Earthquake Engineering - Vibrationdata Engineering Blog

High-Frequency Seismic Content & Substation Equipment

July 23, 2026July 23, 2026 by Tom Irvine

A recurring question in Central and Eastern North America (CENA) seismic qualification goes something like this: the site-specific ground motion exceeds the IEEE 693 required response spectrum above 10 Hz, sometimes by a factor of two to four. Does that mean the equipment is unqualified?… Read more

The 2026 Venezuela Earthquake Doublet

July 23, 2026July 10, 2026 by Tom Irvine

On the evening of 24 June 2026, northern Venezuela was struck by two major earthquakes 39 seconds apart — a rare “doublet” that became the country’s deadliest natural disaster in a generation. For the structural dynamics community, the event is a case study in nearly… Read more

Seismic Time History & Response Spectrum Debate

July 23, 2026June 5, 2026 by Tom Irvine

San Mateo Bridge, Highrise Section, San Francisco Bay Area UC Berkeley Professor Ed Wilson raised a pointed concern about the Response Spectrum Method (RSM) that structural engineers should take seriously. In his 2015 note, he described the San Mateo Bridge retrofit as a revealing case… Read more

Equipment Racks & Earthquakes

July 23, 2026October 22, 2025 by admin

Seismic-restrained Isolators The following is an edited response from ChatGPT. Resonant response of the equipment rack circuit boards should not be an issue, because circuit board fundamental frequencies are typically above 200 Hz, whereas seismic energy is mostly below 20 Hz. But electronic components may… Read more

Waterfall SRS, 1940 El Centro Quake

July 23, 2026April 2, 2017 by admin

The top figure is the time history from the El Centro earthquake, North-South horizontal component. The middle is the corresponding Waterfall SRS with 4 second segments and with 50% overlap. The bottom is the spectrogram. The Waterfall SRS is calculated by first taking the complete… Read more

Tom’s Conference Papers & Slide Index

March 8, 2017 by admin

I am trying to collect all my presentations. This is a work-in-progress… Thank you, Tom Irvine * * * * * * NAFEMS World Congress 2017 Introduction to Vibration Spectral Functions Random Vibration Vibration Fatigue Shock 1 & 2 Videos * * * * *… Read more

Multi-axis Shock & Vibration Testing

July 23, 2026February 1, 2017 by admin

Equipment must be designed and tested to withstand shock and vibration. Ideally, all equipment would be tested on a shaker table with six-degree-of-freedom control (three translations and three rotations). Such tables and control systems exist but are very expensive. Furthermore, any multi-axis testing requires careful… Read more

Seismic Test & Analysis Webinars

December 29, 2016 by admin

This is a work-in-progress… I am creating a series of webinars with Matlab exercises for seismic testing. Here are the slides. Telcordia Technologies Generic Requirements GR-63-CORE: Bellcore_GR_63_Core.ppt This unit contains an alternative waveform for VERTEQII. CEI.IEC 980, Recommended practices for seismic qualification of electrical equipment… Read more

Hypersphere SRS

July 23, 2026July 16, 2016 by admin

Figure 1. El Centro Earthquake 1940, Peak Pseudo Velocity, 36.4 in/sec Launch vehicle and spacecraft equipment must withstand pyrotechnic shock from stage separation and other flight events. Civil engineering structures and equipment must survive seismic events. There are many other examples where military, automotive,… Read more

Energy Response Spectrum

October 13, 2015 by admin

My colleagues at Sandia National Laboratories have presented some conference papers recently on energy response spectrum. Here is a paper that I wrote on this topic: energy_response_spectrum.pdf Also, I have added the energy response spectrum as an option for acceleration time histories to the Vibrationdata… Read more