From temblor: “Sunda Strait tsunami launched by sudden collapse of Krakatau volcano into the sea”


From temblor

December 23, 2018
Jason Patton

Residents of the islands of Sumatra and Java were surprised by an unexpected tsunami yesterday. At the time we write this, there are reports of over 200 unfortunate deaths.

Cause: Earthquake, Landslide, or Volcanic Eruption?

Satellite imagery comparison based on Copernicus Sentinel-1 satellite imagery.

ESA/Sentinel 1

Tsunami can be triggered by 4 processes: earthquakes, landslides, weather causes (storms), and volcanic eruptions. Tide gages in the Sunda Strait recorded the tsunami and there is a wide range of observations that can be found on social media. Tsunami caused by submarine landslides can be nearly impossible to plan for and there is typically very little advance notice.

The Sunda Strait is the seaway that is formed between the islands of Java and Sumatra, Indonesia. This area of the world is best known for the 1883 eruption of Krakatau (or Krakatoa). This is a region of active tectonics and the deadly earthquake and tsunami from 2004 is still in our minds and hearts, not to mention the tsunami in Palu, Sulawesi, Indonesia just a short time ago.

After the tsunami hit, people immediately thought about the Anak Krakatau volcano as a possible source, where there has been ongoing eruptions for several years. This volcano is located where the 1883 eruption happened and is part of the same volcanic system. There are ongoing efforts to monitor this volcanic system (Hoffmann-Rothe, et al., 2006).

The vitally important service from national organizations like the European Union provide near real time satellite imagery. When compared with historic imagery, we have the ability to evaluate changes at the Earth’s surface.

The landslide could have itself been triggered by earthquakes or an eruption. Considering the low level of seismicity, the eruption is the likely culprit. Because the eruption is continuing, the possibility for additional landslides and tsunami should be considered for people who live along the coastline in the Sunda Strait.

We have outlined the general location of the shoreline on these images to take a first glance at the size of the landslide. The images are imperfect and this analysis is an approximation. The source of the satellite imagery is listed in the references below.

We have also outlined the spatial extent of the shoreline of Krakatau prior to the 1883 eruption.


The eruption in 1883 is known around the world because it had a global impact upon the climate for several years. Simon Winchester wrote a book entitled Krakatoa: The Day the World Exploded, August 27, 1883 and this is considered an excellent text that helps people learn about the eruption and the impact of volcanic hazards.

The 1883 eruption also caused a tsunami that caused devastation along the coastline and killed several thousand people. Below is a lithograph showing the 1883 eruption. This was published in 1888 (Royal Society, 1888).

An 1888 lithograph of the 1883 eruption of Krakatoa.

The Smithsonian Institution has an excellent website that covers the monitoring of volcanoes around the globe. Here is the webpage for the Anak Krakatau volcano.

There are lots of videos and photos of the ongoing eruptions. Below is a spectacular video taken from an airplane sent by the Indonesian Government to investigate the situation.

These natural hazards span the globe. Learn more about your exposure to natural hazards at

Tsunami Without Warning

The tsunami lasted about an hour in places and created both sea level rise and fall.

Below are two tide gage records from the region nearest the volcanic islands in the Sunda Strait. The upper panels show the tsunami records. The lower panel is a map showing the locations relative to Anak Krakatau.



Tide gage records from . Vertical scale is in meters (about the same size as a yard).

The tide gage record reveals that there was about 40 minutes from the first wave arrival to the highest and most destructive inundation. So, even without an expensive tsunami warning buoy system, or without a Krakatau Island seismic and GPS monitoring network, we can see, in retrospect, that warning was possible. A rate-of-change detector on tide gages could have been effective if a signal were sent to cell phones.

Out of the 2004 ‘Boxing Day’ M=9.2 earthquake tsunami catastrophe was born the DART buoy system in the Pacific and Indian Oceans. Out of the 2011 M=9.0 Tohoku earthquake tsunami disaster was born much faster and more accurate tsunami warnings when triggered by large offshore quakes.

Wouldn’t it be great if, out of this tragedy, a simple but effective warning system arose that could be ‘bolted on’ to existing telemetered tide gages that are already in place along the Pacific Ring of Fire and other volcanic centers?


Hoffmann-Rothe, A., Seht, M.I-V., Knieb, R., Faber, E., Klinge, K., Reichert, C., Purbawinata, M.A., and Patria, C., 2006. Monitoring Anak Krakatau Volcano in Indonesia in EOS Transactions, v. 87, no. 81, p. 581, 585-586

Royal Society, 1888. The Eruption of Krakatoa and Subsequent Phenomena, Report of the Krakatoa Committee of the Geological Society, London, Trubner and Co.

See the full article here .


Please help promote STEM in your local schools.

Stem Education Coalition

Earthquake Alert


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.

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

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.


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

Learn more about EEW Research

ShakeAlert Fact Sheet

ShakeAlert Implementation Plan