Seismic Response of a Tall Building to Recorded and Simulated Ground Motions

Seismological modeling technologies are advancing to the stage of enabling fundamental simulation of earthquake fault ruptures, which offer new opportunities to simulate extreme ground motions for collapse safety assessment and earthquake scenarios for community resilience studies. With the goal toward establishing the reliability of simulated ground motions for performance-based engineering, this paper examines the response of a 20-story concrete moment frame building analyzed by nonlinear dynamic analysis under corresponding sets of recorded and simulated ground motions. The simulated ground motions were obtained through a larger validation study via the Southern California Earthquake Center (SCEC) Broadband Platform (BBP) that simulates magnitude 5.9 to 7.3 earthquakes. Spectral shape and significant duration are considered when selecting ground motions in the development of comparable sets of simulated and recorded ground motions. Structural response is examined at different intensity levels up to collapse, to investigate whether a statistically significant difference exists between the responses to simulated and recorded ground motions. Results indicate that responses to simulated and recorded ground motions are generally similar at intensity levels prior to observation of collapses. Collapse capacities are also in good agreement for this structure. However, when the structure was made more sensitive to effects of ground motion duration, the differences between observed collapse responses increased. Research is ongoing to illuminate reasons for the difference and whether there is a systematic bias in the results that can be traced back to the ground motion simulation techniques

Classification algorithms for collapse prediction of tall buildings and regional risk estimation utilizing SCEC CyberShake simulations

Quantification of collapse risk of buildings in seismically active regions is one of the key elements for informed decision making for building design and establishment of public policies to promote seismic safety and resilience. This paper focuses on development, testing and application of efficient and reliable collapse classification algorithms using machine learning tools. To this end, a large database of structural responses is developed by performing around two million nonlinear time history analyses of an archetype 20-story tall building. Unscaled seismograms simulated for the Los Angeles region as part of the Southern California Earthquake Center (SCEC) CyberShake project are used as inputs for the analysis. Feature selection is performed using regularized logistic regression to identify intensity measures with strong predictive power for classification of collapse. Results of regularization generally confirm the understanding of important predictors as gained from scaling of recorded motions as well as highlight additional important features. Logistic regression and support vector machine (SVM) binary classifiers are then trained on the data to develop collapse prediction models. The resulting collapse assessment models achieve high values of precision and recall and show good performance when tested using benchmark collapse responses. Finally, trained collapse classifiers are utilized to perform regional estimation of collapse risk. Collapse predictions are made using CyberShake data from 336 sites across Southern California where there are around 500,000 simulated seismograms at each site. Regional estimation of mean annual frequency of collapse is performed to generate maps of collapse risk. Higher values of risk correlate well with geologic features such as presence of sedimentary basins and the surface trace of the San Andreas fault

Petrinja, Croatia December 29, 2020, Mw 6.4 Earthquake Joint Reconnaissance Report (JRR)

On December 29, 2020 a magnitude 6.4 earthquake occurred in the Sisak-Moslavina county of Croatia. The earthquake occurred along the Popusko-Petrinja strike slip fault within the Eurasia plate at a depth of 10 km with an epicenter at 45.422°N 16.255°E, three kilometers (km) west-southwest of the city of Petrinja. The maximum intensity of the earthquake was VII (severe) on the Modified Mercalli Intensity (MMI) scale and VIII (heavily damaging) to IX (destructive) on the European Macroseismic Scale (EMS). Due to the earthquake and resulting damage, there were seven fatalities, 26 people were injured, and many hundreds of people were displaced from their homes. The most affected city was Petrinja, but severe damage also occurred in Sisak, Dvor, Glina, Topusko, as well as in Croatia’s capital Zagreb, located approximately 50 km northwest of the epicenter. Damage was also reported in neighboring countries, including Slovenia, located north of Croatia, and Bosnia and Herzegovina, located south of this region of Croatia. The purpose of this post-earthquake reconnaissance report is to provide, within a few days of the earthquake, an overview of the hazard characteristics and to summarize preliminary reports of damage to buildings, bridges, roads, and other infrastructure. Moreover, key findings are also summarized with regard to geotechnical failures that include liquefaction, lateral spreading, landslides, sinkholes and damage to the extended levee system along the Kupa, Odra and Sava rivers