U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3094

July 2012

Helping Safeguard Veterans Affairs’ Hospital Buildings by Advanced Earthquake Monitoring 

The integrity of the Nation’s hospitals is vital for the survival and functioning of the society in the aftermath of a catastrophic earthquake.

I

n collaboration with the U.S. 

Department of Veterans Affairs (VA), 

the National Strong Motion Project of 

the U.S. Geological Survey has recently 

installed sophisticated seismic systems 

that will monitor the structural integrity 

of hospital buildings during earthquake 

shaking. The new systems have been 

installed at more than 20 VA medical 

campuses across the country. These 

monitoring systems, which combine 

sensitive accelerometers and real-time 

computer calculations, are capable of 

determining the structural health of each 

structure rapidly after an event, helping to 

ensure the safety of patients and staff.

Department of

Veterans Affairs

Department of

Veterans Affairs

Following the 1971 magnitude 6.6 San 

Fernando earthquake in Southern California, 

which resulted in the collapse of several 

hospital buildings, the U.S. Department of 

Veterans Affairs (VA) established its Seismic 

Vulnerability Assessment Program to 

identify and strengthen VA hospital buildings 

that needed to be brought up to acceptable 

seismic safety standards. An important 

component of this program is monitoring 

earthquake shaking in hospital buildings. 

Shortly after the 1971 earthquake, the U.S. 

Geological Survey (USGS) collaborated with 

the VA on installing analog accelerographs 

in 60 VA hospital buildings across the 

country. These accelerographs were mostly 

placed on the base level of the buildings. 

Because these instruments recorded on 

photographic film, it often took many days 

or even weeks after an earthquake to process 

and analyze the records. Later, in 2003, 45 of 

these seismic monitoring instruments were 

replaced by modern digital systems. Since 

2008, more than 20 VA medical centers 

have been instrumented with sophisticated 

arrays of seismic motion sensors to better 

understand their response to strong ground 

shaking during earthquakes. Today, the USGS 

National Strong Motion Project (NSMP) 

works closely with the VA to monitor 

earthquake shaking in more than 70 of their 

medical centers in earthquake-prone regions 

across the counterminous United States, in 

Alaska, and in Puerto Rico. These monitored 

structures are part of a larger network of 

more than 250 structures instrumented under 

the USGS Advanced National Seismic 

System (ANSS), which is modernizing and 

expanding earthquake monitoring around the 

Nation to improve the overall understanding 

of earthquakes and their effects on the 

built environment. Data recorded by these 

instruments will enable improvement of 

building design to create more resilient and 

safer structures that can better protect people 

and resources. 

Monitoring Earthquake Shaking at 

VA Medical Centers

An important goal of VA hospitals 

is to be able to continue to operate and 

serve the patient community after 

a major earthquake. However, the 

building itself may have been damaged 

and, consequently, may pose a hazard 

to patients and staff. It is critical that 

hospital management have the tools and 

information necessary to make a rapid 

decision whether to evacuate or not. 

Early assessment of the integrity of the 

hospital buildings affected by the quake is 

valuable in this decisionmaking process. 

For resilience and sustainability of the 

Nation’s hospitals, it is also necessary 

to assess their structural condition 

periodically in order to facilitate necessary 

repairs and retrofitting measures. 

In the San Diego,

California, VA 

Medical Center,

the recently 

retrofitted 

main hospital 

building(shown 

in inset photo) 

is being equipped with advanced earthquake 

monitoring systems. Red arrows in the schematic 

diagram show the locations and indicate 

the directional sensitivity of the seismic 

sensors from the basement through the 

building’s seven stories to the roof. The 

triaxial sensor on the ground floor (at 

lower right) monitors the input motions in 

three orthogonal directions.

Flow chart showing the functioning of a real-time earthquake monitoring system for instrumented buildings. 

The system provides important information on the structural health of the building. After a significant 

earthquake, its near-real-time data analysis capabilities help to rapidly assess building safety.

Sensors

Data acquisition/analysis system

Smartphone alerts

Data to the internet

Access data via internet

Damage detection

Data Alarm

Drift computation

Shear wave computation

Base shear computation
Erol Kalkan1

, Krishna Banga2, Hasan S. Ulusoy3, 

Jon Peter B. Fletcher1, William S. Leith4, and

James L. Blair1

Edited by Peter H. Stauffer

Graphic design by Jeanne S. DiLeo

COOPERATING ORGANIZATIONS

U.S. Department of Veterans Affairs

For more information, contact:

Earthquake Science Center

U.S. Geological Survey

Menlo Park, CA 94025

http://earthquake.usgs.gov/

Earthquake Information Hotline: (650) 329–4085

This Fact Sheet and any updates to it are 

available online at:

http://pubs.usgs.gov/fs/2012/3094/

In response to these needs, the VA 

Seismic Vulnerability Assessment Program, 

together with the USGS NSMP, created 

a new initiative in 2008 to develop an 

advanced earthquake monitoring system for 

VA medical centers. This advanced system 

has two parts—sensing and analysis. The 

sensing part comprises a dense array of motion 

sensors, installed permanently at each floor 

of a building, and rapid data transmission and 

acquisition. The analysis part consists of several 

data processing modules integrated into an 

open-source software package that compresses 

a large amount of measured data into useful 

information for assessing the condition of a 

building before and after an earthquake. 

The USGS has already instrumented 21 

VA hospital buildings located in quake-prone 

regions across the country (see map) with 

sophisticated systems of multiple seismic 

motion sensors, and similar instrumentation 

is planned at 7 additional hospital buildings. 

The number of sensors deployed in each 

building varies, depending on the floor area, 

the number of stories, and the number of 

blocks (or wings) in the building. For instance, 

the main hospital building at the VA medical 

center in San Diego, California, will have a 

seismic array of 60 sensors. Locations for these 

sensors are strategically selected where the 

maximum response is expected, mostly at the 

edges of floors. Every story in each similarly 

instrumented building has at least three seismic 

motion sensors oriented horizontally in two 

orthogonal directions to detect building motion 

along the reference east-west and north-south 

directions. Floor rotation around the vertical 

axis can be computed from the recordings of 

sensors located at different points. Each building 

also has a triaxial sensor located on the ground 

floor, which records the input motions in three 

orthogonal directions at this level. Additional 

vertically oriented sensors allow the building’s 

rocking motions to be computed. Specifically, 

the instrumentation within each building is 

designed to record:

• the swaying and twisting of the building, 

• the time it takes seismic waves to travel from 

the foundation to the roof, and 

• how the frame of the building changed during 

the earthquake. 

Other seismic motion sensors located 

away from the building record free-field ground 

shaking, which provides input for USGS 

Shakemaps. These computer-generated graphics 

depict ground motion and shaking intensity after 

significant earthquakes, giving a quick visual 

representation of a quake’s shaking behavior for 

emergency response. 

Assessing a Building’s Structural 

Health and Detecting Damage 

After a major earthquake it is imperative 

to monitor the condition of hospital buildings 

in near-real time in order to be able to 

assess their structural integrity immediately. 

Structural health monitoring is achieved by 

the array of sensors in the building and an 

open-source on-site data analysis system. This 

innovative system provides information about 

how buildings move and distort during shaking 

and where possible damage likely occurred. 

Several independent algorithms check for 

variations in movements of a building frame 

and its vibration characteristics, for travel time 

of seismic waves between foundation and roof, 

and for exceedance of the building’s seismic 

design capacity. If the damage detection 

algorithms agree, alarm messages are sent (see 

the flow chart on previous page). 

 This information allows rapid 

assessment of building safety in the aftermath 

of a major quake and supports decisions about 

necessary repairs, replacements, and other 

maintenance and rehabilitation measures. 

In the long run, this system also monitors 

the building’s structural components for 

indications of deterioration and fatigue, 

enabling the building to be made more 

resilient and sustainable through improved 

maintenance. Recordings from structuralhealth monitoring systems are critical to 

designing safer hospitals and other buildings 

and to preventing loss of life. In particular they 

will help engineers to: 

• assess building safety immediately 

following a damaging quake,

• understand how damage to structural 

and nonstructural components (such as 

equipment and pipes) occurs from strong 

shaking,

• evaluate and improve earthquake-resistant 

design techniques and also methods for 

predicting the seismic performance of 

structures, and

• improve earthquake-resistant design 

provisions of building codes.

These efforts in turn will help the 

U.S. Department of Veterans Affairs 

safeguard its building inventory from 

future earthquake losses. 

Seismic hazard map of the conterminous United States, Alaska, and Puerto Rico, showing the locations of 28 

VA medical centers (black dots)—21 of these are already equipped with advanced earthquake monitoring 

systems, and the remainder will be by the end of 2013. Most of these hospital buildings are located in regions 

of high or very high seismic hazard. By placing shaking sensors in hospital buildings in quake-prone regions 

of the country, the U.S. Geological Survey and VA are acquiring data critical for reducing future losses arising 

from structural damage and collapse. (The seismic hazard map is at http://pubs.usgs.gov/fs/2008/3018/.)

Hazard

HIGH

LOW

Alaska Puerto Rico

1

U.S. Geological Survey, Menlo Park, Calif.

2

U.S. Department of Veterans Affairs, Washington, D.C.

3

22 Coleman Avenue, Menlo Park, Calif.

4

U.S. Geological Survey, Reston, Va.