Earthquakes & Volcanic Studies (Kobe! Fuji!)

Earthquakes& a case study of the Great Hanshin

Earthquake (Kobe)

By Jasmine and Melody310 ‘06

Kobe: The Story

• Formally known as the South Hyogo Earthquake• Other names include Hyogo-ken Nanbu & Kobe

• Struck western Japan at 0546 hours, January 17, 1995

• Lasted about 20 seconds• Devastation was the worst in the port city of Kobe• 7.2 magnitude quake toppled roadways, wrecked

docks, severed communication lines and left the city in flames into the next day

• killed almost 6500 people

Why? (Investigation of Cause)

• Japan’s precarious position upon 3 plates, formed by molten magma from the Phillipines plate• Subducting Phillipines sea plate• Subducting Pacific plate Under Eurasian continental plate

• Friction resulting from colliding on destructive margin• Seismic energy from collisions

is eventually released through earthquakes

• Subduction happening about 10 cm per year

Why? (Geological Conditions)

• Kobe was located slightly off the Median Tectonic line, a zone of strike-slip faults

• Focus was 16km below Awaji-shima, an island in the Japan Inland Sea, close to Kobe

• Shallow focus and probable surface ruptures• Kobe, a low-lying port city, was situated on soft, wet

ground• Constructed on 2 artificial islands of water-saturated loose

fill• High potential of ground liquefying, suspending & loosening

sand, with ground unable to bear weight & buildings collapsing

Why? (Human Conditions)

• Kobe was an older city with residential infrastructure built with wood on the bottom and heavy tiles as roofs• Created more shear force than frame could resist (1.1, 1.2)

• Old infrastructure codes allowed weaker superstructures at 5th floor• Thus some buildings sunk in at 5th floor (1.3)

• Most infrastructure were old & built before strict seismic codes in 1980s

• Lifelines constructed in the 60s and 70s, before modern construction practices• Debris choked streets & rescue work was delayed. Fires were

widespread, making it more deadly

1.1

1.2

1.3

Why? (Cont’d) & Effects..

• Older reinforced concrete structures• Vertical steel rods were unable to preserve structure

from horizontal shaking forces (2.1)• The Hanshin Expressway fell on its side (2.2)

• Soft soil, bad infrastructure?• Subways sunk in, luckily as it was early morning so

nobody was killed (2.3)• Soft, saturated soil [liquefaction]

• Broken gas lines• Fires ensued, killing those who survived the quake &

slowed rescue work (2.4)

2.12.2

2.3

2.4

Ouch! (Some More Serious Effects)

• 300,000 made homeless, requiring shelter• People squeezed into public buildings like schools and town halls• Overcrowded, unsanitary• Lack of food, clean water & medical supplies

• Jan 17th – cold winter, at temp. of -2 degrees Celsius• Hanshin Expressway closed, 130 km of subway closed

• Transport impaired, interrupting trade and commerce• Disrupted school, unemployment, etc

• 120 out of 150 cranes at shipyard fell, destroying goods and ships

• 3-5% of Japan’s economy located near/at Kobe• Shipbuilding, steelworks are just some that got affected

So What Next? (Coping With Problems)

• Water, gas, electricity were restored within half a year• Railways back in service by August• 134,000 housing units constructed, although some people

still lived in temporary accommodation• New laws passed to make buildings

more earthquake-proof• More instruments installed in

area to monitor earthquake movements• However, Japanese government was heavily criticized

• WE ARE POLITICALLY CORRECT & DIPLOMATIC HAHA• (slow, uncoordinated, badly equipped, refused foreign relief)

What is an earthquake?

A Sudden,

Violent,

& (sometimes) Catastrophic movement of a part of the Earth's surface

Causes of Earthquakes• Rocks in earth are elastic, may store mechanical

energy same way a spring does• Rock gives way, cracks when forces are applied strong

enough that they exceed the strength of the weakest part of the solid rock

• These forces include convectional currents that cause our plate movements

• Strain energy is relieved, forces are accommodated by sudden dislocation of rocks on either side of crack

• Releasing of energy and dislocation of rocks is called ‘elastic rebound’

Causes of Earthquakes (cont’d)

• At it’s source (or focus), movement may be over in a few seconds

• However, resulting huge amount of energy released travels through rocks of the crust in seismic waves

• The crack marking the dislocation is known as a fault.

• Following an earthquake (the displacement of the rocks), the rocks on either side come to rest in new positions

Causes of Earthquakes (cont’d)

• These rocks are held in place as a result of friction acting on the rough surfaces of the rocks as well as other forces exerted upon them from the crust

• The stresses and strains that caused the original earthquake continue, and eventually break the ‘frictional lock’ to cause another earthquake

Seismic Gap theory

• A theory that was developed to explain the regular occurrence of earthquakes in certain places

• For example, Parkfield, which has produced magnitude 6 earthquakes every 20-30 years

• Idea – since plates are moving all the time at a steady rate, and since that is what causes the earthquakes;

• …we should be able to predict the occurrence of earthquakes based on when and where they have occurred in the past.

Effects of Earthquakes• Varies from earthquake to earthquake• Mainly includes the ground shaking, and in more serious

cases damage to and destruction of infrastructure• As well as tsunamis in port cities• Fires as a result of the collapse of buildings & broken gas

pipes• Loss of life; especially in large cities• Divided into Primary & Secondary,

• Primary ones - deformation of ground near the fault (immediate collapse of buildings, roads)

• Secondary ones - result from seismic waves away from fault rupture (fire, aftershocks, homelessness)

Primary Effects

• Formation of fault-scarps• Collapse of existing structures, both natural and man-made• Formation of ‘sand boils’, different types of shock wave

vibrations can cause sand and water to spurt out in little cones that look like miniature volcanoes and may reach up to 30cm high• In rare cases, streams diverted (due to fault scarps)

• Liquefaction –shaking increases underground water pressure and water invades all interstices on the sandy silt. • Buildings often sink• Common cause to countless lives lost in devastating earthquakes,

e.g. San Francisco, Messina and Reggio di Calabria as well as Kobe.

Secondary Effects

• Landslides• Changes in the level of the land• Flooding; whereby the debris blocks up drainage systems• Water-borne diseases as a result of flooding

• Cholera, typhoid, dengue• Lack of basic necessities such as food, potable water and

basic sanitary needs• Holdups in transport and communications

• Leads to more deaths as it delays the rescue of people trapped in the debris

Measuring Earthquakes

• The Richter Scale• Based on the size, or amplitude of the waves traced by

the pen on a seismograph

• Seismographs had to be standardized to allow for a fair comparison

• Based on complex mathematical formulas• However it tells us little about the effect of

earthquakes on human lives

Measuring Earthquakes (cont’d)

• The Mercalli Scale: the intensity of an earthquake is assessed by subjective and qualitative observations of the landscape and environment

• Unlike the Richter scale; not based on mathematical calculations

• Calculates the degree of damage done (in a scale of I-XII) based on timing and site of occurrence

• E.g. An earthquake of magnitude 8.4 (Richter) may cause relatively little damage in a sparsely populated area as compared to an earthquake of magnitude 5.8 that occurs in a town

Measuring Earthquakes (cont’d)

• Other factors that affect intensity of the damage includes distance of the settlement in question to the epicenter

• Settlements built on reclaimed land, or soft, water-saturated materials such as silt, would also be at higher risk as silt magnifies ground motion by as much as 75 times

Volcanoes& a case study of Fuji-san

By Jasmine and Melody310 ‘06

Fujiyama: The Story• Actually made up of three different volcanoes; Ko-mitake,

Ko-Fuji (Older Fuji Volcano) and the present Shin-Fuji (Younger Fuji Volcano) which lie one upon the other. • Ko-Mitake – has been dormant since 100 thousand years ago.• Ko-Fuji – which formed the

base of the current Mount Fuji, was active between 100,000 &10,000 years ago.

• Shin-Fuji – which is responsible for the mountain’s current shape, started to erupt about 10 thousand years ago continued erupting repeatedly over 100 times during a period of about 10 thousand years.

!!!!

Flank resulted from last eruption.Fuji isn’t TOTALLY symmetrical.

Fujiyama: The Story (cont’d)

• Studded with more than 100 parasitic cones and flank openings although most of them are too small to be seen.

• Dimensions: about 3776 m above sea level, 50 km across the base with a circular crater of about 500m across

• Archetype of the stratovolcano• Also known as composite volcanoes composed of lava flows

& lahar in alternate layers.• Fuji erupted at least 16 times since 781 AD. Most of these

eruptions were moderate to moderate-large in size • Two largest eruptions to date were in 1050 and 930 BC

Fujiyama: The 1707 eruption

• Latest Eruption: 1707-1708, where 0.8 cubic km of ash, blocks, and bombs was ejected

• Eruption started December 16 and ended about February 24, 1708

• This flank eruption was explosive and generated mudflows

• It caused damage, but according to‘Volcanoes of the World’, there wereno fatalities.

What is a Volcano?

• In basic terms, a volcano is a hole in the earth’s crust, on land or on the sea floor, from which materials are expelled naturally from below.

What is a Volcano? (cont’d)

• These (pyroclastic) ‘materials’ may include hot lava, cinders, blocks, ash or pumice, cold rock fragments of all sizes, aerosols, steam and water.

• Some materials cool and pile up around the hole, or chimney, and often form a cone shaped hill (composite)

• Other fine materials (lahar) can be blasted into the stratosphere, carried around the world, and may remain as aerosols that veil the sun for several years. (Mt. Krakatoa)

The Mafic Cone (ooh, runny!)• Low silica content (~50%)• High Fe and Mg content• Relatively less viscous (hence the runny-

ness)• Travels relatively faster, able to cover

distance of 150km before stopping to solidify• Low-level of explosivity

• Because less gas escapes and hence, little vesiculation

• Low gradient due to slow drying of lava

The Felsic Cone (look at the gas!)

• High silica content (~70%)• Low Fe and Mg content• Relatively more viscous

• Hence moves at slower speeds• Often explodes violently, producing large

amounts of aerosols and fahar• Gas escapes; causes viscosity to increase• Vesiculation is initiated; may trigger an

explosive volcanic eruption• Steep gradient due to viscosity

Formation of a Volcano

• Generated by eruption of magma through a planet's surface; molten rock welling up from the planet's interior

• Magma wells up due to tectonic activity in the plates – e.g. when plates converge or diverge – causing either constructive, destructive or transform plate boundaries.

Formation (types of plate boundaries)

• Constructive• The most common• The least visible (usually occur at considerable depths

underwater)• Cause the formation of a mid-ocean ridge• E.g. the Mid-Atlantic Rift• May sometimes lead to volcanoes reaching the surface

– e.g. St. Helena

Formation (types of plate boundaries)

• Destructive• The most visible and well-known• Form above the subduction zones, where oceanic plates

subduct under the lighter continental plates• Cause the formation of subduction volcanoes• E.g. the Nazca plate diving under the South-American

plate caused the formation of the Andes range

Formation (Hotspots)• Originally generalization for volcanoes that didn't fit into one

of the above two categories • Refers to more specific circumstance today - where an

isolated plume of hot mantle material hits the underside of the crust.• Mantle plume can lead to volcanic center that’s not obviously

connected with a plate margin • E.g. Hawaiian Islands

• Generated by a hotspot underneath the oceanic crust of the Pacific

• E.g. 2: Yellowstone• In this case involves continental crust

(Iceland may also be considered, but the coincidence of a hotspot intersecting a oceanic ridge constructive margin complicates things. )

Primary Effects

• Phreatic eruptions (steam-generated eruptions) • Explosive eruption of high-silica lava (e.g., dacite &

rhyolite) • Effusive eruption of low-silica lava (e.g., basalt) • Pyroclastic flows • Lahars (debris flow) • Fumarolic activity (gaseous emissions, e.g. H20,

C02, S02, mainly, with lesser toxic gases HCl, HF, H2SO4, H2S)

Secondary Effects

• Earthquakes• Hot springs• Fumaroles• Mud pots• Geysers

*Low-magnitude earthquakes often precede eruptions.(that’s like Mother Nature’s forewarning)

Measuring Volcanoes

Volcanologists monitor the following phenomena to help forecast eruptions:

• Seismicity• Seismic activity – or earthquakes etc, is observed

• Gas Emissions• Magma nears surface,

pressure decreases, gas escapes• Sulphur dioxide (main

component of volcanic gases, increasing amounts of it herald arrival of increasing amounts of magma near surface)

Sampling volcanic gasesin an evacuated flask.

Measuring Volcanoes• Ground Deformation

• Swelling of volcano signals magma has accumulated near surface.

• Tilt of volcanoes’ slope• Mapped, rate of swelling tracked in order to help predict

eruptions• Increased rate of swelling, accompanied by increase in

sulphur dioxide emissions & harmonic tremors is a high probability sign of eruption

• Deformation of Mount St. Helens prior to the May 18, 1980 eruption is another classic example of deformation

• Most cases of ground deformation are usually detectable only by sophisicated equipment used by scientists

Eruption Styles

• Four main eruption styles: Hawaiian, Strombolian, Vulcanian and Pelean, after best known volcanoes of each group

• Mild eruptions• Limited to emissions of gas, steam, hot water, sulphurous fumes

and bubbling mud from geysers, hissing holes and fissures.• May be common on dormant or dying volcanoes

• Moderate eruptions• Expel lava and some gas – lava usually basic, basaltic• Occur on fissures• Most common kind of eruption – not usually very dangerous

Eruption Style (Hawaiian)

• Magma rises in a central vent• Thin flows of basalt emerges and spreads over a wide area• Volcano ‘grows’ as each eruption piles on a new layer

• Lava flows may also emerge from vents on either side of the summit, in flank eruptions (Fuji!)

• Characteristically broad-based shape – ‘shield volcano’

• Erupts relatively often• Usually non-explosive in nature• Destructive but slow-moving flows

Eruption Style (Strombolian)

• Constant, but usually short lived moderate activity• Usually cinder cones with a shallow, bowl-shaped crater

• Cinder cones: molten fragmentssettle on cones and embers cool

– eventually many layers are created after constant repeating of this process

• Dust and ash released into atmosphere (lahar)• Lava flows are initially fast-moving, but eventually slow

down

Eruption Style (Vulcanian)

• Vigorous eruptions• More explosive than moderate eruptions as they often contain a

strong element of gas or steam• Gases escape from rising magmas that are viscous and

silicic – large black cloud of ash and steam• Sudden eruptions – quick successions of explosions shatter

fragments off the volcano, shooting them from the chimney• May be followed by several days of total calm until eruptive

spasm is over• Although mostly basaltic, lava flows are often viscous• Larger cinder cones than strombolian counterparts

• Craters are large and deep

Eruption Style (Pelean)

• Viscous, silicic magma rises• Gases in magma separate into bubbles and, near the top of

the chimney, blow the magma into smithereens, forcing a lot of volcanic material of all sizes to be blown out

• Whole mass may be as hot as 700 degrees Celsius• Nuees ardentes – incandescent clouds – are formed

• Made up of gases and fine ash mixed with larger fragments as it rolls down slope, picking up more as it goes along

• Eruptions may be short (2-3mins) but lethal as a result of the nuees ardentes

• At same time, magma surges up forming a lava dome – usually able to withstand minor gas explosions• However may crumble as a result of poor support, and form small

blasts of nuees ardentes

Bibliography• Kobe Earthquake

• http://www.vibrationdata.com/earthquakes/kobe.htm • http://www.ce.washington.edu/~liquefaction/html/quakes/kobe/kobe.html • http://www.seismo.unr.edu/ftp/pub/louie/class/100/effects-kobe.html

• Earthquakes• http://wikipedia.org• http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/

earthquake_effects.html• Mt. Fuji

• http://www.sacredland.org/world_sites_pages/Fuji.html • http://volcano.und.nodak.edu/vwdocs/volc_images/img_fuji.html • http://staff.aist.go.jp/a-takada/Fujiproject-e.html • http://staff.aist.go.jp/a-takada/recentpresent-e.html

• Volcanoes• http://www.geology.sdsu.edu/how_volcanoes_work/Controls.html• http://piru.alexandria.ucsb.edu/~tierney/lectures/geology.htm• http://www2.umt.edu/Geology/faculty/hendrix/g100/L6A.html

• Savage Earth

AND HAHA BYEBYE SEE YOU!BE CAREFUL OF EARTHQUAKES!

And volcanoes too, heh.