From temblor- “Earthquake Early Warning: Gravity changes beat seismic signals”



November 30, 2017
Jean Paul Ampuero, Caltech Seismological Laboratory; Université Côte d’Azur, IRD, Géoazur

The devastating 2011 Tohoku earthquake and ensuing tsunami caused billions of dollars of damage and the deaths of thousands. A new study, using data from this quake, suggests that small gravity changes are the earliest earthquake early warning signals. Photo from: SFDEM

This story starts a few years ago, when astrophysicists in search for gravitational waves from the distant universe crossed paths with seismologists starving for new clues about how earthquakes work beneath our feet. Someone’s noise soon became someone else’s signal, indeed a very unique signal: the earliest harbinger of earthquake shaking that nature and physics have to offer.

Earthquakes move mass around, in enormous quantities. This is obvious to anyone who has been mesmerized by the view of fault offsets of several meters left at the Earth’s surface after a large earthquake. But mass is also redistributed temporarily by seismic waves, even before the earthquake is over. For example, P waves compress and dilate the rock they travel through, perturbing the rock’s density momentarily. These static and dynamic mass perturbations are natural sources of gravity changes … and gravity changes travel remotely at the speed of light!

Earthquake early warning (EEW), which aims at alerting people and automated systems seconds before strong shaking arrives, is one of the important contributions of modern seismology to society. But current EEW systems have a fundamental limitation: the natural information carrier they rely on, P waves, travels only about twice as fast as the natural damage carrier they try to anticipate, S waves. Just like lightning warns us of impending thunder, speed-of-light gravity changes are, in principle, the ultimately-fast earthquake information carrier.

Our team, a mix of physicists and seismologists in the US and Europe, used pen-and-paper and supercomputers to make a first theoretical estimation of how large these early gravity signals could be (Harms et al, 2015). The results looked “promising”: observing the phenomenon with current instrumentation promised to be a nice challenge. Our best bet was then to look for recordings of the huge 2011 Tohoku, Japan earthquake by a superconductive gravimeter installed in a quiet underground site, 500 km away from the epicenter, and by nearby broadband seismic stations. A blind statistical analysis of the data (of the type our gravitational-wave astrophysics colleagues are used to) revealed evidence of a signal preceding the P waves (Montagner et al, 2016). But it was not the smoking gun one would have hoped for. Moreover, my Caltech colleague Prof. Tom Heaton pointed out (Heaton, 2017) that our theory did not account for a potentially important feedback of gravity changes on elastic deformation, which I describe below.

The smoking gun and a more complete theory of early elasto-gravitational earthquake signals are finally reported in our paper published this week in Science Magazine (Vallée et al, 2017). We found that broadband seismometers in China located between 1,000 and 2,000 km away from the epicenter recorded, consistently and with high signal-to-noise ratio, an emergent signal that preceded the arrival of P waves from the Tohoku earthquake by more than one minute. These signals are well predicted by the results of a new simulation method we developed to account for the following physical process. The gravity perturbations induced directly by earthquakes (those studied by Harms et al, 2015) also act as distributed forces that deform the crust and produce ground acceleration. Gravimeters and seismometers are inertial sensors coupled to the ground, they actually record the difference between gravitational acceleration and ground acceleration. Sometimes these two accelerations are of comparable amplitude and tend to cancel each other, thus it is important to include both in simulations.

This figure, modified from IPGP, 2017, shows the signal picked up by a seismometer in the time preceding and following the 2011 M=9.1 Tohoku earthquake. What is important to see in this figure is that there is a 45-60 second window from when the prompt signal drops below normal background rates, until a P wave can be felt. This represents the potential earthquake early warning time. (Figure from Vallée et al., 2017)

How can we use these results to improve current EEW systems? Elasto-gravitational signals carry information about earthquake size but are weak and do not have a sharp onset. We had to use very distant seismic stations and wait more than one minute after the Tohoku mega-earthquake started to see its elasto-gravitational signals on conventional seismometers. This seems too long a wait for an EEW system, but it is enough to significantly accelerate current tsunami warning systems. Indeed our simulations show that the Chinese stations could distinguish earthquakes in Japan with Mw<8.5 from much larger ones within a few minutes (Vallée et al, 2017). This capability may be improved in the near future by exploiting modern array techniques to mitigate microseism noise. Who would have thought that a broadband seismic network in the Brazilian Amazon could someday help warn the megacity of Lima, Peru of an impending tsunami?

To develop the full potential of elasto-gravity signals for EEW (and, more fundamentally, for earthquake source studies) we need to develop new, more sensitive instruments. We can leverage on technological advances in gravity gradiometry for low-frequency gravitational wave (GW) detection. The GW detections that led to the recent Nobel Prize were achieved at frequencies of about 100 Hz and required huge facilities, but the GW astronomy community is also interested in observing GW signals in the 0.1-1 Hz band with much lighter and smaller (meter scale) instrumentation. The sensor requirements for EEW are much less stringent than those for GW detection, and should be achieved much sooner.

My personal affair with this new field of gravitational seismology started with a scholar chat at the Caltech Seismolab with Jan Harms, who was then a LIGO postdoc, and continued soon after with my old-time friends from IPG Paris. It has been wonderful to experience first-hand that EEW research is not only about operational and engineering aspects, but also about fundamental physics problems. I also find it exciting that the ongoing revolution of gravitational wave astronomy will not only open new windows into the distant Universe but also into our own vulnerable Earth.


J. Harms, J. P. Ampuero, M. Barsuglia, E. Chassande-Mottin, J.-P. Montagner, S. N. Somala and B. F. Whiting (2015), Transient gravity perturbations induced by earthquake rupture, Geophys. J. Int., 201 (3), 1416-1425, doi: 10.1093/gji/ggv090

T. H. Heaton (2017), Correspondence: Response of a gravimeter to an instantaneous step in gravity, Nature Comm., 8 (1), 966, doi: 10.1038/s41467-017-01348-z

J.-P. Montagner, K. Juhel, M. Barsuglia, J. P. Ampuero, E. Chassande-Mottin, J. Harms, B. Whiting, P. Bernard, E. Clévédé, P. Lognonné (2016), Prompt gravity signal induced by the 2011 Tohoku-oki earthquake, Nat. Comm., 7, 13349, doi: 10.1038/ncomms13349

M. Vallée, J. P. Ampuero, K. Juhel, P. Bernard, J.-P. Montagner, M. Barsuglia (December 1st 2017), Observations and modeling of the elastogravity signals preceding direct seismic waves, Science, doi: 10.1126/science.aao0746

See the full article here .

Please help promote STEM in your local schools.


Stem Education Coalition

You can help many citizen scientists in detecting earthquakes and getting the data to emergency services people in affected area.
QCN bloc

Quake-Catcher Network

The Quake-Catcher Network is a collaborative initiative for developing the world’s largest, low-cost strong-motion seismic network by utilizing sensors in and attached to internet-connected computers. With your help, the Quake-Catcher Network can provide better understanding of earthquakes, give early warning to schools, emergency response systems, and others. The Quake-Catcher Network also provides educational software designed to help teach about earthquakes and earthquake hazards.

After almost eight years at Stanford, and a year at CalTech, the QCN project is moving to the University of Southern California Dept. of Earth Sciences. QCN will be sponsored by the Incorporated Research Institutions for Seismology (IRIS) and the Southern California Earthquake Center (SCEC).

The Quake-Catcher Network is a distributed computing network that links volunteer hosted computers into a real-time motion sensing network. QCN is one of many scientific computing projects that runs on the world-renowned distributed computing platform Berkeley Open Infrastructure for Network Computing (BOINC).


BOINC WallPaper

The volunteer computers monitor vibrational sensors called MEMS accelerometers, and digitally transmit “triggers” to QCN’s servers whenever strong new motions are observed. QCN’s servers sift through these signals, and determine which ones represent earthquakes, and which ones represent cultural noise (like doors slamming, or trucks driving by).

There are two categories of sensors used by QCN: 1) internal mobile device sensors, and 2) external USB sensors.

Mobile Devices: MEMS sensors are often included in laptops, games, cell phones, and other electronic devices for hardware protection, navigation, and game control. When these devices are still and connected to QCN, QCN software monitors the internal accelerometer for strong new shaking. Unfortunately, these devices are rarely secured to the floor, so they may bounce around when a large earthquake occurs. While this is less than ideal for characterizing the regional ground shaking, many such sensors can still provide useful information about earthquake locations and magnitudes.

USB Sensors: MEMS sensors can be mounted to the floor and connected to a desktop computer via a USB cable. These sensors have several advantages over mobile device sensors. 1) By mounting them to the floor, they measure more reliable shaking than mobile devices. 2) These sensors typically have lower noise and better resolution of 3D motion. 3) Desktops are often left on and do not move. 4) The USB sensor is physically removed from the game, phone, or laptop, so human interaction with the device doesn’t reduce the sensors’ performance. 5) USB sensors can be aligned to North, so we know what direction the horizontal “X” and “Y” axes correspond to.

If you are a science teacher at a K-12 school, please apply for a free USB sensor and accompanying QCN software. QCN has been able to purchase sensors to donate to schools in need. If you are interested in donating to the program or requesting a sensor, click here.

BOINC is a leader in the field(s) of Distributed Computing, Grid Computing and Citizen Cyberscience.BOINC is more properly the Berkeley Open Infrastructure for Network Computing, developed at UC Berkeley.

Earthquake safety is a responsibility shared by billions worldwide. The Quake-Catcher Network (QCN) provides software so that individuals can join together to improve earthquake monitoring, earthquake awareness, and the science of earthquakes. The Quake-Catcher Network (QCN) links existing networked laptops and desktops in hopes to form the worlds largest strong-motion seismic network.

Below, the QCN Quake Catcher Network map
QCN Quake Catcher Network map

Earthquake country is beautiful and enticing

Almost everything we love about areas like the San Francisco bay area, the California Southland, Salt Lake City against the Wasatch range, Seattle on Puget Sound, and Portland, is brought to us by the faults. The faults have sculpted the ridges and valleys, and down-dropped the bays, and lifted the mountains which draw us to these western U.S. cities. So, we enjoy the fruits of the faults every day. That means we must learn to live with their occasional spoils: large but infrequent earthquakes. Becoming quake resilient is a small price to pay for living in such a great part of the world, and it is achievable at modest cost.

A personal solution to a global problem

Half of the world’s population lives near active faults, but most of us are unaware of this. You can learn if you are at risk and protect your home, land, and family.

Temblor enables everyone in the continental United States, and many parts of the world, to learn their seismic, landslide, tsunami, and flood hazard. We help you determine the best way to reduce the risk to your home with proactive solutions.

Earthquake maps, soil liquefaction, landslide zones, cost of earthquake damage

In our iPhone and Android and web app, Temblor estimates the likelihood of seismic shaking and home damage. We show how the damage and its costs can be decreased by buying or renting a seismically safe home or retrofitting an older home.

Please share Temblor with your friends and family to help them, and everyone, live well in earthquake country.

Temblor is free and ad-free, and is a 2017 recipient of a highly competitive Small Business Innovation Research (‘SBIR’) grant from the U.S. National Science Foundation.

ShakeAlert: Earthquake Early Warning

The U. S. Geological Survey (USGS) along with a coalition of State and university partners is developing and testing an earthquake early warning (EEW) system called ShakeAlert for the west coast of the United States. Long term funding must be secured before the system can begin sending general public notifications, however, some limited pilot projects are active and more are being developed. The USGS has set the goal of beginning limited public notifications by 2018.

The primary project partners include:

United States Geological Survey
California Governor’s Office of Emergency Services (CalOES)
California Geological Survey
California Institute of Technology
University of California Berkeley
University of Washington
University of Oregon
Gordon and Betty Moore Foundation

The Earthquake Threat

Earthquakes pose a national challenge because more than 143 million Americans live in areas of significant seismic risk across 39 states. Most of our Nation’s earthquake risk is concentrated on the West Coast of the United States. The Federal Emergency Management Agency (FEMA) has estimated the average annualized loss from earthquakes, nationwide, to be $5.3 billion, with 77 percent of that figure ($4.1 billion) coming from California, Washington, and Oregon, and 66 percent ($3.5 billion) from California alone. In the next 30 years, California has a 99.7 percent chance of a magnitude 6.7 or larger earthquake and the Pacific Northwest has a 10 percent chance of a magnitude 8 to 9 megathrust earthquake on the Cascadia subduction zone.

Part of the Solution

Today, the technology exists to detect earthquakes, so quickly, that an alert can reach some areas before strong shaking arrives. The purpose of the ShakeAlert system is to identify and characterize an earthquake a few seconds after it begins, calculate the likely intensity of ground shaking that will result, and deliver warnings to people and infrastructure in harm’s way. This can be done by detecting the first energy to radiate from an earthquake, the P-wave energy, which rarely causes damage. Using P-wave information, we first estimate the location and the magnitude of the earthquake. Then, the anticipated ground shaking across the region to be affected is estimated and a warning is provided to local populations. The method can provide warning before the S-wave arrives, bringing the strong shaking that usually causes most of the damage.

Studies of earthquake early warning methods in California have shown that the warning time would range from a few seconds to a few tens of seconds, depending on the distance to the epicenter of the earthquake. For very large events like those expected on the San Andreas fault zone or the Cascadia subduction zone the warning time could be much longer because the affected area is much larger. ShakeAlert can give enough time to slow and stop trains and taxiing planes, to prevent cars from entering bridges and tunnels, to move away from dangerous machines or chemicals in work environments and to take cover under a desk, or to automatically shut down and isolate industrial systems. Taking such actions before shaking starts can reduce damage and casualties during an earthquake. It can also prevent cascading failures in the aftermath of an event. For example, isolating utilities before shaking starts can reduce the number of fire initiations.

System Goal

The USGS will issue public warnings of potentially damaging earthquakes and provide warning parameter data to government agencies and private users on a region-by-region basis, as soon as the ShakeAlert system, its products, and its parametric data meet minimum quality and reliability standards in those geographic regions. The USGS has set the goal of beginning limited public notifications by 2018. Product availability will expand geographically via ANSS regional seismic networks, such that ShakeAlert products and warnings become available for all regions with dense seismic instrumentation.

Current Status

The West Coast ShakeAlert system is being developed by expanding and upgrading the infrastructure of regional seismic networks that are part of the Advanced National Seismic System (ANSS); the California Integrated Seismic Network (CISN) is made up of the Southern California Seismic Network, SCSN) and the Northern California Seismic System, NCSS and the Pacific Northwest Seismic Network (PNSN). This enables the USGS and ANSS to leverage their substantial investment in sensor networks, data telemetry systems, data processing centers, and software for earthquake monitoring activities residing in these network centers. The ShakeAlert system has been sending live alerts to “beta” test users in California since January of 2012 and in the Pacific Northwest since February of 2015.

In February of 2016 the USGS, along with its partners, rolled-out the next-generation ShakeAlert early warning test system in California. This “production prototype” has been designed for redundant, reliable operations. The system includes geographically distributed servers, and allows for automatic fail-over if connection is lost.

This next-generation system will not yet support public warnings but does allow selected early adopters to develop and deploy pilot implementations that take protective actions triggered by the ShakeAlert notifications in areas with sufficient sensor coverage.

The USGS will develop and operate the ShakeAlert system, and issue public notifications under collaborative authorities with FEMA, as part of the National Earthquake Hazard Reduction Program, as enacted by the Earthquake Hazards Reduction Act of 1977, 42 U.S.C. §§ 7704 SEC. 2.

For More Information

Robert de Groot, ShakeAlert National Coordinator for Communication, Education, and Outreach