By Leonid Zimakov, PhD
According to the United States Geological Survey (USGS), 42 of 50 states “have a reasonable chance of experiencing damaging ground shaking from an earthquake.” In addition, 16 states have a “relatively high likelihood” of damaging shaking.
What does this mean to the safety of your building? Logically, much of the answer varies from state to state. California has the most risk associated with earthquake damage, and in line with that, is currently the only state that has seismic monitoring requirements in the city building codes for Los Angeles and San Francisco. While Washington and Oregon do not have compulsory seismic instrumentation in their state building codes, they do have published recommendations. Other states rely on architects and structural engineers to develop a shake-resistant structural design built with suitable materials to withstand a low or moderate magnitude earthquake (with Peak Ground Acceleration of hazard zone 4 or greater) or other seismic activity that can occur due to nearby construction or other natural occurrences.
Before 2007, California, like Washington and Oregon today, only had recommendations for seismic monitoring of buildings. Following a series of large earthquakes in the Los Angeles and San Francisco areas in the mid-1990s, and a public awareness campaign highlighting concern for “the next big one,” the recommendations were changed to requirements. These building code specifications apply to any building built after July 1965, with six or more stories and an aggregate square footage of 60,000 or more, or any building more than 10 stories. The requirements outline the minimum instrumentation and components, as well as approved building materials and structural systems.
The monitoring instrumentation includes three accelerometers that are placed in the basement, the midpoint, and the top of a building, either on the top floor or the roof. These accelerometers deliver data for professional engineers and building owners to help assess whether the structure is safe to occupy after an earthquake or other seismic event. After any shake event, California city building authorities may request a Shake Event Report. The Hardware Compliance Report must be submitted every 12 months, requiring the building owner to test the structure’s monitoring systems to ensure they are working correctly. This test can be conducted by a certified test agency such as the monitoring solution manufacturer or the California Geological Survey (CGS).
High-rise buildings more than 10 stories have even stricter guidelines that recommend providing additional channels of reporting in proportion to the number of stories in the building. Buildings critical to life and safety (e.g., federal and state buildings, and hospitals) are generally instrumented directly by the CGS. To date, only two monitoring solution providers are approved to provide equipment for these types of buildings.
An inventory conducted in Los Angeles found more than 600 structures requiring seismic monitoring; today, these buildings have been notified they must meet compliance by submitting an annual Hardware Compliance Report. If a structure is found non-compliant, the owner is sent a violation notice and given a specific period in which they must comply with the seismic instrumentation code. If they do not comply, they are fined. The fine increases every six months thereafter until the code is satisfied.
If a building owner needs to implement a new monitoring solution post-construction, the first step is to contact an approved solution provider that meets the instrumentation requirements to satisfy the seismic monitoring building code. A list of these providers can be obtained from the city’s building department.
Seismic Code Compliance
Seismic monitoring equipment is best installed near construction completion. At this point, the electrical contractor or construction company will purchase the equipment to be installed. Many of the systems’ sensors are placed above the ceilings, and the conduits and cables connecting the sensors are behind the walls, so it’s logical to install the equipment before a building is complete.
In most cases, it is challenging to install new equipment or replace outdated equipment after a structure is built. This challenge applies to any structure once completed, whether it is a two-year old building or more than 50 years old. Structures built around 50 years ago, or even as recent as 11 years ago, may not have had any seismic monitoring instrumentation, so they would face a more significant challenge to install a new system, and all the necessary cables and wiring. For structures with instrumentation already in place, it is possible it wouldn’t be as difficult if all the cables and wiring are already in place and up-to-date.
With all the seismic monitoring systems hidden from sight, ceilings and walls must be opened, and there is the potential need for adding new cables or additional conduits. Whether inserting new equipment to meet code or replacing an old system whose parts are no longer available for repair, it is a costly process.
Monitoring A Building’s Health
Several systems monitor a building’s health, especially in high-rise structures greater than 10 stories. From temperature to wind to high-resolution seismic strong motion sensors, it is essential to keep watch on a building’s welfare to protect its occupants, those living and working around the building, the structure itself and the surrounding infrastructure. Large magnitude earthquakes can cause significant damage in a small amount of time, however smaller magnitude earthquakes can cause damage to buildings that often goes unnoticed until it’s too late.
Implementing seismic monitoring equipment on buildings in earthquake-prone zones makes sense for safe post-shake occupancy. Luckily, however, there is a dedication from architects and structural engineers to design buildings and use materials that will withstand a certain amount of shaking. In areas where building code does not have any seismic monitoring requirements or recommendations, the architect or engineer may choose to incorporate seismic monitoring instrumentation within the design plans. To receive a certificate of occupancy, the building must be built to meet the design plans as signed off by the owner.
Surprisingly, in some states seismic monitoring systems are frequently found on bridges, but not in buildings. This tactic makes sense when considering the materials used for bridges, which are not held to the same level of stability as for building construction.
Whether you live in California or any other state, it is essential to take the time to find out what, if any, seismic monitoring building codes exist. If you discover there aren’t any seismic monitoring building codes in place, talk with your building’s architect or structural engineer about the potential damage from seismic activity to the population, structures, and infrastructure and whether your building can stand the shake.
Zimakov is a seismic market manager for REF TEK®, a Trimble brand. During the last 40 years as a seismologist, he has conducted research on earthquake prediction and remote earthquake triggering, managed geophysical networks, and has been responsible for sales and marketing of monitoring solution products. Leonid earned a bachelor of science in geophysics and seismology from Lomonosov Moscow State University, a master of science in geophysics from Moscow State University and conducted his postdoctoral research program at the University of Michigan.