Category Archives: Earthquakes

Today in Geological History; June 10th – Tarawera

Standard

Today marks the 130th anniversary of Tarawera bursting back to life after 500 years of sleep. It was one of New Zealand’s largest eruptions in recent history and killed up to 150 people making it the countries most deadly since the arrival of the Europeans.

Members of Te Arawa hapu Tuhourangi and Ngati Rangitihi will, weather permitting, make their annual pilgramage to the top of Mt Tarawera today for the 130th anniversary of the eruption.  Photo/File

Tarawara was last active in 1315 and is believed to have had a great hand in the Great Famine of 1315-137 throughout Europe. In 1886 the mountain gave little warning of up coming events. On June 1st a series of waves were recorded on the surface of Lake Tarawera suggesting seismicity in the area although no one reported feeling quakes and there where no seismometers at this time. Tourists claimed they saw a phantom canoe floating across the waters with Maori warriors on board. Although there were multiple accounts on the sighting many believed it was simply a rogue wave caused by increased seismicity, tribal elders at Te Wairoa however claimed that it was a waka wairua (spirit canoe) and was a portent of doom.

Charles-Blomfield-Mount-Tarawera-in-eruption-June-10-1886.jpgAll was quiet again in the following days and people though little of the complex. Many geologists at the time didn’t even consider the edifice to be active due to the lack of solfataric or fumarolic activity in comparison to New Zealand’s other volcanoes.

At 2am local time on June 10th this all changed. Locals where awoken by large tremors shortly followed by explosions heard as far away as Blenheim over 500 km to the south. by 2.30 all three peaks of Tarawera were eruption with fire fountains lighting up the pitch black, ash filled skies. The eruption began to the northeast side and spread rapidly along a fissure from Tarawera to Lake Rotomahana into the Waimangu Valley. The eruption was believed to be caused by a series of basaltic dikes which rose from depth and intersected the very active hydrothermal system under Tarawera and Lake Rotomahana, causing rapid steam/magma explosions, driving the plume that was observed and creating, by some accounts, fire fountains as tall as 2 km which explains the high explosively of a basaltic eruption.

The darkened skys were seen as far as Christchurch and was catapulted in the stratosphere where it lingered effecting climate for at least a year. The ash fall from the eruption – called locally the “Rotomahana Mud” – can be found into the Bay of Plenty almost 40 km away. This tephra covered 15,000 km2 over the North Island and over 4,500 km2 of the area with at least 5 cm of tephra.

The eruption itself produced at least 1.3 km3 of tephra (~0.7 km3 of dense rock equivalent), likely at a rate of higher than 6 x 104 m3/s. It also produced a base surge that travelled over 6 km from the craters moving 40 m/s and were large enough to top hills that were 360 meters tall which buried several Maori villages.

The Buried Village Rotorua

The Buried Village Rotorua is now a popular tourist destination often branded New Zealand’s answer to Pompeii. As well as the human impacts it also buried the Pink and White Terraces.

 

 

Figure 1; http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11653679

Figure 2;  https://en.wikipedia.org/wiki/1886_eruption_of_Mount_Tarawera#/media/File:Charles-Blomfield-Mount-Tarawera-in-eruption-June-10-1886.jpg

Figure 3; http://www.visualitineraries.com/VisitPoint.asp?location=419&title=Rotorua+Museum+of+Art+%26+History

Figure 4; http://www.nzonline.org.nz/nzo/business/the-buried-village-of-te-wairoa-rotorua

 

 

Today in Geological History; April 25th – Nepal Earthquake

Standard

Today marks the one year anniversary of the Nepal Earthquake, sometimes referred to as the Gorka Earthquake where over 8000 people lost their lives. The initial quake, which struck approximately 85 miles west of the capital city, Kathmandu and registered at a magnitude 7.8. The shallow depth of the foci, just 8.2 km, lead to violent shaking which hit the maximum of IX on the Mercalli Intensity Scale.

Figure 1. Probably one of the most iconic pictures showing the rubble which was once a UNESCO world heritage site in Bhaktapur

The main earthquake struck at 11.56 am local time and was followed by a magnitude 6.6 just 34 minutes later. Aftershocks continued every 15-30 minutes for days with many hitting over Mg 4.5 hampering rescue efforts. Then on May 12th an earthquake struck further east along the fault line registering at Mg 7.3 killing an extra 218 people.

The Indian plate is currently crashing in to the Eurasian plate at a rapid rate of 45 mm per year, this is the same motion which has given rise to our planets highest mountains; the Himalayas.

As the Indian plate underthrusts the Eurasian plate it can get stuck leading to build up of stresses in areas which are relieved in the motion of an earthquake. Great Kashmir Earthquake of 2005 which claimed the lives of 87,000 people was  and the 1833 Kathmandu earthquakes were both created by the same build up of stress due to the plate collision.

The earthquake was felt over a vast area spanning 5 countries, but it was rural highland areas of Nepal which were worst affected. Landslide caused some of the worst damage. The Langtang Valley was hit by the largest single loss of life with a avalanche nearly 3 km wide sweeping down and burring an entire village. Smaller settlements on the outskirts of Langtang, such as Chyamki, Thangsyap, and Mundu were also buried. It is thought over 300 people died in the avalanche. The onset of the monsoon season soon after the earthquake killed even more people as the unstable ground was unable to hold up under the heavey rains causing further landslides.

Figure 3. Collapse houses in Sankhu, on the outskirts of Kathmandu

The earthquake also set in motion the deadliest disaster on Mount Everest since it was first conquered by Edmund Hillary in 1953. Everest is 220 km east of the earthquakes epicenter and was in the midst of its peak climbing season. Nearly a thousand people where on or around the worlds highest mountain at the time of the earthquake, including 359 climbers at Base Camp. Avalanches were triggered in several locations including one which originated on the nearby peak of Pumori which swept through South Base Camp through to Khumbu Icefall. 19 bodies were recovered from South Base Camp along with 61 stranded climbers. On 27 April, National Geographic reported the total killed on Everest was 24 although this figure has not been confirmed.

One year on Nepal is still struggling to recover. Thousands of homes were destroyed across many districts of the country, with entire villages flattened, especially those near the epicenter. 90% of the Napalese army were deployed to the region and within a week millions of pounds in aid arrived in aid from accross the globle, but after the initial rescue and clean up that appears to be the end of “relief”.

Capture

Table 1. Number of fatalities by county.

Rubble has been cleared and unstable buildings torn down, but virtually none of the 800,000 destroyed buildings have been rebuilt. According to the Red Cross over 4 million people are living in sub-standard temporary shelter.

With aftershocks still continuing and lack of outside aid it is fear life in the region will never fully recover. Nepal has always been known to be at great risk from tectonic activity in 2013, in an interview with seismologist Vinod Kumar Gaur, The Hindu quoted him as saying, “Calculations show that there is sufficient accumulated energy [in the Main Frontal Thrust], now to produce an 8 magnitude earthquake. I cannot say when. It may not happen tomorrow, but it could possibly happen sometime this century, or wait longer to produce a much larger one.”

Figure 4; The rescue workers ranged from locals to internation aid.

The Nepal earthquake was another stunning example of how some of the poorest countries fair the worst in natural disasters. With little or no building regulations cities like Kathmandu are left exposed and easily torn down by even relatively moderate quakes.

It could be generations before rebuilding truely begins in the region affected by the April 25th earthquake hopefully when the time comes lessons will be learnt and better measures be put in place.

 

Figure 1; http://www.theguardian.com/world/live/2015/apr/26/nepal-earthquake-death-toll-exceeds-1500-rolling-report

Figure 2; http://reliefweb.int/map/nepal/nepal-epicenter-earthquake-25-april-2015

Figure 3; http://www.ibtimes.co.uk/nepal-earthquake-you-cant-rule-out-more-earthquakes-come-1500883

Figure 4; http://abcnews.go.com/International/americans-nepal-describe-massive-earthquake-devastating-aftermath/story?id=30580024

Table 1; https://en.wikipedia.org/wiki/April_2015_Nepal_earthquake

Kyushu Earthquake, Mt Aso and the Relationship between Volcanoes and Earthquakes.

Standard

In the past week the Japanese Island of Kysushu has be ravaged by earthquakes.

2016-04-16Japan is a highly seismic area with noticeable quakes in some areas occurring nearly daily.  But things began to escalate for the Kyushu region on Thursday night when a magnitude 6.5 quake brought several buildings down. As rescue efforts began the region had two more huge after shocks during the night, one over Mg 6 and the other > Mg 5. By midday Friday the death toll stood at 9 with over 800 injured and although the aftershocks kept coming many >Mg 4 people were still being pulled from the rubble. Sadly these events were quite possibly a precursor to something larger.

At 01.25 local time (15.25 GMT) a Mg 7.3 struck just north of Kumamoto just kilometers from the large earthquakes which had already occurred. Much of the seismicity in the Kyushu region is related to the subduction of the Philippine Sea plate at great depth. However this series of earthquakes have occurred at very shallow depths several hundred kilometers northwest of the Ryukyu Trench. They have been cause by strike-slip faulting within the Eurasian plate.

Quake damaged houses in Kumamoto, Japan (16 April 2016)So far 22 more people have been reported dead but this is expected to rise in the coming days with at least 80 people known to betrapped in rubble. 11 of which are trapped in a Tokai university apartment in the town of Minami Aso.

 

The shallowness of the earthquakes means damage to the surface is high and it is not just collapsing building which are a hazard. People have fled the area down stream of a dam which collapsed soon after the earthquake. Landslides in the area have taken out roads and power lines and with heavy rain anticipated over the coming days JMA have advised mudslides will be a huge problem for rescuers.

 

 

 

 

 

 

The seismic problems of Kyushu may have also set in motion another geohazard in the form of Mt Aso. Yesterday one of my favorite volcanology bloggers Eric Klemetti tweeted “Quite a few volcanoes on Kyushu and these earthquakes have been centered near Unzen, Aso, Kirishima. This is NOT to say these earthquakes will trigger any eruptions, but could be worth watching over the next year.” Several hours late JMA reported a small scale eruption at Aso. Smoke plumes have migrated 100 meters above the summit and it is not yet clear if the activity is magmatic (caused by movement of magma towards the surface) or phreatic (steam explosion caused by heating of groundwater).

Eruptions and earthquakes do not always come hand in hand but each one can contribute to the other or not at all depending on the circumstances. One indication a volcano is about to erupt is volcanic tremors; these low frequency earthquakes are usually caused by the migration of magma or changes to magma chamber. Although they are rarely higher than a magnitude 4. On the other side large earth quakes can cause faulting in bed rock which allows magma to exploit a new weakness and find a path to the surface it previously could not intrude on. The same can happen for ground water with faulting caused by a quake allowing it to seep in to geothermal areas it previously did not have access to due to the impermeability of the rock. When earthquakes hit volcanic regions volcano observatories always keep a closer eye on vulnerable or highly active volcanoes as a precaution but it is not always needed.

12965168_193557341031357_783094435_n

The Aso Caldera complex has one of the world’s largest calderas. It is comprised of a 25 km north-south by 18 km east-west Caldera and a central cone group comprised of Mt. Neko, Mt. Taka, Mt. Naka, Mt. Eboshi, and Mt. Kishima. Mt Naka where the eruption has just taken place is the most active with its most recent eruption taking place last October. Although much of Aso’s activity in the past century has been relatively small it has had a violent history with at least 4 VEI 7 events in the past 300,000 years.

It’s is not clear whether the earthquakes in the past few days did trigger the current current eruption but JMA are keeping a close eye on the situation and I will update this page as I know more.

 

 

Figure 1. http://earthquake.usgs.gov/earthquakes/map/

Figure 2; http://www.bbc.co.uk/news/world-asia-36061657

Figure 3; http://www.independent.co.uk/news/world/asia/japan-earthquakes-dozens-reported-dead-injured-second-quake-two-days-a6986931.html

Figure 4; http://mashable.com/2016/04/15/japan-earthquake-landslide-photos/

Today in Geological History – March 27th; The Great Alaskan Earthquake

Standard

The second strongest earthquake ever recorded occurred at 5.36 pm AST (3.46 am 28/03 UTC) on Good Friday in Prince William Sound, Alaska. Registering a massive 9.2 on the moment magnitude scale, it shook the region for 4 and a half minutes and generating a tsunami which propagated through out the Pacific Ocean.

The Pacific Plate moves northward and subducts under the North American plate along the northern edge of the Pacific Ocean creating a highly seismic zone and the explosive volcanics of the Aleutian Islands. On March 27th 1964 the Pacific Plate jolted forward in a megathrust earthquake causing major vertical and horizontal displacement in an area spanning over 250,000  km

At the time of the earthquake Alfred Wegener’s theory of plate tectonics was only just being proven by surveys of the worlds oceans. Although the study of seismology and the several large subduction earthquakes which happened in this era helped prove the theory it meant little was understood about the mechanics of megathrust earthquakes (a termed created in the wake of the Great Alaskan Quake). Earthquake resilient building standards where  at the time and all where unprepared for  the events of the Easter weekend.

At a depth of just 23 km the focus was just 125 km northwest of the states capital Anchorage which took most of the damage.It hit a high of XI on the Mercalli Intensity scale, the second highest mark, indicating the intensity of the shaking experienced in the area. The shaking tore apart buildings and subsidence ripped apart roads. Anchorage was built on sandy bluffs and clay, the earthquake caused a landslide which buried 75 homes. The control tower at Anchorage International airport was reduced to rubble.

139 people lost there lives, mainly due to the tsunami which badly hit much of the Alaskan coastline but also claimed lives as far away as Crescent City, California where 12 were killed. At its maximum the tsunami reached as high as 220 ft in Shoup Bay, but most were much smaller. Alaska was actually hit by multiple tsunami, one caused by the earthquake itself and then several local smaller waves up to hours later prolonging the suffering and hampering rescue operations.

The Great Alaskan Earthquake changed much of our understanding of the sheer power of our planet, which rang like a bell with vibrations for days after. Waterways as far south as Texas sloshed from side to side as the seismic waves where felt throughout the continent.

USGS worked quickly to collect data, recording the subsidence and uplift in the region. They began to see how secondary faults accommodated the erratic displacement. They also began to form a much clearer picture of the Aleutian Trench where the Pacific Plate subducts cementing the idea of plate tectonics. It also shone light on the major part soil liquefaction had in the destruction of the area. Core samples taken along the Copper River indicated that the Good Friday was not the first megathrust event in the area. Analyzing just 50 ft cores scientists revealed evidence of 9 megathrust earthquakes in the past 5,500 years.

The events of March 27th lead to the USGS beginning installation of an extensive earthquake-monitoring network across Alaska as part of the Advanced National Seismic System. In 1966 the National Earthquake Information Center was established as apart of the US Coast and Geodetic Survey and was transferred to USGS control in 1973. By 1977 Congress passed the Earthquake Hazards Reduction Act, the world was beginning to take the threat seriously.

Figure 1; https://www.google.co.uk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=&url=http%3A%2F%2Fwww.theoildrum.com%2Fnode%2F8573&psig=AFQjCNHCK3Uk0lxyjJZhA8t2fmQn_Kq8iQ&ust=1459094529661721

Figure 2; http://earthquake.usgs.gov/earthquakes/events/alaska1964/

Figure 3; http://www.wired.com/2009/07/tsunami/

 

Today in Geological History; March 11th – Tōhoku Earthquake & Tsunami

Standard

 

article-0-0D924D9F000005DC-785_964x591.jpgI am pretty sure I have covered this event before but seeing as today marks the 5 year anniversary of one of the worst natural disasters in the past decade I thought it deserves a much more in depth look. The events of March 11th destroyed the lives of hundreds of thousands of people and claimed the lives of nearly 20,000. For me, it opened my eyes to a world of geohazards and mad me realized this was something I wanted to study and understand so such loss of life would not happen again.

There are three elements to the events of March 11th that I am going to look at here; the earthquake, the tsunami and the Fukushima power plant. Each aspect a huge disaster in on there own but interlinked as they were caused devastation for Japan. 

The Earthquake

Instrumental Intensity Image

Japan is a volcanic island which stretches along where the North American, Pacific, Eurasian and Philippine plates all collide at different points. It is a part of the Pacific Ring of Fire, the world’s most tectonically active area. Practically all of our planets largest and most destructive earthquakes occur along the ring, one of which rocked the east coast of Japan at 2.46 pm JST (5.46am UTC) on March 11th 2011.

The magnitude 9 quake struck at the shallow depth of just 32 km roughly 70 km off the Oshika Peninsular. The area was already alert to seismic activity as several large foreshocks had occurred in the run up including a Mg 7.2 on March 9th and followed by three more above a Mg 6. Of course no one knew these were precursors to something much larger…

Initial reports from JMA and USGS put the March 11th quake at a 7.9 but this had risen first to a 8.8 and then to a 9 before most of the seismic waves had even hit Tokyo 373 km away. Luckily thanks to Japans intense seismic network the countries capital had at least 80 seconds warning before they felt the strong shaking.

The megathrust earthquake occurred where the Pacific Plate subducts beneath the North America Plate. The Pacific Plate moves at a relative speed of roughly 9 mm per year but it is not a smooth decent, tension can build and release in a large snap causing an earthquake. On March 11th this happened in epic style causing over ~50 meters of displacement near the Japan Trench which caused the tsunami which swept across the Sendai planes. The earthquake was so powerful that up to 1.69 meters of co-seismic deformation has permanently altered our planet and affected the Earths tilt shaving 1.8 microseconds of the day (not that we would ever notice!)

It was the forth largest earthquake ever recorded and the largest ever to strike Japan.

The Tsunami 

The displacement on the sea bed in turn caused a huge displacement of water in the Pacific ocean its self. Across a 180 km stretch there was recorded up thrust of 6-8 meters. Above the rupture the tsunami waves would have looked like no more than ripples on the surface radiating out across the ocean. It is as the waves reach the continental shelf and the water is forced upwards that they begin to take on their characteristic ‘wall of water’ appearance.
At its maximum height (recorded at Miyako, Iwate) the waves hit 40.5 m high (133 ft). The Pacific has the most comprehensive tsunami warning systems in the world but even this gave only about 15 minutes warning from the earthquake to waves hitting the coast line. Travelling at speeds up to 500 mph the water surged up to 6 miles (10 km) inland.

Honshu earthquake tsunami travel times

It was not just Japan which felt the repercussions of the event. Tsunami waves propagated out through out the entire Pacific. 11,000 miles away the coast of Chile experienced waves in excess of 2 meters along with most of the America west coast right up through to the Aleutian Islands and as far south as Antarctica where it broke chunks off the Sulzberger Ice Shelf

An estimated 5 million tonnes of debris began washing up on shore lines across the Pacific in the months and even years after the initial Earthquake. In April 2013 a 20 ft boat ran aground in California and was later identified as belonging to the marine sciences program at Takata High School, Japan. NOAA have kept tracks and aimed to clear as much of the debris as possible to minimize risk to ships and wild life but the operation can take more than a decade.

Fukushima

The melt down at the Fukushima was the worst nuclear disaster the world has seen since Chernobyl in 1986.

The plant ran by TEPCO had 3 of its 6 units shut down for inspection when the earthquake struck. Units 1, 2 and 3 then under went automatic shutdown cutting off power. 50 minutes later the waves up to 15 meters high breached the measly 5.7 meters seawalls and flooded the basements of the turbine buildings and disabling the emergency generators. The lack of power meant the cooling systems of the 3 active reactors failed and eventually the heat caused by decay caused the containers to burst leaking radioactive material.

It was classified a Level 7 on the International Nuclear Event Scale (INES) and its was the way the event was handled from the very beginning my TEPCO which saw the escalation in the threat. Approximately 15 PBq of caesium-137 was released along with some 500 PBq of iodine-131, luckily all the failed reactors were in concrete containment vessels, which limited the release of strontium-90, americium-241 and plutonium.

Dozens of vehicles lie abandoned and covered in overgrown bushes along what was once a stretch of road near the power plantNo deaths were caused by the events or short term radiation exposure but it is thought people in the area worst hit will have a slightly higher risk of developing certain cancers in the future. Now 5 years on there is still a 12.5 km is still in place with thousands of people still exiled from their homes. The wild has reclaimed the land making it look like a scene from an apocalyptic film.

It could be centuries before the area is truly deemed safe to live on again.

Pre-Warning; This has happened before

Japan is no stranger to tsunamis; the 1896 and 1933 Sanriku earthquakes (Mg 8.5 and 8.4 respectively) also brought deadly waves. For this reason tsunami barriers have been constructed both on and off shore, trees were planted along the coastline, vertical evacuation buildings were built to the highest standards and regular evacuation training was introduced. But none of these were built to with stand the sheer force of a tsunami of this magnitude.

In 2001 a team from Tohoku University published an article in Journal of Natural Disaster predicting such an event occurring every 800-1100 years. Within the Sendai Plain there is evidence of at least 3 major tsunami deposits all left within the past 3000 years. On July 9th 869 BC what is believed to be a magnitude 8-9 earthquake occurred off the coast of Sanriku causing a major tsunami which left deposits up to 4 km inland. So given that we knew an event like this had occurred before, why was Japan not better prepared for March 11th?

Sadly human nature does not always listen to the reason of science. It is often easier to believe ‘it won’t happen in my life time’ and then brush the threat under the carpet for future generations. The problem is it does not matter how much we study the mechanics of our planet we are still no where near being able to predict these disasters with any degree of accuracy meaning preparation is our best defence.

Aftermath

A report issued by the Japanese government in May 2015 claimed the events of March 11th 2011 caused $300 billion dollars. A confirmed 15,894 people lost their lives, 2,562 people are still unaccounted for.

5 years on the area is yet to recover. An estimated 174,000 are still displaced mainly due to the exclusion zone still heavily in place around the Fukushima plant. Soon as the initial rescue operation was completed the Tohoku Earthquake Tsunami Joint Survey Group was assembled. A team of natural scientists and engineers from 63 universities world wide set out to understand what made this tsunami so powerful and how we can protect our selves from further events. By the end of 2011 the Japanese government had passed laws to establish “tsunami-safe cities” and pledged billions of dollars to an intense 5 year clean up operation. It was clearly a bigger job than they originally thought….

Today there are still over 60,000 people living in temporary accommodation.For residents once living near the Fukushima power plant they will probably never return to there own homes. Sendai is still trying to recover from the tragic events but also now living in fear that this could occur again.

It is for this reason I choose to go in to studying geoscience. We all live at the mercy of our planet and most of us never even consider the risk the land beneath our feet poses. Prediction, preparation and knowledge can save lives and this is what I one day want to help with.

 

Figure 1; http://www.dailymail.co.uk/news/article-1365318/Japan-earthquake-tsunami-The-moment-mother-nature-engulfed-nation.html

Figure 2; http://earthquake.usgs.gov/earthquakes/shakemap/global/shake/c0001xgp/

Figure 3; http://minookatap.com/2011/08/22/japan-book-club-the-big-wave-5/

Figure 4; http://www.livescience.com/39110-japan-2011-earthquake-tsunami-facts.html

Figure 5; https://7plaguesofgod.wordpress.com/2011-tsunami-japan/

Figure6; http://vassarchronicle.com/section/politics/foreign-affairs/lack-of-regulation-fukushima-meltdown/

Figure 7; http://www.dailymail.co.uk/news/article-3263714/Destroyed-man-reclaimed-nature-Amazing-images-reveal-exclusion-zone-Fukushima-abandoned-overgrown-wilderness.html

 

 

 

Volcanoes in Space

Standard

We live on a spectacular, dynamic planet. Geological processes like volcanism and quakes were long thought to be unique to Earth, then again we once thought the planet was flat! As we further our exploration of our solar system and beyond we have witnessed that many other planets display activity from moon quakes to eruptions on distant moons of Jupiter.

https://i2.wp.com/static.wixstatic.com/media/adbce4_e00555b4dd2d4467b8bad585a3250273.jpg_srz_674_518_75_22_0.5_1.2_75_jpg_srz

In June Venus broke in to mainstream media as the ESA announced they had evidence of current volcanic activity on the second planet from the Sun. Venus’s dense atmosphere has long been blamed on a violent eruptive past, but it was thought that this had long since calmed. Then last month NASA released images of Pluto which suggested recent resurfacing, so where is there volcanic activity within our solar system and how does it compare to activity here on Earth? Here is a basic over view of volcanology with our Solar System other than here on Earth.

Mercury

Starting with the planet nearest the  Sun with a small, quiet Mercury. When people first glimpsed at the planets scarred surface instantly it was thought that the impact from meteors or asteroids in the past were the most likely cause. Even when the suggestion was made that volcanism could be a cause for at least some of the topography it was said that the planet did not have the volatiles available for such explosions. These ideas were strongly refuted in 2008 when NASA’s MESSENGER mission began to feed back clearer images of the surface then we had before. They showed clear signs of pyroclastic deposit at 51 sites, all of which showed different degrees of erosion indicating they had happened at varying stages in the planets history. There was also evidence of compressional features such thrust faults leading us to belive that Mercury is more geologically active (or at least has been) then we previously thought.

Venus

Venus’s surface is scared with more volcanic features than any other planet in our solar system. Its dense, toxic atmosphere is believed to be due to the release of volatiles during its explosive past.Huge shields such as Maat Mons and Sapas Mons have appeared reminiscent of those of Earth such as Muana Loa with composition of lavas most likely to be a fluid basaltic or occasional carbonatite. Although some similarities are there Venus shows no sign of tectonic activity such as the liner volcanic chains or subduction arcs we have here on Earth. Volcanism appears to be limited to upwelling similar to hotspots on Earth evident in the large Hawaiian style shields.

Despite all this evidence of volcanism it appeared to have long since ceased until ESA’s Venus Express completed its 8 year mission getting up close and personal with the planet last year.

Radar imagery detected several hot spots along the surface indicating at the very least younger lava flows then we previously thought. It is still open for debate for the age of such flows or if even an eruption or two are taking place up there while I type. The one thing that Venus Express has proved is that activity has occurred in more recent geological time than we had previously thought.

The Moon

Getting closer to home we have our natural satellite, the Moon. It’s surface separated in to two distinct regions; Lunar highland and maria.  The age of the two regions were hinted at by the amount of impact scaring. The older the rock the more impact craters tend to cover its surface; the highlands. The dark patches, visible to even the naked eye, are the maria, volcanic resurfacing of these areas been they are less scared by impacts. Basaltic lava flows dated predominately at 3.8-3.2 Ga, believed to be caused by upwelling in ancient impact basins due to thinness of the crust. Unlike terrestrial basalt, samples from the Mood indicate a much lower SiO2 content (<45%).

Patches reveal recent lunar volcanism

But much like Venus, where we thought things had calmed billions of years ago, in 2014 NASA’s Lunar Reconnaissance Orbiter (LRO) allowed us to see our perception of Lunar volcanism was also potentially wrong. It was perceived volcanism came to a rather abrupt stop roughly 3.2 Ga ago but LRO was able to pick out rock formations and deposits which would not have been visible from Earth. These new features were termed Irregular Mare Patches (IMP). These new images suggest volcanism did not stop abruptly as previously thought, but petered off over millenia ending as little as 100 million years ago.Figure 4 shows one such IMP deposit called Maskelyne indicative of smaller, younger eruptions than what we believed formed the maria in the first place.

This leads to a whole new train of thought when it comes to lunar dynamics. Recent volcanism means the Moon’s interior was hotter for longer then we believed, and if so is it still capable of eruptions?

Io

Io is one of my favourite aspects of extraterrestrial volcanism, and to be fair volcanology in general. Despite only being one of Jupiter’s moons, it claims the title of our Solar Systems most volcanically active body. Io’s most famed images captured a sulphurous eruption column which breached Io’s atmosphere climbing 140 kilometres from the surface from the  Pillan Patera caldera. And also in the centre of the image the Prometheus Plume, a 76 kilometre eruption column which cast and amazing shadow of the surface. The first time the Prometheus Plume was spotted was during the Voyager flybys in 1979. It was then captured several times in exactly the same place at a similar altitude by Galileo during its orbital of Jupiter from 1995 to 2003. This suggests an eruption of continuous intensity for over 18 years!!!

Io: The Prometheus Plume

Volcanism is believed to be driven by strong tidal forces. Io is not only subject to Jupiter’s gravitational pull but also that of two of its other satellites; Europa and Ganymede, both much larger than Io. The surface is full of huge caldera’s and lava flows, much longer that we see on Earth. Magmatic composition is believed to vary from ultramafic basaltic flows to much more sulphur rich melts which lead to flows in excess of 2400  °C. It is thought that as many as 400 active volcanoes cover the surface making it a very explosive environment indeed!

Enceladus

Cryovolcanism is a concept that had been batted around for a while on form or another. A volcano erupts a melt based on the composition of the underlying crust and in some cases mantle. On Earth we have a wide variation of silica based magmas and even the rare instances of carbonatites, but what of an icey body rich in water, ammonia or methane?

When the Voyager missions passed Enceladus in the early 1980’s it was suggested that the satellite may be geologically active due to its smooth surfaces and location close to the E Ring. It wasn’t untill NASA’s Cassini mission in 2005 that proof of cryovolcanism on the body really came to light.

The first detection of the icy plume came on February 17th. Then a second event was witnessed July 14th and this time Cassini flew through the gas cloud enabling on board instruments to tell us the composition; predominately water vapour with traces of nitrogen, methane and carbon dioxide. Visual confirmation came in the November with plumes of icey particles streaming from the bodies south polar region. A subsurface ocean under the south polar region is believed to be the cause of a thermal anomaly in the area which could be fuelling volcanic activity, although tidal heating my also have a hand.

Triton

In 1989 Voyager 2 passed by Neptune’s moon Triton and took images to give us an insight to these far out bodies and managed to find further proof of cryovolcanism in our Solar System. Several geyser like eruptions were spotted with plumes as high as 8 km above the surface. The entire surface looked relatively young with such fewer impact craters than other bodies the mission had encountered, another indication it was very geologically active.

Pluto and Charon

NASA’s New Horizons mission sent back amazing images in July of not only Pluto, but also its satellite Charon. Both exhibited relatively young surfaces, Charon more so than Pluto has huge patches barely dented by impacts suggesting recent resurfacing. Pluto is home to mountainous regions which have be likened to the Earth’s Rocky’s and huge nitrogen filled glaciers. Although no clear evidence of volcanism was seen as of yet, it is obvious that Pluto is more geologically active then we previously thought. It will take another 16 months for all the data collected to return to Earth so in time we may have evidence of at least one or two more volcanic bodies within our system!

There is still much we don’t know about the dynamics of volcanoes, both here on Earth and on other planetary bodies. One thing we can conclude is the further we explore the universe the more we will learn geologically which we can apply to our own planet and equally, exploring our own planets workings can help us understand others.

Figure 1. Painting; http://www.astroart.org/#!volcanoes/c440

Figure 2. Mercury; http://space.stackexchange.com/questions/2302/how-tectonically-active-is-mercury

Figure 3. Venus poster; http://www.esa.int/spaceinimages/Images/2015/06/Evidence_for_active_volcanoes_on_Venus

Figure 4. Moon; http://www.latimes.com/science/sciencenow/la-sci-sn-moon-volcano-recent-nasa-lunar-20141014-story.html

Figure 5. Io; http://www.nasa.gov/multimedia/imagegallery/image_feature_758.html

Figure 6. Enceladus diagram; https://en.wikipedia.org/wiki/Enceladus#Cryovolcanism

Figure 7. Enceladus; https://www.pinterest.com/astrobella/volcanoes-fire-and-ice/

Figure 8. Pluto; http://www.bbc.co.uk/news/science-environment-33543383

What Makes an Earthquake ‘Significant’?

Standard
If you google “What is the definition of a significant earthquake?” you are met with Michigan Tech’s* response; Major – magnitude 7-7.9. However when looking at ‘significant’ earthquakes on the USGS** web page there are ones as low as magnitude 3.3. So to different people (and/or institutions) how we classify earthquakes seems to vary greatly and this occurs from top seismologists right through to media reporting and how we perceive the threat.

 

At 11.23 UTC on May 30th a Mg 7.8 earthquake struck off the coast of Japan. This is the same magnitude as that of Nepal’s April 25th quake but one managed to devastate an entire region and the other barely shook a few skyscrapers. Unless, like my self you concern your selves with the rumblings of our planet, or you live in Japan or the surrounding area you probably did not ever know last Saturdays earthquake even happened.

1. Aftermath of Nepal earthquake April 25th 2015.

The main difference between the two is the location of their foci. The focus of an earthquake (sometimes called the hyprocenter) is often confused with the epicentre, however the epicentre is the surface area directly over where the earthquake takes place, whereas the focus is the actual point at depth where the snap of energy takes place. With the Nepal earthquake the focus was just 15 km under a heavily populated region. The buildings on the surface were poorly built and unable to with stand the violent shaking, bringing them crumbling to the ground killing over 8000 people.

2. Displacement by Japan’s March 11th 2011 earthquake.

The Japan earthquake in contrast occurred off the coast, below the Pacific Ocean, although the some shaking was felt onshore. Many may assume this is safer than an earthquake under an urban area but several of the most deadly earthquakes occur at sea as they can induce tsunamis like that of March 11th 2011 which killed nearly 30,000 in Japan or the infamous Boxing Day Tsunami which killed as many as 230,000! Luckily on Saturday no tsunami alert was even issued, as the biggest difference between these two 7.8 earth quakes is depth.

Occurring at 677 km beneath the surface, this deep-focus (below 300 km) earthquake happened so deep its distance from focus to surface is only slightly shorter than travelling from London to Berlin (690 km)!!! As seismic waves travel they dissipate, loosing energy so are never as intense as what they are closer to the source.

3. Diagram of an earthquake, highlighting its focus and Epicenter.the waves lighten in colour with distance from the focus to show their loss of strength.

 

So so far we have magnitude, depth and location which impact on the devastation potential, but is there any thing else? Well we can expand on the last, location, to highlight other potential threats posed by an earthquake. A moderate sized earthquake in the heart of Los Angeles or Tokyo may stop the subway and send food flying off shop shelves but casualties should be low. The same earthquake in a country like Nepal or Haiti can kill thousands. Earthquakes don’t kill people per say, I have never heard of some on being shaken to death by a quake.What kills people is poorly constructed buildings collapsing, bridges failing, gas mains bursting causing fires. After past disasters such as San Fransisco’s great earthquake of 1906, wealthy countries which sit along active fault lines have put in place strict building codes and pumped millions in to disaster management programs and construction.   Obviously earthquake-proof is not always a possibility by earthquake-resistant definitely is and has saved the lives of many of the past few decades. Sadly not all at risk areas have that luxury of these safe guards at the expense of hundreds of lives.

4. Damage and fires caused by the Greath San Fransisco earthquake in 1906.

Seismology is a tricky business. With so much to take in to consideration when classify earthquakes, it is easy to see where there is often conflicting statements. Things are complicated further by the multitude of scales actually used to quantify them. When asked what scale is used, I can guarantee most will say the Richter scale (or local magnitude, ML), that is even what I was taught in school. Charles Richter first put his scale to use in 1935 to give a more scientific quantification for earthquakes than the previously used Mercalli scale which was solely based of human perspective and building damage (this is still used today but not as often). The Richter scale was limited in many ways being primed for nearby, mid-sized earthquakes (M 3-7). Seismologist Beno Gutenberg expanded on Richter’s work greatly enabling the scale to factor in greater distances and separated scales for surface waves (MS) and body waves (Mb).The revised scales still had difficulties and were particularly ineffective when looking at earthquakes which spanned great lengths of fault lines such the Aleutian Fox Island quake of 1952. The Richter scale was finally replaced by the Moment magnitude scale (MW) back in 1979 and this is the scale used by most institutes today including USGS.

Moment magnitude was born from elastic dislocation theory put forward in 1972 which suggests that energy release from a quake is proportional to the surface area that breaks free, the average distance that the fault is displaced, and the rigidity of the material adjacent to the fault. It is based on a similar logarithmic scale to the Richter scale with each step equating to an increase in the amount of energy released 101.5 ≈ 32 more than the previous. Earthquakes usually have similar Richter and moment magnitude numbers but rarely exactly the same and this can be one way one earthquake can be reported at different levels across the media if their sources used different scales. Another way which causes different figures  is precision; the more seismic stations used to calculate magnitude the more precise the result. When an earthquake is first recorded institutes are likely to only use their own data but as soon as they have access to the global seismic network they can give a more accurate classification. This happen with Japan’s earthquake on May 30th, initial reports put it over a magnitude 8 but this was quickly downgraded to 7.8.

As you can see an earthquakes significance is a matter for debate and in many cases personal opinion. Magnitude and location (not just geographically but also politically) are the main factors but it tends to vary earthquake to earthquake.

Station VRI seismogram

5. Example of a seismograph.