also demonstrates the challenge of estimating the probabilistic hazard posed by intraslab earthquakes.

Alaska↗

USGS2017

The Peters Hills basin, a Neogene wedge-top basin on the Broad Pass thrust fault, south-central Alaska

The Neogene Peters Hills basin is a small terrestrial basin that formed along the south flank of the Alaska Range during a time in which there was regional shortening. The formation of the Peters Hills basin is consistent with it being a wedge-top basin that formed on top of the active southeast-vergent Broad Pass thrust fault. Movement along this thrust raised a ridge of Jurassic and Cretaceous metasedimentary rocks, which then trapped behind it Miocene and Pliocene sediments that were derived from the growing Alaska Range. The presence of this thrust fault is consistent with regional structural, stratigraphic, seismicity, gravity, and aeromagnetic data. The Peters Hills basin is no longer a depocenter, but if the Broad Pass thrust remains active, it would help explain the westward decrease in Quaternary slip rate along the Denali fault system, and it may constitute a seismic hazard that could produce earthquakes in the M w 7.6–7.8 range.

Alaska↗

USGS2012

Afterslip, tremor, and the Denali fault earthquake

We tested the hypothesis that afterslip should be accompanied by tremor using observations of seismic and aseismic deformation surrounding the 2002 M 7.9 Denali fault, Alaska, earthquake (DFE). Afterslip happens more frequently than spontaneous slow slip and has been observed in a wider range of tectonic environments, and thus the existence or absence of tremor accompanying afterslip may provide new clues about tremor generation. We also searched for precursory tremor, as a proxy for posited accelerating slip leading to rupture. Our search yielded no tremor during the five days prior to the DFE or in several intervals in the three months after. This negative result and an array of other observations all may be explained by rupture penetrating below the presumed locked zone into the frictional transition zone. While not unique, such an explanation corroborates previous models of megathrust and transform earthquake ruptures that extend well into the transition zone.

Alaska↗