Trembling Truckee Meadows: Understanding Reno’s Earthquakes
If you’ve lived in the Reno area for some time, chances are you’ve felt at least one earthquake. In fact, on Friday (October 27th), a Magnitude 4.5 earthquake struck near Topaz Lake and was felt throughout Carson City, Minden, and Gardnerville. Between October 18th and October 20th, just a few weeks ago, several earthquakes occurred near Spanish Springs- the largest registering a 3.5 on the Moment Magnitude Scale. Although these tremors were detectable by people and pets, they pale in comparison to the size of earthquake that could theoretically hit Reno (a Magnitude 7.5). In this article, we will learn what earthquakes are, why they occur, why they occur in Reno (and Nevada in general), and what you can do to make sure you’re safe during an earthquake.
What Is an Earthquake?
An earthquake is generally defined as the shaking of the Earth’s surface in response to a sudden release of energy in the Earth’s crust. Earthquakes occur on faults- planar fractures or discontinuities between two blocks of rock where there has been displacement due to rock mass movement. When an earthquake occurs, terms such as hypocenter, epicenter, and magnitude are often thrown around. The hypocenter, or focus, of an earthquake is the point inside the Earth where an earthquake occurs. The epicenter is the geographic location directly above the hypocenter. Simply put, an earthquake’s magnitude is the size of the earthquake on a logarithmic scale that measures its strength. A common misconception is that earthquake magnitude is measured on the Richter Scale, but in reality it is measured on the Moment Magnitude Scale. Earthquake magnitude is logarithmic- a magnitude 6.0 is 31.622 times more powerful than a 5.0, and a 7.0 is ~1000x more powerful than a 5.0. To further add perspective, a Magnitude 9.0 earthquake is roughly 1 MILLION times more powerful than a 5.0.
Why Do Earthquakes Occur?
Earthquakes occur, rudimentarily, because the Earth is always moving. The Earth has three main layers- the solid core, the molten mantle, and the solid crust. The crust is the top-most layer that we live on. It’s not one continuous solid entity floating atop the mantle- it’s “cut up” and composed of several slabs of solid rock that continuously move around, interacting with one another. These massive slabs of rock are tectonic plates, and the vast majority of earthquakes occur at/near tectonic plate boundaries or within weak areas of a tectonic plate. Tectonic plate movement is propelled by convection in the molten part of the Earth (mantle). Convection in geology is the phenomenon of heat transfer through the mantle from the core to the crust (naturally, heat rises- the core is VERY hot, the crust, not so much). Roughly 50% of the source of the heat within the Earth that generates convection is the radioactive decay of certain metals that naturally occur within the Earth: Uranium-238, Uranium-235, Thorium-232, and Potassium-40, among other radioactive isotopes. The other 50% of Earth’s heat is derived from residual primordial heat from its initial formation, roughly 4.54 billion years ago. This heat transfer creates currents in the mantle like currents in the ocean. Tectonic plates are basically continent-sized “boats” of solid rock that float atop the “ocean” of molten rock. They cover every square inch of the Earth, and constantly interact with other plates due to the underlying currents in the mantle.
Though tectonic plates are always moving, motion is not always seamless. Tectonic plates often get stuck on each other, as the Earth’s crust is solid and brittle. The molten mantle continues to constantly move, while the solid crust gets stuck on other masses of solid crust. When these plates get stuck on each other, they build tension, stress, and strain as the molten/ductile part of these plates (underneath the crust) continue to move. This stress not only builds up on the plate boundary, but also in areas near it, forming several fault lines that parallel plate boundaries. When the tension, stress, and strain has reached a critical point, the fault suddenly slips, and an earthquake occurs as the crust rapidly moves to re-equilibrate with the constantly moving mantle. It then gets stuck again, builds up more stress, and eventually another earthquake occurs, completing the cycle. This cycle continues due to the solid and brittle nature of the crust- it’s always getting stuck and cannot fluidly flow like the molten mantle beneath it. The recurrence interval for an earthquake depends on how fast the mantle is moving at the plate boundary or fault- where motion is relatively slow, recurrence interval can be as long as hundreds to thousands of years, while major earthquakes can occur on average every few years in areas where the plates are moving rapidly.
Why Are There Earthquakes in Reno?
The western United States is quite seismically active, due in part to the fact that the west coast lies on two different plate boundaries. In California, the San Andreas Fault marks the boundary between the North American and Pacific Plates. Here, the two plates slide past each other. In the Pacific Northwest, from northern California through Oregon, Washington, and up into Canada, the Cascadia Subduction Zone marks the boundary between the North American Plate and the Juan De Fuca Plate. Here, the Juan De Fuca Plate subducts (dives) under the North American Plate, creating structures such as the Cascade Range, Cascade volcanoes, and Washington’s Olympic Peninsula.
At the San Andreas Fault, the two plates slide past one another because the general movement of the Pacific Plate is northwest, while the general movement of the North American Plate is south-southwest. Meanwhile, the Juan De Fuca Plate’s general movement is due east, into North America. The Juan De Fuca Plate is denser than the North American Plate- thus diving beneath it. Both the San Andreas Fault and Cascadia Subduction Zone are active faults- capable of Magnitude 8.3 and Magnitude 9.4 earthquakes, respectively. These faults pose serious seismic risk for major cities including Los Angeles, San Francisco, Portland, and Seattle. Though the earthquake risk in these areas is high, Reno is safe, right? There aren’t any major faults running near or through Reno, right?
Actually, there are. Reno is situated in two seismically active geologic regions of North America- the Basin & Range and Walker Lane.
As aforementioned, earthquakes occur on plate boundaries and in weak areas within a tectonic plate, and the Basin and Range (also known as the Great Basin) is the latter. For the last 30 million years, the area between the Sierra Nevada and Rocky Mountains has been ripped apart, and continues to be torn asunder today. All of this pulling apart has caused crustal extension- making the crust thinner, but more stretched out between the Sierras and Rockies. Additionally, the molten mantle is much closer to the surface of the Earth here, as the crust weakens. The way that this manifests itself in terms of structural geology is the formation of horst and graben- fancy geologic words for long, linear mountain ranges and valleys, respectively.
In the Great Basin, long, skinny mountain ranges parallel to the direction of crustal extension are uplifted, while deep valleys are down-dropped in between them. Active faults bound the margins of these ranges and valleys. The faults are often long and linear- capable of earthquakes as strong as Magnitude 7. In fact, the largest earthquake that ever occurred in Nevada was on one of these faults- the 1954 Fairview earthquake near Fallon registered a 7.3 on the Moment Magnitude Scale. Reno is situated on the western edge of the Great Basin, and several active faults, including the Mount Rose Fault, Spanish Springs Valley Fault, Peavine Peak Fault, Little Valley Fault, Carson Range-Kings Canyon Fault, Petersen Mountain Fault, and Freds Mountain Fault run through the area and are associated with Basin and Range crustal extension. The recent earthquake that struck Topaz Lake (Oct 27, M. 4.5) was associated with this geological environment.
The second tectonically active area that Reno is situated in is a seismic belt known as Walker Lane. As aforementioned, the San Andreas Fault runs through California and acts as the border between the Pacific and North American Plates. With that being said, the boundary between the two plates is currently shifting eastward, in a trough immediately east of the Sierra Nevada, known as Walker Lane. Currently, the San Andreas Fault accounts for roughly 75% of the tectonic movement between the two aforementioned plates. Walker Lane accounts for the other 25%. Beginning in southeastern California near Lancaster, Walker Lane (known as the Eastern California Shear Zone in SE Cali) is not just one fault- it’s a series of faults that run from the Garlock Fault (near Lancaster) north through eastern California and Nevada to about Susanville. Reno is in the heart of Walker Lane, and within 7-8 million years, the border between the Pacific and North American plates will run right through the heart of Reno.
Several large earthquakes have occurred in Walker Lane recently, including the 2020 Magnitude 6.5 Monte Cristo Range earthquake near Tonopah (NV), the 2019 Ridgecrest earthquakes (6.4 and 7.1, CA), the 1999 Hector Mine earthquake (7.1, CA), the 1992 Landers earthquake (7.2, CA), the 1932 Cedar Mountain earthquake (7.2, NV), and the massive 1872 Lone Pine earthquake (7.9, CA). Large earthquakes will continue to occur on Walker Lane for millions of years to come. The Pyramid Lake Fault, Olinghouse Fault, Spanish Springs Peak Fault, Warm Springs Valley Fault, Dog Valley Fault, Honey Lake Fault, and Mohawk Valley Fault are just a few faults associated with Walker Lane that run through the Truckee Meadows and vicinity. The recent swarm of earthquakes near Spanish Springs (Oct 18-20), occurred on the Spanish Springs Peak Fault and were associated with tectonic movement from Walker Lane.
Reno has experienced several large earthquakes in the past, including the 1857 Truckee earthquake (6.0), the 1860 Reno earthquake (6.5), the 1868 and 1869 Virginia City earthquakes (6.0, 6.4), the 1887 Carson City earthquake (6.5), the 1914 Reno earthquake (6.4), and most recently, the 2008 Reno earthquake (5.1). According to the Nevada Bureau of Mines and Geology, the likelihood of an earthquake of Magnitude 6.5 or greater to strike the Truckee Meadows within the next 50 years is 50-60%. The Pyramid Lake Fault poses the largest seismic threat to Reno- it’s capable of producing a Magnitude 7.5 earthquake.
How To Stay Safe in an Earthquake
As you’ve now learned, Reno is susceptible to earthquakes and has had its fair share of tremors. Knowing that a large earthquake is more likely than not to occur within the next 50 years here, what can you do to stay safe during a large earthquake?
Though we cannot control or predict earthquakes, there are three major things that we as humans can control regarding earthquakes. These include engineering, preparation, and reaction.
The fact that Reno has experienced several large earthquakes in the recent past is actually a blessing for us today- because people remember large earthquakes that have occurred here, engineers have built all of Reno’s buildings to strict seismic codes. As such, the likelihood that your house will collapse, even in a very large earthquake here, is slim to none, even in older houses.
In terms of preparation, stockpiling a “bug out kit” is a great idea. In the event of a large earthquake, water, gas, and electricity lines could be severed, and having food, water, warmth, and entertainment is essential. Maybe go to Costco and buy some extra canned food that won’t go bad for a while, get some extra water, stockpile some blankets and warm clothes, procure flashlights and extra batteries, some cooking equipment, and a method to start a fire. Maybe include some playing cards or a board game to keep yourself entertained in the aftermath of a large quake. It’s best to have enough supplies for roughly two weeks stockpiled in your bug-out kit. Another aspect of preparation is devising a plan to rendezvous with loved ones and executing said plan in the event of an earthquake occurring while you are separated from your loved ones (i.e., at work or school). Most casualties from earthquakes actually occur after the shaking has stopped, due to people not having enough food, water, and supplies. As such, proper preparation is paramount and could save your life.
Lastly, your reaction and what you do during the shaking is critical. Avoid windows, door frames, and areas with precariously-hanging objects. When the shaking begins, protect your head and immediately go underneath a sturdy structure, such as a desk, table, or bed. Avoid panic and hysteria and if you’re in a building, DO NOT try to run out of it. This could severely injure you, and the buildings in the Truckee Meadows aren’t likely to collapse anyways, due to the strict seismic code they’ve been built to. Remain calm during the ordeal and hang onto the desk or table that you’ve crouched under. Wait it out. Once the shaking has stopped, remain wary for aftershocks, and execute your bug-out plan.
I hope you’ve learned all about earthquakes and how to survive one, as we are in Earthquake Country. Though we cannot control them, we can learn all about them and how to survive them. It all starts with education, and I strongly hope that this article has been educational and interesting.
References
Quakefeed app
About the Author
Solomon is an Interpretive Trail Guide here at Truckee Meadows Parks Foundation. Hailing from Las Vegas, Solomon has a B.S. in Geology from UNLV’s Honors College. Though he's lived most of his life in Las Vegas, he's also lived in New Mexico, Ohio, Hawaii, Elko, and Seattle. After receiving his degree in 2021, he spent time working in both the mining and civil engineering fields, but his undying passion for nature, education, and preserving the environment has brought him here to TMPF. In his free time, Solomon enjoys photography, researching and exploring the natural world, playing basketball, watching football, listening to and playing music, traveling, hanging out with friends and family, and making videos for his youtube channel.
