seismology

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Tōhoku Japanese Earthquake Sculpture by Luke Jerram

About the piece:

This sculpture was made to contemplate the 2011 Tōhoku earthquake and tsunami in Japan. To create the sculpture a seismogram of the earthquake, was rotated using computer aided design and then printed in 3 dimensions using rapid prototyping technology. The artwork measures 30cm x 20cm and represents 9 minutes of the earthquake.

Look for it soon at the Jerwood Space in London for a show called Terra. The show will also include his fantastic virus sculptures.

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Thingvellir National Park in Iceland is where the Vikings held their parliament meetings and the subsequent Icelandic government continued to use the sight to convene their general assembly from 930 to 1798. It’s also where the Eurasian and North-American tectonic plates meet, hence the huge fissure which is the result of earthquakes and seismic movement.

Happy Birthday Inge Lehmann, Discoverer of Earth's Inner Core

In 1929 a large earthquake occurred near New Zealand. Danish seismologist Inge Lehmann “the only Danish seismologist,” as she once referred to herself—studied the shock waves and was puzzled by what she saw. A few P-waves, which should have been deflected by the core, were in fact recorded at seismic stations. 

Lehmann theorized that these waves had traveled some distance into the core and then bounced off some kind of boundary. Her interpretation of this data was the foundation of a 1936 paper in which she theorized that Earth’s center consisted of two parts: a solid inner core surrounded by a liquid outer core, separated by what has come to be called the Lehmann Discontinuity. Lehmann’s hypothesis was confirmed in 1970 when more sensitive seismographs detected waves deflecting off this solid core.

Born in Denmark in 1888, Lehmann was a pioneer among women and scientists. Her early education was at a progressive school where boys and girls were treated exactly alike. This was a sharp contrast to the mathematical and scientific community she later encountered, about which she once protested to her nephew, Niles Groes, “You should know how many incompetent men I had to compete with—in vain.” Groes recalls, “I remember Inge one Sunday in her beloved garden…with a big table filled with cardboard oatmeal boxes. In the boxes were cardboard cards with information on earthquakes…all over the world. This was before computer processing was available, but the system was the same. With her cardboard cards and her oatmeal boxes, Inge registered the velocity of propagation of the earthquakes to all parts of the globe. By means of this information, she deduced new theories of the inner parts of the Earth.”

A critical and independent thinker, Lehmann subsequently established herself as an authority on the structure of the upper mantle. She conducted extensive research in other countries, benefiting from an increased global interest in seismology for the surveillance of clandestine nuclear explosions. When Lehmann received the William Bowie medal in 1971, the highest honor of the American Geophysical Union, she was described as “the master of a black art for which no amount of computerizing is likely to be a complete substitute.” Lehmann lived to be 105.

Learn more about Lehmann and experience the power of earthquakes in the exhibition Nature’s Fury: The Science of Natural Disasters, now on view. 

Inge Lehmann [1888 - 1993]

Inge Lehmann was a Danish Seismologist who discovered the Earth’s inner core. In 1936 she postulated from existing seismic data that the Earth’s core is not a single molten sphere, but that an inner core exists, which has physical properties that are different from those in the outer core. This conclusion was quickly accepted by seismologists, who up to this time had not been able to propose a workable hypothesis for the observation that the P-wave created by earthquakes slowed down when it reached certain areas of the inner Earth.

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The Most Dangerous City in the World

On the eastern edge of the Democratic Republic of Congo, the perilous Nyiragongo volcano towers 3470m over the city of Goma. The wildly erratic volcano is one of the most active on the planet, famous for the violent 200-metre-wide lava lake cradled in its vast summit crater, constantly emitting deadly gases and huge geysers of liquid rock. In 1977 and 2002, the volcano spewed deadly molten rock towards the million inhabitants of Goma, killing hundreds, forcing evacuations and destroying homes—but these were just small disturbances compared to what Nyiragongo is capable of unleashing. The volcano has an intricate ‘plumbing’ system like roots of a tree snaking deep underground, with vents not just at its summit but all around it, and so the threat to Goma is very immediate, and it has been dubbed ‘the most dangerous city in the world’ by researchers. The question is not if the volcano will erupt, but when. And yet, Nyiragongo is one of the least studied volcanoes in the world, because for the past twenty years, the Democratic Republic of Congo has experienced almost constant warfare. A deeper understanding of Nyiragongo must be gained in order to prevent a catastrophe, but serious research has only begun in the past few years. Until we can predict its activity, the question of when? will haunt scientists and seismologists alike, and will determine the fate of nearly one million people.

(Image Credit: Carsten Peter)

UC Berkeley’s Early Warning System Beat Napa Earthquake by 10 Seconds

Ten seconds before the San Francisco Bay Area started shaking early Sunday morning, an experimental system in a UC Berkeley lab sounded an alarm, counting down to the impending earthquake. The system works through an array of sensors near the fault line which calculate the severity of the quake and broadcast a warning.

It might not seem like much, but even a few seconds notice could allow utilities to shut off gas lines, elevators to let people off at the next floor, and trains to slow down. The USGS cites the benefits a warning could give to a doctor in the middle of performing surgery. In 2012, BART adopted an automatic braking system linked to the program, called Shake Alert.

Read more about UC Berkeley’s earthquake early warning system.

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MAJOR EARTHQUAKE TODAY

(CNN) – An 8.2-magnitude earthquake struck off the coast of northern Chile on Tuesday, generating a tsunami, authorities said.

The U.S. Geological Survey reported the quake, which hit at at 6:46 p.m. local time, was centered some 60 miles northwest of Iquique at a depth of 12.5 miles.

Chile’s National Emergency Office tweeted Tuesday night that it was asking everyone to evacuate the South American nation’s coast.  

A tsunami warning was in effect for Chile, Peru and Ecuador.

A tsunami watch was issued for Colombia, Panama and Costa Rica, according to the Pacific Tsunami Warning Center.

USGS National Earthquake Information Center

The April 1, 2014 M 8.2 earthquake in northern Chile occurred as the result of thrust faulting at shallow depths near the Chilean coast.

The location and mechanism of the earthquake are consistent with slip on the primary plate boundary interface, or megathrust, between the Nazca and South America plates. At the latitude of the earthquake, the Nazca plate subducts eastward beneath the South America plate at a rate of 65 mm/yr.

Subduction along the Peru-Chile Trench to the west of Chile has led to uplift of the Andes mountain range and has produced some of the largest earthquakes in the world, including the 2010 M 8.8 Maule earthquake in central Chile, and the largest earthquake on record, the 1960 M 9.5 earthquake in southern Chile.

NOAA Pacific Tsunami Warning Center

TSUNAMI INFORMATION STATEMENT NUMBER   3
NWS PACIFIC TSUNAMI WARNING CENTER EWA BEACH HI
235 PM HST TUE APR 01 2014

TO - CIVIL DEFENSE IN THE STATE OF HAWAII
SUBJECT - TSUNAMI INFORMATION STATEMENT

THIS STATEMENT IS FOR INFORMATION ONLY.
NO ACTION IS REQUIRED AT THIS TIME. HOWEVER… THE TSUNAMI THREAT TO HAWAII IS STILL BEING EVALUATED.

THE PACIFIC TSUNAMI WARNING CENTER HAS ISSUED AN EXPANDING REGIONAL TSUNAMI WARNING AND WATCH FOR PARTS OF THE PACIFIC  LOCATED CLOSER TO THE EARTHQUAKE. AN EVALUATION OF THE PACIFIC WIDE TSUNAMI THREAT IS UNDERWAY AND THERE IS A POSSIBILITY THAT HAWAII COULD BE ELEVATED TO A WATCH OR WARNING STATUS.

 IF TSUNAMI WAVES IMPACT HAWAII THEIR ESTIMATED EARLIEST ARRIVAL TIME IS   0324 AM HST WED 02 APR 2014

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With little warning Chile’s Calbuco volcano erupted with ferocity after 42 years of stability.

On April 22nd, plumes of ash began spewing from the volcano up to 10 kilometres in the air, and resulted in a large evacuation process as well as these powerful images. 

With warning of as little as 15 minutes for some residents, this eruption highlights the immense difficulty in forecasting volcanic eruptions. Chile has 400 or so active volcanoes - one of the highest amounts on the planet, yet there’s still little that can be done to efficiently predict these eruptions. 

The proximity of high population density near large volcanoes seen in countries like Chile, Malaysia and The US have experts in the field concerned about the measures taken to ensure safety. Volcanoes that have been dormant for hundreds or thousands of years can still spring to life, begging the question; what can we do to ensure safety of these populations?

(Nat Geo, Vox, Time)

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TSUNAMI ANIMATION: NORTHERN CHLE, 1 APRIL 2014

  • PTWC’s near real-time animation for the tsunami from northern Chile on 1 April 2014 resulting from an offshore 8.2 magnitude earthquake in the region. The animation shows simulated tsunami wave propagation for 30 hours followed by an “energy map” showing the maximum open-ocean wave heights over that period and the forecasted tsunami run up heights on the coastlines.
  • Animación en tiempo casi real del PTWC para el tsunami en el norte de Chile el 01 de abril 2014 como resultado de un terremoto en alta mar 8.2 de magnitud en la región. La animación muestra la propagación de ondas de tsunami simulado durante 30 horas, seguido de un “mapa de la energía” que muestra las alturas máximas de olas de mar abierto durante ese período y la altura prevista de impacto en la costas del océano pacifico.

When tectonic plates collide, sometimes one plate sinks, or subducts, below another one. This can trigger an earthquake. When earthquakes cause the ocean floor to move, the water moves, too. Columns of water travel across the ocean and grow taller as they approach land, becoming a tsunami.

Scientists use computer models to predict whether a tsunami will occur. The model can forecast the wave’s speed, direction, and height as it approaches land. Local authorities can then warn communities that might be in danger.

Learn more about earthquakes and tsunamis.

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Don’t be shaken – Lucy’s not leaving us

Even as the dust was still settling with our nerves still quaking, for many of us in Los Angeles, one woman seemed to have all the answers. That was Lucy Jones, the doctor on-call when the earthquakes strike. 

Some have called her the Beyoncé of earthquakes. Well, she just announced she’s retiring from the U.S. Geological Survey. (But don’t panic. She’s not leaving California behind.)

There’s been a lot of love for Lucy on Twitter. One response I got asked the question many of us have: “Who else will come out in her bathrobe in the middle of the night to say it probably was not a precursor?”

As reporter Rosanna Xia put it: In her 33 years with the USGS, Jones has become a universal mother for rattled Southern Californians. After each quake, she turns fear of the unknown into something understandable.

While most of the earthquake guys aren’t remembered, Dr. Jones is certainly unforgettable to many of us who grew up in Southern California. In addition to making something complicated understandable (and a little less scary), she also helped to dramatically change the way we prepare for earthquakes across Southern California. 


“When the big one hits, people will be living because of the work that she has done." 

– Los Angeles Mayor Eric Garcetti  


What’s next for her? Helping to develop science-based policies on climate change. 

What’s next for us? Wondering who will be the one to settle our nerves with information when we are still quaking after the inevitable next temblor.  


You can read more about Dr. Lucy Jones and her work here. 

@mmaltaisla 


Photos by Los Angeles Times

Seeing with Seismic Waves

Earth is a rocky terrestrial planet, layered like a spherical, incredibly hot, completely unpalatable cake (so, not really like a cake at all). The outermost layer is the crust, followed by the molten mantle, then the metallic core, which is made mainly of iron and nickel but split into two parts: the outer core is churning liquid, and the inner core is a dense, rotating solid ball.

The deeper we go down, the hotter and more pressurised it becomes. The deepest hole humans have every drilled is only 12 kilometres down, not even deep enough to hit the mantle. So how do we know the structure and composition of the planet?

Our knowledge mainly comes from seismology, which allows us to study the planet’s interior based on how seismic waves travel through it. Seismic waves are produced by earthquakes, and they cause rock to either compress or to vibrate up and down. There are two types: P and S waves.

  1. P waves cause matter to move in a horizontal motion, compressing and stretching it like a spring. Sound waves are P waves, compressing and stretching the air in order to travel. These types of waves are much faster than S waves, and can travel through both solids and liquids.
  2. S waves cause matter to move up and down or side to wide, like the waves that travel up and down a jolted rope. They cause the most damage when earthquakes occur, as they physically displace the earth much more violently, even though they’re slower than P waves. However, they can’t travel through liquids.

(Image Credit)

The speed, size, and direction of these waves change depending on the density, composition, and temperature of the material they pass through. The fact that S waves can’t travel through liquid, for example, is vital to our knowledge of Earth’s interior. When an earthquake occurs in the crust, S and P waves are not only felt on the surface, but they also shoot down right through the Earth and can be detected on other parts of the planet. When seismologists measure these earthquake signatures around the world, they see a “shadow zones” where no waves have made it through. The key to this lies in the abrupt differences between the layers of the Earth.

Since S waves cannot travel through liquid, they can’t pass from the mantle and into the liquid outer core. Instead, they reflect off at an angle, leaving a huge shadow zone on the opposite side of the earth.  Meanwhile, P waves (which can travel through liquid) are able to pass through the core and emerge on the other side. Because of the way they bend as they pass through different mediums (from the dense core to the less dense mantle), they also create two, smaller shadow zones.

(Image Credit)

From this information about how waves reflect and refract, we’ve deduced the four main layers of our planet.

The cool thing is, these principles aren’t limited to the study of Earth’s interior. Similar instruments can be used on the surface of any solid planet—Apollo astronauts actually left seismometers on the Moon. The Moon isn’t broken into plates like the Earth, which collide and slip to cause earthquakes, so moonquakes are instead caused by tidal deformation. The Viking 2 lander attempted to use a seismometer on Mars, but the Martian winds prevented it from detecting any quakes. But studying seismology on Mars could help us understand fundamental questions about the planet’s geology, such as why its magnetic field decreased, and why it doesn’t have geological features similar to Earth’s, which could tell us more about the evolution of terrestrial planets.

washingtonpost.com
Five myths about earthquakes

by renowned seismologist Susan Hough:

  1. Animals sense impending earthquakes: “Every pet owner understands that, say, cats and dogs sometimes behave strangely for no apparent reason; that’s what cats and dogs do. And if an earthquake had not subsequently struck, you can bet we would not be talking about strange animal behavior this week — because we wouldn't have noticed anything out of the ordinary.”
  2. The frequency of large-scale earthquakes has spiked: “The number of earthquakes greater than magnitude 7.0 has been somewhat high in recent years but well within the range throughout the 20th century.”
  3. Small earthquakes are helpful because they release pressure and prevent larger ones: “For each unit increase in magnitude (i.e., going from 5.5 to 6.5), the energy released rises by a factor of about 30. (…) If enough stress has built up on a fault to generate a magnitude-7.0 earthquake, say, it would thus take about 1000 earthquakes with a magnitude of 5.0 to release the equivalent energy. The Earth doesn't work that way. (…) If there is significant strain energy to be released, it must be released in large earthquakes.”
  4. “Don’t worry, it was just an aftershock.”: “The implication is that an aftershock is somehow a less worrisome event. Yet, as far as we understand, an aftershock of a certain magnitude is no different from an independent temblor of a similar magnitude. The shaking and rupture are the same; the energy released is the same. And aftershocks can be more damaging than larger "mainshocks” if they strike closer to population centers.“
  5. Earthquakes are a West Coast problem: "As millions of people on the East Coast were just reminded, less active does not mean inactive. By the end of the 19th century, two of the most notable temblors in the United States were the 1886 quake in Charleston, S.C., and a sequence of large events centered near the boot-heel along the New Madrid Fault of Missouri in 1811-1812. We don’t know exactly when or where the next Big One will hit the United States, but the central and eastern United States will inevitably experience large quakes in the future. (…) You have been warned.”
How Are Earthquakes Measured?

Thanks to the scale at which they take place, natural disasters can be challenging to measure. Consider earthquakes: you can’t ask how high an earthquake is, or quantify the weight of tectonic plates shifting against one another. What seismologists try to do instead is to measure the energy released by a quake, which you can learn all about at the Museum’s Nature’s Fury exhibit.

Aftermath of the San Francisco earthquake, 1906. © Library of Congress

Efforts to detect earthquakes stretch back thousands of years. In 132 CE, Chinese polymath Zhang Heng crafted what is thought to be the first seismic instrument, a bronze vase-shaped device with eight tubes, corresponding to direction points on a compass, protruding from it. When the vase detected an earthquake, the ball would drop from the appropriate tube into a container below, indicating the direction of the quake. Contemporary reports indicate this primitive seismoscope could detect quakes hundreds of miles away, though later attempts to replicate the device couldn’t reproduce this degree of accuracy.

Fast-forward to the 20th century. Most Americans are familiar with the Richter scale, which was developed by seismologist Charles Richter in 1935 at the California Institute of Technology. This scale is based on the largest shock wave recorded by a seismograph 100 km from the earthquake epicenter (the point on Earth’s surface directly above the rupture).

Gurlap CMG3T compact sesimometer, courtesy of Gurlap

Initially devised only to compare the strength of moderate quakes along the San Andreas fault in southern California, the Richter scale was eventually generalized to measure earthquakes all over the world. The Richter scale is logarithmic, with each step up the scale marking a tenfold increase in quake strength—a 4.0 quake on the Richter scale is, for instance, releases 10 times the energy of a 3.0 earthquake. The problem was that for large quakes—over 7.0 on the scale—the Richter scale was less reliable.

In 1979, as geologists developed more accurate techniques for measuring energy release, a new scale replaced the Richter: the moment magnitude, or MW scale, which seeks to measure the energy released by the earthquake. It’s also a logarithmic scale and comparable to Richter for small and medium quakes—a 5.0 on the Richter scale, for example, is also about a 5.0 MW quake—but better-suited to measuring large quakes.

No matter what scale is used, quakes are detected using devices called seismographs, which measure ground motion and produce images showing how these vibrations travel over time. The magnitude of a quake determines how it is classified by organizations such as the U.S. Geological Survey, from  “micro” quakes—the smallest that can be felt by humans—to “great” quakes, which can cause devastation over huge areas.

This post was originally published on the Museum blog

Inge Lehmann

Inge Lehmann was born on May 13, 1888 in Copenhagen, Denmark. Lehmann is best known for using seismic wave data to discover the Earth’s inner core. By studying Primary Waves, she came to the revolutionary conclusion that Earth had a solid inner core, which contradicted the scientific consensus of the time that Earth had a liquid core surrounded by a solid mantle. Upon its publication in 1936, Lehmann’s research was quickly accepted by the scientific community and in 1970, more advanced seismographs were used to prove her theory.

Inge Lehmann died in 1993 at the age of 104.