From temblor: “Seismic warning to India: A shock strikes just north of Delhi”

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From temblor

February 25, 2019
By Aron Mirwald, M.Sc.
Ross Stein, Ph.D., Temblor, Inc.

On 20 February 2019, a magnitude 4 earthquake struck 50 km (30 mi) north from the megacity, Delhi. A magnitude 4 earthquake is not large. If it occurs nearby, it can be felt, and may generate some damage, but it is almost never fatal. This earthquake was no exception: shaking has been reported to be weak to moderate. So, what is interesting about it? Actually, there is a lot to be learned from small, seemingly unimportant events like this. Let us use this earthquake as a means to explore the seismic risk in India.

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This portion of a new map from the GEM Foundation shows the expected cost of earthquake damage relative to the cost of construction, averaged over time, everywhere on Earth. The Himalayan Foothill Thrust region lights up in a band of yellow-orange high risk. The risk is the product of a very high seismic hazard and an extremely high population density. Pakistan and Nepal are also seen to be at very high risk, followed by greater Kabul in Afghanistan.

Crushing into Eurasia

We know from GPS observations that the Indian plate is moving 16-18 millimeters per year towards the Eurasian plate (Bilham & Ambraseys, 2005). It is pushed, rather forcefully, below the Eurasian plate. This movement has resulted in the creation of the beautiful Himalayas. But it has also resulted in a thrust-zone, where many great earthquakes occur. In this zone, the two plates are interlocked most of the time. Since the plate is pushing from behind, the stress builds up until it is strong enough to overcome fault friction. Then, very large earthquakes can occur.

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India has been in a slow-motion crash into Asia for 40 million years, as attested to by 500 years of historical reports of great earthquakes, with events striking principally along India’s northern frontier. Some 400 million people live in the Ganges Plain (bright white area), just south of the frontier, in India and Bangladesh. Graphic by Volkan Sevilgen.

At the thrust-zone between the Indian and Eurasian plate, at least three earthquakes with a magnitude larger than 8 have occurred in medieval times (Bilham, 2009). The recurrence time of this kind of earthquakes is unknown, but it is speculated that earthquakes of similar magnitude are overdue (Bilham & Ambraseys, 2005).

But, if we take a closer look at last week’s earthquake, it did not occur at the thrust-zone, but further in the south. Actually, there are many earthquakes known to occur far away from the thrust-zone. This could be easily explained, if the Indian plate itself was deformed substantially. But, we know that the rate of deformation along the continent is very low, around 5 millimeters per year (Bilham, 2004). This is too low to explain frequent seismicity.

The Indian plate is buckling

The explanation is simple, yet fascinating. The downward bend of the Indian plate beneath the Himalayas has resulted in a ‘flexure’, or bending, of the plate. We can see this in the cross—section south of the thrust-zone. There is first an upward bulge of approximately 450 meters, followed by a smaller depression (Bilham, 2004). Now, we can imagine the plate to be like a wooden stick: it bends before it breaks.

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In this cross-section, North is to the right, and South to the left. The buckling of the Indian plate leads to a bulge south of Delhi, along with shallow tensional quakes, as struck last week. The great earthquakes strike along the thrust fault at right (purple), as well as other sites of concentrated buckling (Bilham, 2009).

The first part that breaks is usually a weak spot. In tectonic plates such weak spots are often faults, planes where the rock has failed previously due to an earthquake. Weak planes, that were previously stable, will be pushed towards the thrust-zone, and move through the bulge, where the change of flexural stresses can trigger failure and consequently earthquakes.

Seismic Risk in India

Now we can put the picture together: Seismic risk in India can be attributed to earthquakes at the thrust-zone below the Himalayas, and to seismicity within the continent due to flexural stresses.

Delhi, as an example of a vulnerable metropolis, has a history of being affected by both (Iyengar, 2000). There are around 20 seismically active faults in the vicinity of Delhi capable of generating earthquakes. The Mahendraghar–Dehradhun fault, for instance, could produce an earthquake of magnitude 7 (Iyengar & Gosh, 2004). One problem is, that the fast urbanization in Delhi is leading to a rising number of buildings that are helpless even in the face of moderate sized earthquakes (Mittal et. al., 2012).

India is one of the countries with the most earthquake-related deaths. Just in the past century, over 100.000 people have died due to earthquakes in the country (Bilham, 2009). This number is unlikely to decrease in the future: Its population is growing, and the consequential increase of fatalities is foreseeable (Bilham, 2009).

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India lies in the cluster of countries in the upper right, which have suffered the largest number of large earthquakes and fatalities since the turn of the 19thth century (Bilham, 2009)

Hope for the best, prepare for the worst

In their hazard assessment, Nath and Thingbaijam (2012) conclude that the Bureau of Indian Standards underestimates the seismic risk in India and recommend updating the National Building Code. But there is another problem. According to Bilham (2009), constructers often ignore existing building codes. Among the reasons he lists are ignorance of the seismic risk and the engineering solutions to it, people trying to save money, and corruption. He suggests that this could be solved by education. If everybody knew about the fatal consequences of not including earthquake resistant structures, it would occur less frequently.

Often, action is only taken after the disaster, but that is too late for many. So, this comparatively small earthquake near the megacity should be a reminder to put more effort to raise awareness of the earthquake risk.

References

Bilham, Roger. The seismic future of cities. Bulletin of Earthquake Engineering, 2009, 7. Jg., Nr. 4, S. 839.
Bilham, Roger, et al. Earthquakes in India and the Himalaya: tectonics, geodesy and history. Annals of GEOPHYSICS, 2004.
Bilham, Roger; AMBRASEYS, Nicholas. Apparent Himalayan slip deficit from the summation of seismic moments for Himalayan earthquakes, 1500–2000. Current science, 2005, S. 1658-1663.
GEM Global Seismic Risk Map (Silva et al., 2018), https://maps.openquake.org/map/global-seismic-risk-map/
Iyengar, R. N. Seismic status of Delhi megacity. Current Science, 2000, 78. Jg., Nr. 5, S. 568-574.
Iyengar, R. N.; GHOSH, Susanta. Microzonation of earthquake hazard in greater Delhi area. Current Science, 2004, 87. Jg., Nr. 9, S. 1193-1202.
Mittal, Himanshu, et al. Stochastic finite modeling of ground motion for March 5, 2012, Mw 4.6 earthquake and scenario greater magnitude earthquake in the proximity of Delhi. Natural Hazards, 2016, 82. Jg., Nr. 2, S. 1123-1146.
Nath, S. K.; Thingbaijam, K. K. S. Probabilistic seismic hazard assessment of India. Seismological Research Letters, 2012, 83. Jg., Nr. 1, S. 135-149.

See the full article here .


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Stem Education Coalition

Earthquake Alert

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Earthquake Alert

Earthquake Network project

Earthquake Network is a research project which aims at developing and maintaining a crowdsourced smartphone-based earthquake warning system at a global level. Smartphones made available by the population are used to detect the earthquake waves using the on-board accelerometers. When an earthquake is detected, an earthquake warning is issued in order to alert the population not yet reached by the damaging waves of the earthquake.

The project started on January 1, 2013 with the release of the homonymous Android application Earthquake Network. The author of the research project and developer of the smartphone application is Francesco Finazzi of the University of Bergamo, Italy.

Get the app in the Google Play store.

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Smartphone network spatial distribution (green and red dots) on December 4, 2015

Meet The Quake-Catcher Network

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).

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

ShakeAlert: An Earthquake Early Warning System for the West Coast of the United States
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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 in 2018.

Watch a video describing how ShakeAlert works in English or Spanish.

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. ShakeAlert can give enough time to slow 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 in 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” 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 joined by Oregon and Washington in April 2017. This West Coast-wide “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.

Authorities

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
rdegroot@usgs.gov
626-583-7225

Learn more about EEW Research

ShakeAlert Fact Sheet

ShakeAlert Implementation Plan