Phoning in earthquakes

At 3:20 a.m. on August 24, 2014 — not quite a year ago — a strong earthquake rockedthe northern California town of Napa. It sparked fires. Historic buildings crumbled. Andmore than 200 people were hurt. This region had not experienced ground shaking thatpowerful in nearly a quarter-century.

Less than one minute later, about 38 kilometers (24 miles) south of the Napa quake’sunderground origin, or epicenter, the quake’s waves reached the city of Berkeley. There,the waves swayed the apartment building where Qingkai Kong lay asleep.

Kong studies earthquake detection systems at the University of California, Berkeley. Forthis graduate student, the Napa quake was real — and a test. Bleary-eyed, Kongstumbled out of bed and glanced at an instrument on his desk. He saw the familiar flurryof jagged lines that signal an earthquake had occurred.

For many years, the only instruments that could provide that kind of information costthousands of dollars. This instrument was different: It was Kong’s Android smartphone.

Kong’s phone was running MyShake. This software application — or app — uses theinexpensive sensors in mobile devices to record ground movements. The squigglywaveforms of the Napa quake captured on his phone looked quite similar to thoserecorded by a nearby scientific sensor, Kong told Science News for Students.

Motion sensors in a smartphone recorded ground shakingduring the 2014 Napa earthquake. The phone detected motionin three dimensions — east/west, north/south and up/down.

As technological advances make smartphones ever smarter, researchers are enlistingthe owners of these popular devices to help study earthquakes. Similar projects are

placing portable sensors in homes, schools and offices.

Together, these citizen science projects are helping researchers create networks ofinstruments to measure earthquakes quickly and reliably. The efforts also are buildingawareness of the dangers that quakes pose and how to prepare for them. Eventually,these networks could underpin early-warning systems that can save lives.

In San Francisco, Calif., last December, Kong and others described some of thesecitizen networks. They also reported new data from these networks there at the fallmeeting of the American Geophysical Union, or AGU.

Earthquake basics

Earthquakes are common: Several million shake our planet each year. Recently,scientists have detected even more vibrations in areas where groundwater is pumped tothe surface or where carbon dioxide is injected belowground.

Most earthquakes are too small for people to feel. Such tiny quakes register less thanmagnitude 3.0. By comparison, the south Napa earthquake was a magnitude 6. Suchscores rate the intensity of ground motion triggered by a quake.

Parts of this building in downtown Napa, Calif., crumbled whena strong earthquake struck on August 24, 2014. One day,networked smartphones could help detect such quakes — andform part of an early-warning system.

Seismologists are scientists who study earthquakes. These experts measure groundmotion using seismographs. Such devices detect seismic waves, which are theenergetic waves traveling through Earth’s upper layers during a quake. The machinesthat record these waves are called seismographs. The U.S. Geological Survey (USGS)relies on very sensitive types of these devices. Each instrument is about the size of a

full-size fridge. The devices also cost $10,000 to $20,000 — plus another $50 per monthto operate.

Given their size and big price tag, quake mappers can’t plunk these seismographs justanywhere, explains Jennifer Strauss. She works at UC Berkeley’s SeismologicalLaboratory. There she helps connect its research to the needs of people andcompanies. Explains Strauss: “You can’t put one on a hillside where birds will run into itor disturb it. Or next to a highway where every truck going over a bump is going toregister a signal.” Scientists instead must choose carefully where they install theseinstruments.

Fortunately, seismic sensors are shrinking in size and cost. Since the sensors send dataover the Internet, operating costs are falling too.

As a result, researchers can afford to place more instruments in more places. Thesehigher-density networks can better pinpoint where earthquakes start. The devices alsocan warn of smaller tremors, called aftershocks, which often follow a major quake.

Crowd-sourced science

The blue box on the floor of this San Francisco area garage is aportable NetQuakes seismic sensor. The size of a car battery, it

runs on a home wifi network and captures data on an ordinary2 gigabyte flash drive.

Since 2009, USGS has invited volunteers to help expand its seismic network. Theagency’s scientists have placed about 500 low-cost, car-battery-sized seismographs inand near the places where people live, work and study. These little blue boxes detectground movements in earthquake-prone urban areas throughout the United States.Most have been placed in and around Seattle, Los Angeles and San Francisco.

These “NetQuakes” sensors are not as sensitive as the bigger professional instruments.Still, the low-cost devices can detect quakes of magnitude 1 or 2. (For each increase inmagnitude, an earthquake produces 10 times more ground motion. It also releasesabout 32 times more energy.)

And still smaller and cheaper quake sensors are becoming available. Some attach topersonal computers using a USB port. After a volunteer connects the box anddownloads a web application, the sensor is “ready to go,” explains Monica Kohler. Sheis an engineer at the California Institute of Technology in Pasadena. “It records shakingfrom that site and sends info continuously to us. And the box is very inexpensive: Itcosts $300.”

At the December AGU meeting, Kohler and her coworkers presented their latest effortsin building the Community Seismic Network. Since 2011, this team has placed low-costsensors at some 400 homes and offices in or near Los Angeles. These sensors can onlydetect quakes that are magnitude 3 or higher. That makes them less sensitive than eventhe USGS’s NetQuakes devices.

These earthquake sensors can plug into your home computerthrough a USB port. They can detect magnitude 3 and larger

earthquakes.

Community Seismic Network

Data from seismometers go into producing “shake maps.” Researchers analyze thesemaps to determine which areas experienced earthquake vibrations. The maps can showwhere the ground is shaking with an accuracy of 10 kilometers to 20 kilometers (6 milesto 12 miles). However, “if you want to detect shaking on a block-by-block scale, youneed more sensors placed more densely,” Kohler notes.

Because the newest seismic sensors are so cheap, they are allowing researchers toexpand the quake-mapping network. Potentially this network could include thousands— even tens of thousands — of stations, Kohler says.

Laptops and phones

Cheaper sensors can spawn denser networks of seismic instruments. One example isthe Quake-Catcher Network (QCN). It has recruited roughly 3,400 volunteers around theglobe.

Some volunteers host quake sensors that resemble the finger-sized USB flash drivescommonly used to store and transfer computer files. Others instead collect seismic datausing motion sensors called accelerometers. Most laptops, tablets and smartphones hitthe stores already loaded with these sensors.

(Story continues below image)

Computers, smartphones and laptops at homes and offices worldwide collect ground motion data for the Quake-

Catcher Network. Blue triangles represent machines providing data to the network. Red dots mark previouslydetected earthquakes.

As their name implies, accelerometers detect motion due to acceleration forces.Acceleration is the rate at which the speed or direction of something changes over time.In smartphones, it’s the accelerometer that senses when you rotate a phone — and thensignals the display to rotate its image to match.

The accelerometer in a mobile device is sensitive enough to detect a magnitude 3 to 3.5earthquake whose epicenter is a few kilometers (miles) away. The accelerometer in adesktop sensor can record quakes as small as magnitude 2.5. If people havedownloaded the QCN app, their devices will send a report to scientists of any groundmovement that the sensors in their phones or computers have picked up. Researcherscan then pool and analyze all of the data that these devices capture.

“With these additional sensors, we could potentially detect an earthquake morequickly,” says Elizabeth Cochran. She is a geophysicist at the USGS EarthquakeScience Center in Pasadena. “With more data, you can get faster and more reliableestimates of earthquake location and magnitude.”

Within towns and buildings

Alaska is an earthquake hotspot. There, Quake-Catcher sensors already have been putto the test. In 2014, these devices were installed at 24 schools in Anchorage, Alaska’slargest city. Their installation coincided with the 50th anniversary of the 1964 “GoodFriday earthquake.” This magnitude-9.2 whopper shook the ground for nearly 5minutes. It was the second-largest earthquake ever recorded.

In September 2014, a magnitude-6.2 quake struck 130 kilometers (81 miles) northwestof downtown Anchorage. “In some areas, there was just rattling,” recalls Kathryn Kurtz.“In others, things were falling off shelves.” Kurtz coordinates math and sciencecurriculum for the Anchorage schools fitted with the Quake-Catcher sensors. Several ofthese instruments detected the shaking.

Close-up of smartphones recording a laboratory-simulatedearthquake on a shake table.

The seismograph at the school closest to the epicenter “showed significant shaking,”Kurtz says. Curiously, though, sensors at some schools farther from the earthquake’sorigin recorded more shaking than did those at closer sites. That’s because “it matterswhat kind of ground you’re sitting on,” she explains. “We saw that with the 1964 quake,too.”

Buildings and other structures face a particular risk of damage if built on a type of clayformed by ancient glaciers. Known as quick clay, this sediment liquefies when theground shakes. On the other hand, buildings on bedrock hardly budge. “The cool thingabout the seismographs is they gave us a sense of where in town the quakes are feltmore,” Kurtz says.

In southern California, smaller earthquakes can cause fractures in high-rise buildings.Some of the cracks likely will be “too small to see with the naked eye,” Kohler notes.“Yet they’ve probably occurred in many buildings and left them in a weakened state.”

Kohler’s team at Caltech has installed sensors in about 10 high-rise buildings in the LosAngeles area. One building has sensors on each of its 52 floors. “It’s amazing thepictures we’re getting,” Kohler says. “We can see how the building moves on an hourlybasis.” By watching how buildings sway in the wind — or in response to an earthquake— the researchers can scout for signs that it may need strengthening. Such fixups arecalled retrofitting. And they can make buildings more quake-resistant.

Shimmy sim city

Luckily, destructive earthquakes are rare. Strong shaking only happens occasionally —and at times and in locations no one can predict. But that also makes it difficult for

earthquake researchers who need to test their sensors.

One solution is to use a “shake table.” Some are able to hold rooms or small buildings.Engineers program these machines to jiggle and jerk, mimicking the ground motionsthat occur during an earthquake. “You input seismic waves to simulate an earthquakeand put smartphones on the table to see what they record,” explains Kong.

Earthquake Shake Table Rocks …

SHAKE IT This roughly 3-minute clip shows a building on a“shake table” and how it responds to a simulated earthquake.Discovery News

Recently, a different team of researchers conducted an earthquake simulation. Thisexperiment put a virtual network of quake-sensing smartphones to the test. The resultssuggest that such a network could warn some people in San Francisco up to 3 secondsbefore they would encounter the effects of a magnitude-7 quake across the SanFrancisco Bay, about 28 kilometers (17 miles) to the east. Details appeared April 10 inthe journal Science Advances.

Early warnings

Earthquakes can’t be predicted. Still, early-warning systems can let people know aquake has begun. Depending on their distance from a quake’s epicenter, sensors inJapan and Mexico already can provide warnings to some people there seconds aheadof any shaking. That might not seem like much. Still, it can be enough time for people totake cover — or for automated equipment to take action. Elevators might automaticallystop at the nearest floor. Firehouse doors could swing open to allow trucks to exit.

These warnings are possible because digital communication moves at near the speed oflight. By contrast, seismic waves travel through the ground more slowly, at only thespeed of sound. It also helps that there’s a lag time between the arrival of an

earthquake’s primary waves (p-waves) and secondary waves (s-waves). P-waves arespeedier. They’re the first to signal an earthquake. But the follow-up s-waves arestronger. That means they’re also more destructive.

This map of the northern California coast shows concentriccircles radiating out from a “blind zone.” This is where aquake’s epicenter is too close to allow a warning. Numbers onradiating circles show how many seconds of warning a good-seismic network might provide more distant regions.

UC Berkeley Seismological Laboratory

“Early warning systems alert you to the impending arrival of s-waves,” notes Kohler.Within a few miles of the epicenter, you might get less than a second of warning. “Thefarther from the earthquake you are, the more warning time you get,” she explains.

The United States does not yet have an earthquake warning system in place. InDecember, Congress awarded $5 million to USGS for a West Coast earthquake early-warning system called ShakeAlert. Firefighters, police and other emergency responders,along with some private companies, have been testing the system since 2012. However,before it can be deployed further, the system needs more testing — and another $33million, USGS scientists say.

The West Coast ShakeAlert system is now undergoing testing with about 625 sensors.

Eventually, researchers hope to expand the system. They’ll add smartphones andinexpensive low-cost quake sensors to the costlier network of seismographs that willform the backbone of this early-warning system. Doing so should greatly expand thesystem’s reach. The San Francisco Bay Area alone has millions of smartphone users.Points out Strauss, “If we could harness people’s smartphones that they have with themevery day, all day, then we’d have a vast seismic network easily available.”

Power Words

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acceleration The rate at which the speed or direction of something changes over time.

accelerometer An instrument for measuring vibrations or a change in the rate ofmovement. These sensors typically can measure movement changes in all threedimensions (front-to-back, side-to-side and up-and-down).

aftershock One or more smaller earthquakes that often follow a major earthquake.

bedrock The thick, solid rock layer than underlies the soil and other broken, rockymaterials on Earth’s surface.

carbon dioxide A colorless, odorless gas produced by all animals when the oxygenthey inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also isreleased when organic matter (including fossil fuels like oil or gas) is burned. Carbondioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convertcarbon dioxide into oxygen during photosynthesis, the process they use to make theirown food.

concentric A series of circles or rings that have a common center point.

citizen science Scientific research in which the public — people of all ages andabilities — participate. The data that these citizen “scientists” collect helps to advanceresearch. Letting the public participate means that scientists can get data from manymore people and places than would be available if they were working alone.

clay Fine-grained particles of soil that stick together and can be molded when wet.When fired under intense heat, clay can become hard and brittle. That’s why it’s used tofashion pottery and bricks.

crowdsourcing A term coined in 2005 for the collection of data from a large

community of volunteers — often over the Internet. For instance, those volunteers maycollect information intentionally (such as data on cloud cover, the appearance of aparticular butterfly or a recording of the call of a certain bird), then send the data tosome researcher. Alternatively, an app downloaded on someone’s phone might collectlight, vibrations or some other information periodically — and automatically — and thenrelay it over the Internet to researchers.

curriculum (plural: curricula) The official classroom materials (often readings) usedto lead students through a course of study on a particular topic.

earthquake A sudden and sometimes violent shaking of the ground, sometimescausing great destruction, as a result of movements within Earth’s crust or of volcanicaction.

epicenter The underground location along a fault where an earthquake starts.

flash drive A type of small data-storage device (typically smaller than a pack ofchewing gum) that can receive or transmit digital data through a USB port.

force Some outside influence that can change the motion of a body, hold bodies closeto one another, or produce motion or stress in a stationary body.

glacier A slow-moving river of ice hundreds or thousands of meters deep. Glaciers arefound in mountain valleys and also form parts of ice sheets.

geophysics The study of matter and energy on Earth and how they interact.

global positioning system Best known by its acronym GPS, this system uses a deviceto calculate the position of individuals or things (in terms of latitude, longitude andelevation — or altitude) from any place on the ground or in the air. The device does thisby comparing how long it takes signals from different satellites to reach it.

graduate student Someone working toward an advanced degree — typically aMaster’s degree of PhD — by taking classes and performing research. This work is doneafter the student has already graduated from college (usually with a four-year degree).

groundwater Water that is held underground in the soil or in pores and crevices inrock.

liquefy (in geology) A term for the movement of soil particles during an earthquake thatkeeps them from holding firm and serving as a solid foundation for buildings, roads,

bridge footings and other structures.

magnitude (in geology) A number used to describe the relative size of an earthquake. Itruns from 1 to more than 8 and is calculated by the peak ground motion as recorded byseismographs. There are several magnitude scales. One of the more commonly usedones today is known as the moment magnitude. It’s based on the size of a fault (crackin Earth’s crust), how much the fault slips (moves) during a quake, and the energy forcethat was required to permit that movement. For each increase in magnitude, anearthquake produces 10 times more ground motion, and releases about 32 times moreenergy. For perspective, a magnitude 8 quake can release energy equivalent todetonating 6 million tons of TNT.

network A group of interconnected people or things.

seismic wave A wave in the ground produced by an earthquake or other means.

seismometer (also known as a seismograph) An instrument that detects andmeasures tremors (known as seismic waves) as they pass through Earth.

seismology The science concerned with earthquakes and related phenomena. Peoplewho work in this field are known as seismologists.

sensor A device that picks up information on physical or chemical conditions — suchas temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation —and stores or broadcasts that information. Scientists and engineers often rely onsensors to inform them of conditions that may change over time or that exist far fromwhere a researcher can measure them directly.

simulate To deceive in some way by imitating the form or function of something. Asimulated dietary fat, for instance, may deceive the mouth that it has tasted a real fatbecause it has the same feel on the tongue — without having any calories. A simulatedsense of touch may fool the brain into thinking a finger has touched something eventhough a hand may no longer exists and has been replaced by a synthetic limb. (incomputing) To try and imitate the conditions, functions or appearance of something.Computer programs that do this are referred to as simulations.

smartphone A cell (or mobile) phone that can perform a host of functions, includingsearch for information on the Internet.

software The mathematical instructions that direct a computer’s hardware, including itsprocessor, to perform certain operations.

universal serial bus (abbreviated USB) A type of hardware technology used to connectsome peripheral device — such as a mouse, keyboard or thumb drive — to a computer,smartphone, digital camera or other electronic system.

urban Of or related to cities, especially densely populated ones or regions where lotsof traffic and industrial activity occurs. The development or buildup of urban areas is aphenomenon known as urbanization.

USB port The opening on a computer or other digital device into which a USBconnector can be inserted.

U.S. Geological Survey, or USGS This is the largest nonmilitary U.S. agency chargedwith mapping water, Earth and biological resources. It collects information to helpmonitor the health of ecosystems, natural resources and natural hazards. It also studiesthe impacts of climate and land-use changes. A part of the U.S. Department of theInterior, USGS is headquartered in Reston, Va.

vibrate To rhythmically shake or to move continuously and rapidly back and forth.

virtual Being almost like something. An object or concept that is virtually real would bealmost true or real — but not quite. The term often is used to refer to something that hasbeen modeled — by or accomplished by — a computer using numbers, not by usingreal-world parts. So a virtual motor would be one that could be seen on a computerscreen and tested by computer programming (but it wouldn’t be a three-dimensionaldevice made from metal).

wave A disturbance or variation that travels through space and matter in a regular,oscillating fashion.

wifi (also Wi-Fi) A wireless technology that networks various electronic devices (suchas cell phones and laptop computers); it allows them to share the same modem forInternet connections by using radio waves.

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