Tectonics Flashcards
(22 cards)
1
Q
EQs Single Fault
A
2004/5 Sumatra EQs
- 26th dec 2004 = 9.3
- 28th march 2005 = 8.7 - caused 2m rock uplift
- large scale - rupture equivalent distance Baltic to Sicily
2
Q
EQ 8+
A
2018 Fiji EQ 8.2
- 19 august
- 0 deaths = good warning systems, didn’t create big tsunami, good infrastructure
3
Q
Stein (2003)
A
- EQ and aftershocks then fault quiet until stress rebuilds - but also idea major shock can cause likelihood to jump of another shock somewhere else on the fault
- stress triggering - faults respond to stresses nearby fault - stress moves down fault = more tremors
- 1/3 aftershocks cluster spatially and temporally and hit along fault of main shock - omori’s law
- what about aftershocks not close to main one? - look changes earth’s crust after major EQs - eg. San Andreas Fault tectonic plates move opposite directions, as do stress exerted parallel to plane fault - perpendicular second stress - stress can’t disappear so after EQ must dissipate somewhere - redistribute along fault or to nearby faults (coulomb stress)
- working with past to apply future - predicted Turkey’s North Anatolian Fault based stress have 7 or larger near Izmit 1997-2027 - 1999 7.4 EQ occurred - now anticipate Istanbul next
4
Q
England and Molnar (1990)
A
- surface uplift = uplift rock - erosion (work against gravity) (rock uplift = surface uplift in presence no erosion)
- raised mountain range surface due to thickening continental crust - but what if uplift not linked crust thickness - thought stress from mantle convection
- measuring uplift = measure change elevation (only reflect surface displacement if no erosion)
- many reported surface uplift mountain ranges too fast to be accounted for crustal thickening rates / do not correlate tectonics - rock uplift often mistaken for surface uplift - problem in using some rock uplift to infer surface elevation change whole region (erosion could greater some areas, different rates depend rock type etc) - erosion reduces crust thickness and so without other influences, surface moves down while individual rocks remaining surface move up
- can have erosion and uplift of land
5
Q
Milliman and Syvitski (1992)
A
- sediment load / yield = function of basin area and max elevation river basin (topography influence sediment load)
- most rivers reflect human activity on their erosional capacity eg. damming, diversions (Nile, Colorado no longer deliver sediment to oceans)
- less runoff with bigger basin area / more runoff with increased yield - bigger basin area thus = lower yield
- sediment yields depend on topography and basin area thus high yields in mountainous areas
6
Q
Clift and Blusztajn (2005)
A
- Indus river sediment mostly from erosion north Indus suture zone until 5mn years ago when shift receive more erosional products Himalayan - change caused reroute rivers Punjab into Indus (flowed into east Ganges before) (shown through switch in isotopic character 5mn yrs ago) - clear increase sedimentation rates Pliocene to Pleistocene during the change - sedimentation accumulation doubled after 5mn years due to enhanced erosion in catchment
- East Asia drainage patterns eastern Tibet suggest Red River originally been ancestral E Asia River, lost drainage neighbouring systems due to long-term topography change
7
Q
Stock and Dietrich (2003)
A
- flowing water sculptures valleys
- think that debris flow valley incision in unglaciated steep lands has an area-slope topographic signature distinct from bedrock river incision - investigation debris flow if imprint topographic signature valley in USA (13 sites) - aim distinguish river-cut valleys to debris-flow cut
- fluvial power law prediction
- found that debris flows occur in landscapes steep enough to produce mass failures - erode bedrock and have topographic signature of a curvature in area-slope space above 0.03-0.10 slope - power law slope and area begins over-predict valley slopes at certain point - where debris flow influence increases rapidly
- much world’s steep land valleys may be cut by debris flows (debris flows = landscape evolution as extensive in length and comprise large fractions of main stem valley relief
- debris flow limit relief of unglaciated mountain ranges
8
Q
Beroza (2012)
A
- great EQ (over mag 8.5) v infrequent - can we really be at risk more big EQs
- EQs cluster eg. seem like more 04/05 Sumatra, Indonesia, Japan etc
- Ormori’s law - frequency aftershocks after large EQs decays inversely w time
- lack data large EQs - eg. from last 100yrs short time establish rarity large EQs (also depends threshold definition large EQ)
- perception more large EQs due to media and hitting vulnerable places like Haiti 2010 (200,000+ deaths) and globalisation
- need understand more about large EQ frequency and EQ processes
9
Q
Malamud (2004)
A
- challenge understand when / where natural hazards will strike - need to understand cause to have chance prediction
- power laws applied to natural hazards - larger magnitude, less frequent, bigger more rare - increasing use governance to assess hazard risk - if not long enough records rely on frequency-size probability distributions
- increasing number hazards being shown to follow heavy tailed distributions similar to power-law distributions
- large EQ rare, small frequent
- landslides, volcanoes and wildfires exhibit power laws
- need to recognise limits to natural phenomenon following these laws eg. may up to a certain point
- not enough data accurate natural hazards prediction but society needs answers so do best can
- need account for clustering of events
10
Q
Shearer and Stark (2012)
A
- fear of increasing large EQs argue unfounded - yes high rate 8+ since 2004 but rates have been almost as high before and small ones rate close historical average
- concern arises from 2011 Tohoku, Japan and 2004 Sumatra etc
- in line Gitenberg-richter power law relationship
- Q of clustering - surplus EQs 1950-65 and 2004-2011 - clustering not stat significant - uncertainty - does not fit omori’s aftershock ideas
- estimated global rate v large (over 9) EQs uncertain as only 5 occurred since 1900
- Risk has not changed high magnitude EQ just our estimates of the risk have changed (perception danger)
11
Q
Bilham et al (2001)
A
- Bhuj EQ India 26 Jan 2001 hazards buildings not designed withstand EQs - not in Himalayan arc where anticipated worse impact, so not prepared
- lot potential areas slip Himalaya, longer between EQ, bigger slip, bigger next EQ
- pop India doubled since last big EQ 1950 Himalayan - 50mn people at risk - Ganges Plain urban pop increased x10 since 1905 EQ
- despite building codes, the percentage population killed similar in 1819 and 2001 EQs (pop increase x10 - yet still 2,000 deaths 1819 vs 19,000 deaths in 2001)
12
Q
Schorlemmer et al (2004)
A
- probabilistic forecasting EQs done by looking past seismicity and extrapolating onto future assuming magnitude-frequency distribution of EQs can be explained by a power-law
- should b value be constant or varying - model predicts v different results
13
Q
Konca et al (2008)
A
Sumatra-Andaman EQ and tsunami 2004
- 2005 march Sunda megathrust ruptured again = 8.6 south 2004 rupture area (site similar event 1861) - concern then on another area where EQ in 1797 and 1833 - two events did occur there a 8.4 and 7.9 sep 2007 - chance another rupture remains large as only fraction area 1833 quake ruptured
- unsure why 2007 not duplicate 1833 event and why released only 25% of moment that had accumulated since then - lack slip cooperation - most likely that seismic asperities not permanent features but move one rupture to another within area
14
Q
Clauset et al (2007)
A
Power-law distributions
- many phenomenon
- difficulty = identifying range over which power-law behaviour holds (tend have differences in tails distribution i.e. large rare events don’t fit law)
- EQs thought power-law distribution - although need favour power-law with a cut off - power-law only feasible for EQs if assume an exponential cut-off that modifies the extreme tail of the distribution
15
Q
Caktu (2013)
A
Istanbul
- unique recognition EQ risk (gov + civilian) and steps taken to mitigate vulnerability
- 1999 Kocaeli EQ - expect next Istanbul = become point research and EQ protection
- 17% Istanbul buildings built after 1999 - EQ design code 1997/07 (thought safe, reality untested)
- developing design codes for high-rise buildings to withstand EQs currently
- need understand socio-economic vulnerability to hazard
16
Q
Audefroy (2011)
A
Haiti (EQ 2010)
- traditional buildings withstood EQ better modern
- highly vulnerable
- majority destruction due poor quality construction materials = structurally weak
- first EQ Haiti with high population density
- building collapse poor soil
- need build community level resilience
17
Q
Joffe et al (2018)
A
- Mitigation favoured over prediction - stigma prediction - eg. 6 scientists convicted manslaughter 2012 inappropriate advice public L’Aquila EQ Italy 2009
- problem of public and scientific conception EQ prediction v different
- seismology as field emerged EQ prediction was the aim of study - but now failure prediction problem
- scientists coming round idea can never predict fully, too uncertain - public lack ideas of impracticality of prediction
18
Q
Garrington (2012) /
Milton (2013)
A
Haiti EQ 2010 (7)
- 200,000 + dead
- GNI $660 per person year
- Remittances 32% GDP 2008
- not recovered 2008 hurricanes - public services already run aid charities and UN
- 70% live on less $2 day
- 70% buildings collapsed Port-au-Prince
- 1.5mn homeless
- 800,000 in 450 camps Port-au-Prince
- twice lethal any previous 7.0 event
19
Q
Hobson (2015)
A
Christchurch EQ 2010/11
- 2010 Christchurch EQ 7.1 no deaths, 6,000 buildings damaged
- feb 2011 Christchurch aftershock 6.3 - 183 deaths
- power restored 95% households in 2 weeks
- Gov plan - the Blueprint for recovery - creation central business district - old heritage buildings like cathedral uncertain future
- Disaster Capitalism (Klein, 2007)
20
Q
Parsons (2006) /
Brighty
A
Asian Tsunami 26 Dec 2004
- EQ mag 9 = Indian Ocean tsunami
- tsunami split two - westbound Bay of Bengal to India and Sri Lanka and eastbound to Thailand
- 32m run up height
- destruction coastal towns
- Maldives whole islands uninhabitable
- coral damage
- 35,000 dead
- 552,641 injured or displaced
- 100,000 houses damaged
- Sri Lanka v vulnerable as no experience tsunamis, population unaware, no early warning system, most live close coast, south and east population poor
21
Q
Holden (2012)
A
- Structure Earth - core, mantle, lithosphere, asthenosphere, crust
- Plate Tectonics + Plate boundaries - divergent (plates pull apart), transform faults (two plates slide alongside), convergent, subduction, hot spots
22
Q
Reid (1906)
A
Came up with Earthquake cycle
