Characteristics and impact of environmental shaking in the Taipei metropolitan area

Examining continuous seismic data recorded by a dense broadband seismic network throughout Taipei shows for the first time, the nature of seismic noise in this highly populated metropolitan area. Using 140 broadband stations in a 50 km × 69 km area, three different recurring, strong noise signals characterized by dominant frequencies of 2–20 Hz, 0.25–1 Hz, and < 0.2 Hz are explored. At frequencies of 2–20 Hz, the seismic noise exhibits daily and weekly variations, and a quiescence during the Chinese New Year holidays. The largest amplitude occurred at a station located only 400 m from a traffic-roundabout, one of the busiest intersections in Taipei, suggesting a possible correlation between large amplitude and traffic flow. The median daily amplitude for the < 0.2 Hz and 0.2–1.0 Hz frequency bands is mostly synchronized with high similarity between stations, indicating that the sources are persistent oceanic or atmospheric perturbations across a large area. The daily amplitude for the > 2 Hz band, however, is low, indicating a local source that changes on shorter length scales. Human activities responsible for the 2–40 Hz energy in the city, we discovered, are able to produce amplitudes approximately 2 to 1500 times larger than natural sources. Using the building array deployed in TAIPEI 101, the tallest building in Taiwan, we found the small but repetitive ground vibration induced by traffic has considerable effect on the vibration behavior of the high-rise building. This finding urges further investigation not only on the dynamic and continuous interaction between vehicles, roads, and buildings, but also the role of soft sediment on such interaction.

Coastal imbalance: generation of oceanic Kelvin waves by atmospheric perturbations

The response of a semi-infinite ocean to a slowly travelling atmospheric perturbation crossing the coast provides a simple example of the breakdown of nearly geostrophic balance induced by a boundary. We examine this response in the linear shallow-water model at small Rossby number $\varepsilon \ll 1$ . Using matched asymptotics, we show that a long Kelvin wave, with $O(\varepsilon ^{-1})$ length scale and $O(\varepsilon )$ amplitude relative to quasi-geostrophic response, is generated as the perturbation crosses the coast. Accounting for this Kelvin wave restores the conservation of mass that is violated in the quasi-geostrophic approximation.

Whispering of the city: Characteristics and origin of environmental shaking in the Taipei metropolitan area

Examining continuous seismic data recorded by a dense broadband seismic network throughout Taipei shows for the first time, the nature of seismic noise in this highly populated metropolitan. Using 140 broadband stations in a 50 km x 69 km area, three different recurring, strong noise signals characterized by dominant frequencies of 2–20 Hz, 0.25-1 Hz, and < 0.2 Hz are explored. At frequencies of 2–20 Hz, the seismic noise exhibits daily and weekly variations, and a quiescence during the Chinese New Year holidays. The largest amplitude occurred at a station located only 400 m from a traffic-roundabout, one of the busiest intersections in Taipei, suggesting a possible correlation between large amplitude with traffic flow. The median daily amplitude for the < 0.2 Hz and 0.2-1.0 Hz frequency bands are mostly synchronized with high similarity between stations, indicating that the sources are persistent oceanic or atmospheric perturbations across a large area. The daily amplitude for the > 2 Hz band, however, is low, indicating a local source that changes on shorter length scales. Human activities responsible for the 2–40 Hz energy in the city, we discovered, are able to produce amplitudes approximately 2 to 1500 times larger than natural sources.

UNDERSTANDING VERTICAL GROUND DISPLACEMENT FROM P-SBAS USING GETIS-ORD GI* STATISTIC

The Differential Synthetic Aperture Radar Interferometric (DInSAR) algorithm has already shown its importance in volcanicmonitoring. However, it is limited by atmospheric perturbations or temporal decorrelation, implying the existence of lowcoherencerecords that must be discarded. In vast studied areas, with thousands of points unevenly distributed, theinterpretation of the results is usually complicated. This text presents an analysis of the vertical component variation onTenerife island (Canary Islands), from 2005 to 2010, using Getis-Ord Gi* spatial statistic on ENVISAT DinSAR images.The ascending and descending images have been processed using the Parallel Small BAseline Subset (P-SBAS)algorithm, within ESA Grid Processing on Demand cloud environment. From Line of Sight results of both tracks, the verticaldeformation speeds have been calculated over 72,207 points with high coherence (&gt; 0.7). Finally, the Gi* statistic hasbeen applied, obtaining a map with statistical significance, where the high values of Gi*, both positive and negative, implythe spatial clustering of likely ground movements. This map highlights areas with variable vertical kinematics on TenerifeIsland, contributing to understanding of its geodynamics. The displacements obtained coincide with previous studies, evenshowing possible new relationships between some phenomena that should be considered. The Gi* spatial statistic is anefficient and quick tool to extract information in a regional scale kinematic study.

Modeling the evolution of pulse-like perturbations in atmospheric carbon and carbon isotopes: the role of weathering–sedimentation imbalances

Measurements of carbon isotope variations in climate archives and isotope-enabled climate modeling advance the understanding of the carbon cycle. Perturbations in atmospheric CO2 and in its isotopic ratios (δ13C, Δ14C) are removed by different processes acting on different timescales. We investigate these differences on timescales of up to 100 000 years in pulse-release experiments with the Bern3D-LPX Earth system model of intermediate complexity and by analytical solutions from a box model. On timescales from years to many centuries, the atmospheric perturbations in CO2 and δ13CO2 are reduced by air–sea gas exchange, physical transport from the surface to the deep ocean, and by the land biosphere. Isotopic perturbations are initially removed much faster from the atmosphere than perturbations in CO2 as explained by aquatic carbonate chemistry. On multimillennial timescales, the CO2 perturbation is removed by carbonate compensation and silicate rock weathering. In contrast, the δ13C perturbation is removed by the relentless flux of organic and calcium carbonate particles buried in sediments. The associated removal rate is significantly modified by spatial δ13C gradients within the ocean, influencing the isotopic perturbation of the burial flux. Space-time variations in ocean δ13C perturbations are captured by principal components and empirical orthogonal functions. Analytical impulse response functions for atmospheric CO2 and δ13CO2 are provided. Results suggest that changes in terrestrial carbon storage were not the sole cause for the abrupt, centennial-scale CO2 and δ13CO2 variations recorded in ice during Heinrich stadials HS1 and HS4, though model and data uncertainties prevent a firm conclusion. The δ13C offset between the Penultimate Glacial Maximum and Last Glacial Maximum reconstructed for the ocean and atmosphere is most likely caused by imbalances between weathering, volcanism, and burial fluxes. Our study highlights the importance of isotopic fluxes connected to weathering–sedimentation imbalances, which so far have been often neglected on glacial–interglacial timescales.