From temblor: “M=5.4 earthquake strikes the Philippines and shakes Manila”

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temblor

May 26, 2017
David Jacobson

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Manila, the capital city of the Philippines, experienced shaking in yesterday’s M=5.4 earthquake. (Photo from: angkulet.com)

Yesterday, at 10:27 p.m. local time, a M=5.4 earthquake struck the island of Luzon in the Philippines and was felt in the capital city of Manila, which is home to nearly 2 million people. On the USGS website, nearly 500 people reported feeling the quake, though we know many more actually felt it. According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), there are no reports of damage. Damage is also unlikely as the quake only caused light to moderate shaking. Despite the fact that the quake occurred at a depth of approximately 100 km, and was only a moderate magnitude, reports say that some people felt the quake for nearly 20 seconds in tall buildings.

The island of Luzon is the largest and most populated island in the Philippines, and is also very seismically active. To the west is the Manila trench, which is where the Sunda Plate subducts beneath the Philippine Sea Plate. To the east are both the East Luzon Trench and the Philippine Sea Trench, which are separated by a left-lateral transform boundary. The two subduction zones which bound the island mean that all of Luzon is susceptible to large earthquakes.

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This Temblor map shows the main faults around the Philippines. The island of Luzon is flanked to the west by the Manila Trench and to the east by the Philippine Sea Trench. Additionally, this map shows the Valley Fault System, which poses a great threat to the capital city of Manila. (Philippines faults from G-EVER)

Yesterday’s earthquake occurred at a depth suggesting it was on or near the western subducting slab. However, based on the USGS focal mechanism the quake had extensional and strike-slip motion rather than compressional. The strike-slip component can be explained by understanding that because of the subduction zones on either side of the island, the southern part of Luzon is being sheared. Furthermore, from the Temblor image above, one can also see that the southern portion of the Manila Trench begins trending to the southeast. This means that due to prevailing plate motion vectors, this part of the subduction zone is likely a transform or oblique boundary. The extensional component is a bit more tricky given the compressional regime that the Philippines sits in. However, when the dip of a subducting slab changes, tensional cracks can form and extensional faulting can result. Therefore, based on the depth of this quake, this is a likely explanation.

In addition to large subduction zones flanking the island of Luzon, there are also a series of surface faults, including the Valley Fault System, which runs straight through Manila. While this fault has not ruptured recently, 4 times in the past 1,400 years, it represents a great seismic hazard to Manila since it is capable of M=7+ earthquakes.

Based on the Global Earthquake Activity Rate (GEAR) model, we can see what types of earthquakes the island of Luzon could expect. This model uses global strain rates and seismicity since 1977 to forecast the likely earthquake magnitude in your lifetime anywhere on earth. In the Temblor map below, one can see that in the area around yesterday’s earthquake, the likely magnitude is 7.0+, while for Manila, it is 6.75+. Therefore, while yesterday’s quake should not be considered surprising, this map does give an indication that large earthquakes in the Philippines are possible, and likely.

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This Temblor map shows the Global Earthquake Activity Rate (GEAR) model for the Philippines. This model uses global strain rates and seismicity since 1977 to forecast the likely earthquake magnitude in your lifetime anywhere on earth. From this figure one can see that around the location of yesterday’s earthquake the likely magnitude is M=7.0, while around Manila it is M=6.75.

See the full article here .

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

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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