Are YOU Safe From Earthquakes? Take This Quiz!

This article is provided by Ali Sahabi, Chief Operating Officer, Optimum Seismic

Geological and Structural Risks Make Your Apartment Building Vulnerable to Damages.

Californians think they know a lot about earthquakes.  We should. Earthquakes are a recurring threat in our state, and most of us have lived through at least one significant earthquake that left us shaken and with stories we readily share.

But how much do we really know about the many risks that earthquakes present to us? Understanding these threats and the numerous factors that increase those dangers is important, particularly when buildings are essential to your livelihood. Wonder how much you really know? Try taking this little quiz, for starters.

Optimum’s QUIZ: The Questions

1. What is the most dangerous region in the United States for projected earthquake loss?

a.Seattle

b. San Francisco

c. Los Angeles

d. Charleston, SC

e. San Bernardino

2. What are the odds that a major earthquake will strike in the next 30 years?

a. 7% chance of a quake equal to or larger than Northridge hitting California

b. 59% chance of such a quake (6.7 magnitude) striking the southern San Andreas

c. 46% likelihood of a magnitude 7 hitting L.A.

d. 31% chance of a magnitude 7.5 – a colossal quake – striking Los Angeles

3. How many buildings would be damaged in a 7.8 earthquake, according to the United States Geological Survey (USGS)?

a. 1 in 8

b. 1 in 16

c. 1 in 350

d. 1 in 1,500

e. 1 in 3,500

4. What is the primary earthquake risk indicator for soft-story apartment buildings?

a. Number of stories

b. Building value

c. Year of construction

d. Proximity to an earthquake fault

5. Soil conditions is another indicator of earthquake hazard. Which of these is considered to present the highest risk?

a. Solid bedrock

b. Sandstone

c. Mud

d. Alluvial soils

Optimum’s QUIZ: The Answers

1. The answer is “” The Federal Emergency Management Agency’s HAZUS annualized earthquake loss risk projections put seven California areas in the nation’s Top-10 list with Los Angeles / Long Beach/Anaheim ranked number One. Other high risk areas are: (#2) San Francisco / Oakland / Hayward; (#3) Riverside / San Bernardino / Ontario; (#4) San Jose / Sunnyvale / Santa Clara; (#5) Seattle / Tacoma / Bellevue; (#6) Portland / Vancouver / Hillsboro; (#7) San Diego / Carlsbad; (#8) Oxnard / Thousand Oaks / Ventura; (#9) Santa Rosa; and (#10) Charleston[i].

2. The answer is “all of the above.” (Yes, it was a trick question…we only asked one like this.) The numbers for earthquake probability are all over the map, depending on the location and magnitude of the projected threat. The most comprehensive statewide analysis of earthquake probabilities determined the chance of having one or more magnitude 6.7 or larger earthquakes in California over the next 30 years is 99.7%, according to the U.S. Geological Survey. The fault with the highest probability of such earthquakes is the southern San Andreas — 59% in the next 30 years. For powerful quakes of magnitude 7.5 or greater, there is a 37% chance that one or more will occur in the next 30 years in Southern California, according to the Earthquake Country Alliance, an organization comprised of the National Earthquake Hazards Reduction Program, the Federal Emergency Management Agency, the California Governor’s Office of Emergency Services, and the Southern California Earthquake Center (a joint venture of the National Science Foundation and United States Geological Survey).

3. The answer is “B.” Based on the type of construction and the building code at the time when they were built, we have a pretty good understanding of what buildings are likely to be damaged in future earthquakes. A detailed scientific assessment of likely damage in a big San Andreas earthquake in Southern California[ii] estimated that 300,000 buildings in Southern California would be damaged at a moderate level (losing at least 10% the value of the building) as modeled in the simulated magnitude 7.8 Shake-Out scenario earthquake. This represents 1 out of every 16 buildings in the region. Moreover, about 1,500 of those buildings will collapse.

4. The answer is “C.” Soft-story buildings are easily identified as upper-story dwelling units built over open parking areas on the ground floor. The fatal collapse of the Northridge Meadows apartment complex in 1994 revealed serious design flaws in buildings of this type constructed before 1978. Therefore, year of construction is the primary risk indicator for earthquake damage for this type of structure. Proximity to an earthquake fault is another factor in calculating risk for these types of buildings, but soft story structures constructed after 1978 are not generally considered high-risk, due to improvements made in the structural design of those newer buildings.

5. The answer is “D.” Alluvial soils. Soil type is a key factor in assessing earthquake vulnerability because the density of the ground has a direct effect on the amount of motion the ground will experience during a quake. Hard ground propels the seismic energy quickly with a small amplitude, while soft ground slows the energy down and increases the amplitude or severity of the motion. The U.S. Geological Survey has ranked the following soil types for susceptibility to strong ground movement from an earthquake, with solid bedrock (both igneous and volcanic) as the least susceptible, and alluvial soils and artificial fill as the most[iii].

 What are alluvial soils? About 15 million years ago, the Los Angeles Basin was underwater. Over the span of many millennia, surrounding mountain ranges rose, releasing molten rock into the underlying crust to create an immense geologic bowl that time filled with sand, silt, and clay from ancient rivers. Today, the basin represents home to millions of people living and working in 80 communities from Santa Monica to the San Gabriel Valley, and from Hollywood to north Orange County. These soil conditions are prone to a phenomenon known as liquefaction – which can significantly intensify the damage to buildings in an earthquake. Liquefaction happens when vibrations in the ground cause soil particles to lose contact with each other – causing the ground to react to seismic vibrations like a liquid, vibrating and undulating like Jell-O to significantly increase the potential for damage to a building. Visit maps.conservation.ca.gov/cgs/EQZApp/app/ and zoom in to view the California Geological Survey’s earthquake hazard map for Greater Los Angeles region.

There are many factors to consider when weighing your earthquake risks and the benefits of strengthening your building. If you have questions, contact Optimum Seismic at (833) 978-7664 or visit optimumseismic.com for more information and to arrange a complimentary consultation.  Remember, what you don’t know can cost you a lot of money.

Ali Sahabi, a licensed General Engineering Contractor (GEC), is an expert in seismic resilience and sustainability. He is Co-Founder and Chief Operating Officer of Optimum Seismic, Inc., which has completed more than 3,500 seismic retrofitting and renovation projects for multifamily residential, commercial, and industrial buildings throughout California.  For more information visit www.optimumseismic.com.

[i] FEMA, Hazus Estimated Annual Earthquake Losses for the United States, P-366 Hazus Esimated Annual Earthquake Losses for the United States (fema.gov)

[ii] USGS,  The ShakeOut Earthquake Scenario - A Story That Southern Californians Are Writing

[iii] Intermap Technologies, Risks of Hazard, https://www.intermap.com/risks-of-hazard-blog/2015/05/2/how-vulnerable-is-your-building-to-earthquake-risk