Earthquakes and volcanoes and rocks, oh my!Q: Are volcanoes and earthquakes related?
Humans see volcanoes and earthquakes as two different types of natural disasters but they often can be closely related. Both are part of the plate tectonic cycle. Volcanic eruptions or magma activities can trigger numerous earthquakes and micro-earthquakes (earthquakes of very small magnitudes), many of which are imperceptible to human beings but can be recorded by seismometers. In fact, scientists can monitor or predict the imminent eruption of a volcano based on the sharp changes in numbers of earthquakes recorded around the volcano. Just as volcanic activities can trigger earthquakes, theoretically earthquakes can alter the subsurface stress field and trigger volcanic eruptions as well. But these are rare scenarios because there are far fewer active volcanoes on the Earth today than the number of earthquake events that occur each day. --------------------------- Name of answerer: Chun-Feng Li When speaking of an earthquake, we need three basic parameters to quantify it. They are location, time, and magnitude. First of all, large earthquakes (magnitude > 7) are rare events. However, there are many localized active zones (i.e., subduction zones, oceanic ridges, fault zones) on the Earth where large earthquakes occur almost periodically. These zones are highly hazardous, and scientists have made large research efforts and have already gained a reasonably good understanding of them. If we know the recurrent time interval of large earthquakes on these zones and if we also know the time when the last large earthquake occurred, we can estimate the time period when the next large earthquake will occur. For example, in the part of the Nankai Trough area that we are studying, scientists have learned that the recurrence interval between two large earthquakes is about 100-200 years, and we also know the last large earthquake happened in 1944 and 1946 in this area. Therefore we estimate that there is a very high chance that the next large earthquake will occur in this area in this century. Although we may know the approximate time period when a large earthquake will occur in an earthquake active zone, we are yet unable to pinpoint the exact second or hour and the exact location of the next large earthquake. Our current understanding of earthquakes has not reached a level that can allow us to accurately predict future earthquakes. This is why we are making an international effort (the IODP NanTroSEIZE project) here drilling into the subduction zone along the Nankai Trough. --------------------------- Q: What was the largest earthquake that ever happened? Dean Name of Answerer: Xixi Zhao
It was the 1960 Q: How is the gravity in the center of the Earth? Shin Name of answerer: Xixi Zhao It should be zero. The gravitational pull from every side is
exactly counteracted by that from the opposite side at the same time. Q: Has the size of the Earth been changing since a hundred million years ago?
Name of answerer: Xixi Zhao This is a controversial question.
Some scholars believe the Earth has been expanding and growing rapidly by
external accretion of cosmic dust and meteorites and internal expansion of the
core. Others suggest Earth’s surface has been shrinking due to movement of
plates (subduction) or climate changes. However, these changes are
so small that people standing on Earth’s surface cannot see them. Q: Are there aliens below the seafloor from a
biological point of view? If yes, what kind of people are they? Name of answerer: Fumio Inagaki
The deep subsurface on the Earth had long been
believed to be a place where life could not exist, but recently a tremendous
number of microorganisms have been found in deep marine sediments. These
sub-seafloor organisms are very small, less than 0.001 mm in diameter. They are
very different types of microbes from terrestrial ones, however, you don't have
to worry about that. They grow extremely slowly, each generation thought to be
over 1,000 years. But their activities in the geologic timescale are thought to
play an important role our planet by cycling elements through the crust. The
sub-seafloor life and bioshere remain largely unknown, so that scientists are
now investigating them using samples taken by the Chikyu. Q: What is the oldest layer of rock that you have collected? Name: Daniel Name of answerer: Xixi Zhao The oldest rock layer we have drilled so far is
several million years old. We know that by studying the record of calcareous
nannofossils (tiny fossils found in the cores) and geomagnetic field directions
that were preserved when the rock layer was deposited. In the geologic time
scale, this age is within the early Pliocene period (the word Pliocene is from
the Greek word, pleion, meaning ‘more’). So far, we have drilled about 400 meters below the seafloor and have reached the so-called “Lower Pliocene,”several million years ago. In our second site, we plan to drill down to 1000 meters below the seafloor; we are now at around 400 meters and sediment samples indicate a younger age (around 1,000,000 years). Amongst the techniques we use to date the sediments, we look at two microfossil groups. The most useful and abundant in this area of the ocean are nannofossils, very tiny microorganisms (200 times smaller than a millimeter) with a calcareous shell. They are so tiny that we need a microscope with a high magnification (100 times) to see them. We also look at radiolarians that are also small organisms made of opal (a mineral similar to quartz). Their size can vary from 40 to 300 micrometers (3 to 25 times smaller than a millimeter). Radiolarians are much bigger than nannofossils but if you look at them without a microscope, they would appear like very small sand grains. Many species from both microorganism groups are still living in today’s oceans, but the living species are different from the species that were living a few million years ago. Through time, they have changed their shape, became extinct, or new species have appeared. Scientists have been working for decades throughout the ocean, looking at sediments from all ages to find out when a species has appeared and disappeared. They came up with charts indicating the time intervals where you find particular species of microfossils. Based on these charts and the species that are present or absent in the sediments, we can tell the age of the sediment. It is really useful to use several different species to date the sediments, because it is possible that one microfossil group is missing or we don’t find a good species to establish an age.
Stylatractus universus, a radiolarian species that became extinct a few hundred thousands years ago (magnification 400 times) --------- Q: How do you get oil from the bottom of the sea and what do you use to get
Name of Answerer: Dr. Liz Screaton Answer: In NanTroSEIZE (this set of expeditions), we are drilling to understand earthquakes. So during this expedition, we are getting cores from beneath the ocean floor in order to understand how rocks moving past each other create earthquakes. The ship we use is a lot like ships used to explore for oil. The difference is that we are drilling in a different geologic area. For oil exploration, it is good to look in areas where sediment with a lot of organic matter (former living things) has fallen to the bottom of the ocean and been buried quickly. To understand earthquakes, we are drilling in a subduction zone, where one of the Earth’s tectonic plates is sliding underneath another plate.
---------------------------------------
Name: Rock Lady Name of Answerer: Arito Sakaguchi
Answer: The submarine faults (zones where rocks are sliding past each other) that we are studying are very far from our homes on land. But these types of faults repeatedly cause large earthquakes. The earthquake energy released from plate subduction zones is over 85% of all earthquake energy in the shallow Earth's crust. Also, submarine faults cause “tsunamis;” tsunamis occur when the sudden movement along the fault lifts or drops part of the ocean floor, creating a large wave. These waves can cause serious disasters. Research on submarine faults is important for earthquake sciences and disaster prevention. The collection of cores from this submarine fault zone will give us clues so we can understand how earthquakes occur. ---------------------------------------------------- Q: How are earthquakes formed? How do earthquakes stop? Name of Answerer: Xixi Zhao Answer: Earthquakes occur as a result of a build up of pressure between colliding sections of the Earth's crust, called “plates.” These plates “float” on the mantle like rafts, with a typical speed of a few centimeters per year (about as fast as your fingernails grow). Where we are drilling now, one plate is sliding underneath another plate, in what is called a subduction zone. When the plates “stick” in spots, rather than smoothly sliding past each other, these spots can accumulate tremendous pressure which is released abruptly when the rocks finally break. This release of energy travels through the Earth's crust and causes the shaking that we feel during earthquakes. Earthquakes stop after all the stored energy is released, or the plates “stick” in another spot. --------------------------------------- Q: What is the main rock or mineral that you find while drilling in the ocean? Name of Answerer: Kitty Milliken Specialty and role: Sedimentologist; I work to describe the appearance and composition of the cores. Answer: --------------------------------------- Q: What would happen if an earthquake occurred while you were drilling? --------------------------------------- Q: Will you cause an earthquake?
------------------------- | |
