Monday, October 22, 2018

Slow Slip and Fluid Drainage could be a Reason for Megathrust Earthquakes

Megathrust Earthquakes
The most powerful earthquakes are the Megathrust Earthquakes that occur at the subduction zones. Here we see one tectonic plate is pushed below the other. On the other hand, there is the slow slip events (SSEs) which release seismic stress at a much lower rate as compared with the large earthquakes. These occur in a cyclical manner across months to years. These SSEs can occur along the megathrust or any other areas which experience weakness due to loading. As a result, there can be release of low frequency seismic waves.

How the fluid which drainsfrom the SSEs can influenceseismic activity has been a topic of research for scientists fromthe Tokyo Institute of Technology and Tohoku University.

Impact of Fluid Drainage on Megathrust earthquakes

It is known that when megathrust earthquakes occur, the megathrusts open up. The fluid that drains out from the megathrusts is due to deformation. Not much is known whether the fluid movements that occur is due to the SSEs or not.

According to professor Junichi Nakajima at Tokyo Institute of Technology and associate professor Naoki Uchida at Tohoku University, the megathrust seismic activity can also be due to the fluid draining from the slow slip.

In order to find whether there is a relationship between SSEs and seismic activities, they have conducted various studies with regard to the seismic activities that occur around the Philippine Sea Plate. They found that the boundary of the plate is where the earthquakes occurred time and again. They also found a relationship between seismic activity and estimated slip-rates. From this they concluded that the seismic activity that was seen above the megathrust of the Philippine Sea Plate kept changing according to the episodic cycles of the SSEs. There was a great amount of draining during the SSEs which occurred every year together with fluid draining into the overlying plate.

The researchers have studied waveform data from beneath Kanto, Japan from 2004 to 2015. Their analysis has been published in Nature Geoscience.

They have explained the role of pore-fluid pressure. The areas of slow slip have high pore-fluid pressure and hence are able to release the fluid into the other areas of the rock. The SSEs could cause the fluid to flow into the overlying rock areas if there was a fracture or a space in the rock bodies. This in turn will cause weakness in those areas resulting in earthquakes.

On the other hand, if there were no fractures or open spaces on the overlying plate, then it would not be possible for the fluid to move into it. The fluid would then be forced on to the megathrust area. This could eventually trigger megathrust earthquakes. From this they inferred that the slow slip could be a catalyst in triggering megathrust earthquakes.

Though stress modulation is a major contributory factor for the megathrust earthquakes, the fluid that flows due to the episodic SSE may also play an important role than what was believed earlier.

Wednesday, October 10, 2018

Scientists Develop New Strategies to Discover Life Beyond Earth

Life Beyond Earth

Scientists look for new ways to Discover Life beyond Earth

The search for life on planets other than our own has been a long and continuing one. At first planets within our own solar system have been checked to see if they had life beyond earth or could in fact support life. Since then scientists have trained their sights on planets that revolve around stars other than our very own sun. Such planets are called exoplanets and with the developments in technology, scientists have found new methods and technologies that could help them detect life beyond earth.

Researchers around the globe have now given a roadmap to discovering life beyond earth which is documented in 5 papers published in a journal called Astrobiology. The papers detail how scientists can look for life beyond earth using telescopes.

Looking for life beyond our solar system:

The first exoplanet was found years ago in 1992 and since then the pace of discovering more exoplanets has increased drastically. At present at least 3,500 exoplanets have been discovered since the first in 1992.

Therefore steps were required to see if these planets and others like it could support life or maybe even have life beyond earth. Scientists around the world have been called in to share their knowledge and combine resources to aid in the search for life beyond earth.

NASA’s Nexus for Exoplanet System Science (NExSS) has done just that. The international network started three years ago, has got scientists from various disciplines to establish signs of life beyond earth as well as look for life on these exoplanets.

Results of NASA’s NExSS in discovering life beyond earth:

The work of NASA’s network is an ongoing effort of scientists and at present has resulted in papers detailing the past, present and future on how to look for life beyond earth. The papers are the work of scientists for over two years and consist of the work of scientists form various fields including astrophysics, biology, chemistry, heliophysics, planetary science and earth science. These papers formed what is contained in the astrobiology journal.

What does the astrobiology papers detail?

Besides detailing how to look for life beyond earth, these papers contain details of issues faced and how scientists are working to resolve them or have already resolved them.

Apart from this, the papers also contain details of two major signals that scientists look for when searching for life beyond earth. One has to do with looking for gases being produced on the exoplanet, such as oxygen, made either by plants or microbes. The second signal has to do with looking for the light reflected off of living beings for example the color of leaves.

Looking for mixed signals:

Researchers are also setting up signals to identify when an exoplanet actually has got life but shows no signs of it and vice versa.

There may be cases where oxygen maybe produced without the existence of life or there maybe cases where life exists on an exoplanet but without any biosignatures being given off from that planet.