Geology topics

E. Karaca

Publications and source records attributed to E. Karaca.

3 recordsLinked to original sources

USGS2009

Decision making with epistemic uncertainty under safety constraints: An application to seismic design

The problem of accounting for epistemic uncertainty in risk management decisions is conceptually straightforward, but is riddled with practical difficulties. Simple approximations are often used whereby future variations in epistemic uncertainty are ignored or worst-case scenarios are postulated. These strategies tend to produce sub-optimal decisions. We develop a general framework based on Bayesian decision theory and exemplify it for the case of seismic design of buildings. When temporal fluctuations of the epistemic uncertainties and regulatory safety constraints are included, the optimal level of seismic protection exceeds the normative level at the time of construction. Optimal Bayesian decisions do not depend on the aleatory or epistemic nature of the uncertainties, but only on the total (epistemic plus aleatory) uncertainty and how that total uncertainty varies randomly during the lifetime of the project. ?? 2009 Elsevier Ltd. All rights reserved.

Probabilistic Engineering Mechanics↗

USGS2008

Development of hazard-compatible building fragility and vulnerability models

We present a methodology for transforming the structural and non-structural fragility functions in HAZUS into a format that is compatible with conventional seismic hazard analysis information. The methodology makes use of the building capacity (or pushover) curves and related building parameters provided in HAZUS. Instead of the capacity spectrum method applied in HAZUS, building response is estimated by inelastic response history analysis of corresponding single-degree-of-freedom systems under a large number of earthquake records. Statistics of the building response are used with the damage state definitions from HAZUS to derive fragility models conditioned on spectral acceleration values. Using the developed fragility models for structural and nonstructural building components, with corresponding damage state loss ratios from HAZUS, we also derive building vulnerability models relating spectral acceleration to repair costs. Whereas in HAZUS the structural and nonstructural damage states are treated as if they are independent, our vulnerability models are derived assuming "complete" nonstructural damage whenever the structural damage state is complete. We show the effects of considering this dependence on the final vulnerability models. The use of spectral acceleration (at selected vibration periods) as the ground motion intensity parameter, coupled with the careful treatment of uncertainty, makes the new fragility and vulnerability models compatible with conventional seismic hazard curves and hence useful for extensions to probabilistic damage and loss assessment.

Conference Paper↗

USGS2007

Influence of light and temperature on Prochlorococcus ecotype distributions in the Atlantic Ocean

In a focused analysis of Prochlorococcus population structure in the western North Atlantic, we found that the relative abundances of ecotypes varied significantly with depth and, at seasonally stratified locations, with degree of vertical mixing. More limited regional variation was observed (e.g., Sargasso Sea, Gulf Stream, continental slope, and equatorial current), and local patchiness was minimal. Modeling of a combined North and South Atlantic data set revealed significant, independent effects of light and temperature on ecotype abundances, suggesting that they are key ecological determinants that establish the different habitat ranges of the physiologically and genetically distinct ecotypes. This was in sharp contrast with the genus Synechococcus, whose total abundance was related to light but did not vary in a predictable way with temperature. Comparisons of field abundances with growth characteristics of cultured isolates of Prochlorococcus suggested the presence of ecotype-specific thermal and light adaptations that could be responsible for the distinct distribution patterns of the four dominant ecotypes. Significantly, we discovered that one "low-light-adapted" ecotype, eNATL2A, can thrive in deeply mixed surface layers, whereas another, eMIT9313, cannot, even though they have the same growth optimum for (low) light. ?? 2007, by the American Society of Limnology and Oceanography, Inc.

Limnology and Oceanography↗