Geology topics

Hamid Haddadi

Publications and source records attributed to Hamid Haddadi.

8 recordsLinked to original sources

USGS2024

Performance-based earthquake early warning for tall buildings

The ShakeAlert Earthquake Early Warning (EEW) system aims to issue an advance warning to residents on the West Coast of the United States seconds before the ground shaking arrives, if the expected ground shaking exceeds a certain threshold. However, residents in tall buildings may experience much greater motion due to the dynamic response of the buildings. Therefore, there is an ongoing effort to extend ShakeAlert to include the contribution of building response to provide a more accurate estimation of the expected shaking intensity for tall buildings. Currently, the supposedly ideal solution of analyzing detailed finite element models of buildings under predicted ground-motion time histories is not theoretically or practically feasible. The authors have recently investigated existing simple methods to estimate peak floor acceleration (PFA) and determined these simple formulas are not practically suitable. Instead, this article explores another approach by extending the Pacific Earthquake Engineering Research Center (PEER) performance-based earthquake engineering (PBEE) to EEW, considering that every component involved in building response prediction is uncertain in the EEW scenario. While this idea is not new and has been proposed by other researchers, it has two shortcomings: (1) the simple beam model used for response prediction is prone to modeling uncertainty, which has not been quantified, and (2) the ground motions used for probabilistic demand models are not suitable for EEW applications. In this article, we address these two issues by incorporating modeling errors into the parameters of the beam model and using a new set of ground motions, respectively. We demonstrate how this approach could practically work using data from a 52-story building in downtown Los Angeles. Using the criteria and thresholds employed by previous researchers, we show that if peak ground acceleration (PGA) is accurately estimated, this approach can predict the expected level of human comfort in tall buildings.

Earthquake Spectra↗

USGS2024

New developments at the Center for Engineering Strong-Motion Data (CESMD)

The Center for Engineering Strong-Motion Data (CESMD), an internationally utilized joint center of the U.S. Geological Survey (USGS) and the California Geological Survey (CGS), provides a single access point for earthquake strong-motion records and station metadata from the CGS California Strong-Motion Instrumentation Program (CSMIP), the USGS National Strong-Motion Project (NSMP), the USGS Advanced National Seismic System, and other affiliates. The CESMD has been continuously improving its webtools to facilitate the access of strong-motion data and metadata for use in post-earthquake response and for scientific and engineering research applications. The Center provides raw and processed strong-motion data via the Engineering Data Center (EDC) and the Virtual Data Center (VDC) web portals. This paper focuses on the strong-motion products provided by the EDC where more than 48,000 records with peak ground accelerations greater than 0.1% g from over 2400 earthquakes are currently hosted. and on the ongoing efforts to develop data access tools and applications. The new developments and ongoing efforts in the EDC include: 1) enhancements to the CESMD webservices to facilitate access to station metadata, earthquake information, and strong motion records 2) new features to the interactive map interface, improving the visualization and access to earthquake, station, and record information, 3) efforts to develop a new web application tool for data format conversion from a number of data formats, 4) efforts to unify varying waveform data formats into a consistent format, 5) ongoing efforts to compile seismic station site geology, measured or inferred Vs30 values, shear-wave profiles, NEHRP site class, and available structural instrument deployment schematics, and 6) a special studies pages for research topic-specific ground motion datasets that offer uniform processing of records from a variety of sources.

Conference Paper↗

USGS2021

Response study of a 51-story-tall Los Angeles, California building inferred from motions of the Mw7.1 July 5, 2019 Ridgecrest, California earthquake

A 51-story building in downtown Los Angeles that is equipped with a seismic monitoring accelerometric array recorded the Mw7.1 Ridgecrest, California earthquake of July 5, 2019. The building is a dual-core reinforced-concrete shear-wall and perimeter-column structure with ~ 80% of floors constructed as post-tensioned flat slabs, which makes it a trending design. Using system identification methods, spectral analyses, and coherence-phase angle computations, the recorded response data allowed the identification of dynamic response characteristics (fundamental frequencies of [NS] 0.21 Hz, [EW] 0.28 Hz, and [Torsional] 0.45 Hz, critical damping percentages < 2.5%, and associated mode shapes), as well as computation of drift ratios with maximum peaks of 0.145% for both NS and EW directions. The critical damping percentages are consistent with those recommended by LATBSDC ( 2017 ). There is no indication from the records that post-tensioned slab design played any role in altering the dynamic characteristics.

California↗

USGS2020

Response study of the tallest California building inferred from the Mw7.1 Ridgecrest, California earthquake of 5 July 2019 and ambient motions

The newly constructed tallest building in California, the 73-story Wilshire Grand in Los Angeles, California, is designed in conformance with performance-based design procedures. The building is designed with concrete core–shear walls, three outriggers with buckling restrained braces (BRBs) located along the height, and two three-story truss-belt structural systems. The building is equipped with a 36-channel accelerometric seismic monitoring array that recorded the recent Mw7.1 Ridgecrest earthquake of 5 July 2019, as well as the Mw6.4 Ridgecrest earthquake of 4 July 2019. In this article, only the Mw7.1 event of 5 July 2019 is studied because of a larger response of the subject building during that earthquake. The earthquake records of 5 July 2019 are specifically studied to determine its dynamic characteristics and building-specific behavior. The structure exhibits torsional behavior most likely due to abrupt asymmetrical changes in the thickness and size in-plan of the core–shear walls. The translational and torsional modes during the earthquake are not closely coupled, which does not lead to a beating effect even though there is an appearance of it in the records. Available ambient records are used only to identify modal frequencies of the building and compare them with those from the Mw7.1 event of 5 July 2019. Due to the relatively low amplitude of shaking during the earthquake, the drift ratios are too small to cause any damage. It is expected that during stronger shaking levels likely to be caused by future events, these characteristics may change and the effect of BRBs can be better assessed.

California↗

USGS2020

Response of the tallest California building during the Mw7.1 July 5, 2019 Ridgecrest, California earthquake

The 73-story Wilshire Grand in downtown Los Angeles is the recently constructed tallest building in California. It is designed in conformance with performance-based design procedures. The lateral load resisting system of the building is designed with concrete core shear walls, three outriggers with buckling restrained braces (BRBs) located along the height and two three-story truss-belt structural systems. The building is equipped with a 36-channel accelerometric seismic monitoring array that recorded the recent Mw7.1 Ridgecrest earthquake of July 5, 2019, as well as the Mw6.4 July 4, 2019 Ridgecrest Earthquake. In this paper, only the Mw7.1 July 5, 2019 event is studied because of a larger response of the subject building during that earthquake. The earthquake records of July 5, 2019 are specifically studied to determine its dynamic characteristics and building specific behavior. The structure exhibits torsional behavior most likely due to abrupt asymmetrical changes in the thickness and size in-plan of the core shear wall system. Modal shapes, frequencies and critical damping percentages of the building are identified. The translational and torsional modes during the earthquake are not closely coupled with fundamental NS, EW and torsional frequencies (periods) of 0.16 (6.25), 0.27(3.70) and 0.42 (2.38) Hz (seconds). This does not lead to a beating effect even though there is an appearance of it in the displacement records. Due to the relatively low amplitude of shaking during the earthquake, the drift ratios are too small to cause any damage. It is expected that during stronger shaking levels likely to be caused by future events, these characteristics may change and the effect of BRB’s can be better assessed.

California↗

USGS2019

The behavior of the Salesforce Tower, the tallest building in San Francisco, California inferred from earthquake and ambient shaking

The newly constructed tallest building designed in conformance with performance-based design procedure in San Francisco, California is a 61-story building equipped with an accelerometric array that recorded the January 4, 2018 M4.4 Berkeley earthquake. The building is designed with concrete core shear walls and perimeter gravity steel columns. The earthquake records as well as on-demand recorded ambient responses of the building are studied to determine its dynamic characteristics and building-specific behavior. At the level of shaking of either the earthquake or ambient excitation, the frequencies and low modal damping ratios (<2%) are similar. The building exhibits torsional behavior most likely due to abrupt asymmetrical changes in the size of the core shear wall. The translational and torsional modes during the earthquake are closely coupled, which leads to a beating effect, the period of which is calculable. Due to the relatively low-amplitude shaking during the earthquake, the drift ratios were small and did not cause any damage. It is expected that during stronger shaking levels, these characteristics may change.

California↗

USGS2008

The Virtual Data Center Tagged-Format Tool: Introduction and executive summary

This Report introduces and summarizes the new Virtual Data Center (VDC) Tagged Format (VTF) Tool, which was developed by a diverse group of seismologists, earthquake engineers, and information technology professionals for internal use by the COSMOS VDC and other interested parties for the exchange, archiving, and analysis of earthquake strong-ground-motion data.

Open-File Report↗

USGS2005

Preliminary analysis of strong-motion recordings from the 28 September 2004 Parkfield, California earthquake

The 2004 M w 6.0 Parkfield earthquake of 28 September 2004 occurred on the San Andreas Fault near the small town of Parkfield in central California. As a result of a widely accepted likelihood of an earthquake in the area, a large number of strong-motion stations and other types of seismic stations had been deployed in the area. The Parkfield earthquake occurred along the same segment of the San Andreas Fault that ruptured during the 1966 Parkfield earthquake, resulting in a unique set of strong-motion measurements by arrays designed specifically for the purpose of recording an event along this fault segment. The most extensive and dense set of near-fault strong-motion recordings yet obtained for any earthquake in California was obtained in this event. This paper provides a detailed description of the arrays and the resultant strong-motion measurements of the mainshock, as well as preliminary observations. We also invite interested parties to participate in the Turkey Flat blind prediction experiment, described later in the paper. More general preliminary seismological results for this earthquake can be found in Langbein et al. ( 2005 , this issue).

California↗