Geology 3120 - The Scientific Method and Modelsgeode.colorado.edu/.../coursenotes/3120lect_3.pdf · 2005-08-29 · Geology 3120 - The Scientific Method and Models ... • Deformation

Geology 3120 Geology 3120 --The Scientific Method and ModelsThe Scientific Method and Models

Nonconformity: Contact corner on Flagstaff Mtn

The Scientific MethodThe Scientific Method

• Identify the problem

• Research and evaluate

• Develop a multiple working hypothesis

• Challenge the hypothesis

• Modify the hypothesis or experiment

1. Identify the problem1. Identify the problem

• Personal discovery or a request by another

• Ask the key question!

• Identify resources

• Formulate a plan

2. Research and evaluate2. Research and evaluate

• Literature review

• Empirical data (stuff we can see, existing examples)

• Theoretical modeling

3. Develop a multiple working hypothesis3. Develop a multiple working hypothesis

• A hypothesis is a general statement and an idea that has not yet been proven

• If faced with data that could be explained with several ideas, formulate a multiple working hypothesis so you do not force a conclusion

• Ideas are like children, you’re not supposed to favor one above another!

4. Challenge the hypothesis4. Challenge the hypothesis

• If the hypothesis is correct, your problem can be solved

• A hypothesis must be designed to be tested

• For a multiple working hypothesis, many aspects of interdisciplinary earth science may be explored/tested

• Use empirical or observational data to challenge the hypothesis

• Untestable hypotheses don’t constitute science!

5. Modify the hypothesis or experiment5. Modify the hypothesis or experiment

• If the hypothesis is not correct, consider modifying the hypothesis

• Should the experiment be modified?

• Should additional data be collected?

• Be prepared to create a hypothesis that was not expected

Example Example -- The Journeys of ColumbusThe Journeys of Columbus

Formulating a Problem: An Alternate Trade Route to the Orient

Hypothesis: The world is a sphere and that by sailing West one could reach the East and establish a new trade route for Spain and Europe.

Objectives: To sail West and plot a new route; to compare the new route to old routes; to collect goods from the Far East andreturn to Spain

Challenge of the Hypothesis: The East was not reached; the New World was “discovered”; goods were returned to Spain

ModelsModels

• Geometric

• Kinematic

• Dynamic (Mechanical)

Geometric ModelsGeometric Models

• Interpretation of geologic structures in 2-D and 3-D

• Useful data - geological mapping, geophysical surveys

• Common geometric models - maps, cross-sections, block diagrams, movies

Geologic cross-section, Kolob Canyons, Zion National Park

Kinematic ModelsKinematic Models

Kinematic cross-section of faulting

• Specific history of motion from the undeformed state to the deformed state

• No consideration of physical properties or driving forces of motion

• Plate Tectonics is a good example of a kinematic model

Dynamic (Mechanical) ModelsDynamic (Mechanical) Models

• Deformation is a function of the physical conditions and mechanical properties of the model

Numerical model of the interaction between a mantle plume and spreading ridge

Group exerciseGroup exercise

In groups of four, develop a hypothesis related to some aspect of earth science.

• Identify the problem

• Ask the key question

• Research and evaluate

• Develop a multiple working hypothesis

• Challenge the hypothesis

• Modify the hypothesis or experiment

If time permits, we will share some of the hypotheses with the class.

The interdisciplinary nature of modern Earth ScienceThe interdisciplinary nature of modern Earth Science

As a research geologist, I use many types of data

Making maps: traditional mapping, airborne and space photography, digital elevation data (USGS, SRTM) for shaded relief, slope and curvature maps, GPS (for locating contacts), INSAR data for mapping ground movement

For making cross sections: Traditional map data, measurements in the field, GPS (regional velocities), seismic reflection profiles, oil and geotechnical boreholes (bucket auger + CPT), earthquake seismicity, trench excavations

For making models, I use mostly computer programs, 3D visualization, Coulomb (stress calculations), Trishear and Forced Fold (determining fault geometries from fold shapes). My students also use Matlab, ArcGIS, and code for processing images and managing diverse databases.

New Madrid: ShortNew Madrid: Short--lived lived intraplate intraplate folding in a folding in a dextral restraining benddextral restraining bendBig earthquakes (Mw ~7.4)Big earthquakes (Mw ~7.4)22--3m slip @600 yr interval3m slip @600 yr intervalAD 1811, 1450, 900, 300AD 1811, 1450, 900, 300Little total uplift (50 m)Little total uplift (50 m)

Aftershocks from 1811Aftershocks from 1811Miss. River FloodplainMiss. River FloodplainLoess UplandsLoess Uplands

ReelfootReelfoot

Cotto

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ault

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ltFloodplainFloodplain LakeLake

•• Surface Surface deformation deformation occurs mostly by occurs mostly by subtle foldingsubtle folding

•• Most uplift Most uplift occurs above occurs above thrustthrust

•• Only portion of Only portion of fold preservedfold preserved

fold scarp fold scarp

UplandsUplands

New Madrid Shaded ReliefNew Madrid Shaded Relief

•• Topographic relief in NMSZ is Topographic relief in NMSZ is subtle (<5 subtle (<5 --8 m on floodplain)8 m on floodplain)

Topo Topo ProfileProfile UpliftUplift

LakeLakeRiverRiver

BasinBasin

Reelfoot Reelfoot scarp:scarp:Forelimb of foldForelimb of fold

•• 9m uplift in 2300 yrs (slip rate: 4.09m uplift in 2300 yrs (slip rate: 4.0++1.0 mm/yr)1.0 mm/yr)•• 44--5 m of slip per event (~every 600 years)5 m of slip per event (~every 600 years)•• 3 surface fold scarps suggests strain is distributed 3 surface fold scarps suggests strain is distributed

unevenly in forelimb, unevenly in forelimb, records heterogeneous shearrecords heterogeneous shear•• Secondary extensional strain, no flexural slip faultsSecondary extensional strain, no flexural slip faults•• No longNo long--term record of growth strataterm record of growth strata•• LongerLonger--term variation in slip rate is undefinedterm variation in slip rate is undefined•• Don’t know why it turns on @ 15 kaDon’t know why it turns on @ 15 ka

Trench Log across Trench Log across Reelfoot Reelfoot ScarpScarp

HighHigh--resolution seismicresolution seismic(Sexton & Jones, 1986)(Sexton & Jones, 1986)

•• fault propagation foldfault propagation fold•• reflectors flatten upward reflectors flatten upward •• fault offset at 0.6secfault offset at 0.6sec•• no growth stratano growth strata

•• Undertake structural Undertake structural analysis to determineanalysis to determinedip of fault (i.e. to dip of fault (i.e. to determine slip rate)determine slip rate)

•• restores stratarestores strata•• defines fault dip (75defines fault dip (75oo))•• estimates propagation estimates propagation

of fault tip relative toof fault tip relative tofault slip (P:S ~ 9.0)fault slip (P:S ~ 9.0)

•• determines thatdetermines thatfault is reactivatedfault is reactivated

Simple Simple Trishear Trishear ModelModel

Downtown OsakaDowntown Osaka Now lets move to Japan…Now lets move to Japan…

Uemachi Uemachi Upland/FoldUpland/Fold

Kuwana Kuwana AnticlineAnticline

3D image of uppermost surfaces folded by 3D image of uppermost surfaces folded by Uemachi Uemachi FlexureFlexure

Base MaBase Ma--1313

Top MaTop Ma--1313

Top MaTop Ma--1212

Base MaBase Ma--1212

Note progressive increase in Note progressive increase in relief across forelimbrelief across forelimb

Well data from GeoWell data from Geo--Research Institute, OsakaResearch Institute, Osaka

Uemachi Uemachi SS--wave profilewave profile

Note resolution of data (some reflectors at 1 m spacing)Note resolution of data (some reflectors at 1 m spacing)Reflectors Reflectors steepen steepen downwarddownwardAngular unconformity from Holocene sea levelAngular unconformity from Holocene sea level highstandhighstand

0000

--1010

--2020

--3030

--4040

--5050

--6060

0000

--1010

--2020

--3030

--4040

--5050

--6060

Depth inDepth inmetersmeters

UemachiUemachi SS--wave profile plus boringswave profile plus borings

Only negative Only negative impedenceimpedence shownshown

UemachiUemachi SS--wave profile + line tracingwave profile + line tracing

Note upwardly narrowing Note upwardly narrowing trisheartrishear envelopeenvelope

UemachiUemachi line tracing + interpretationline tracing + interpretation

Note flexural slip faults that terminate as parasitic folds beneNote flexural slip faults that terminate as parasitic folds beneath unconformityath unconformitySome of this strain may postdate deposition of younger strataSome of this strain may postdate deposition of younger strata

Backfilling occurs above flexural slip foldsBackfilling occurs above flexural slip folds

Osaka BayOsaka Bay

Osaka Bay FlexureOsaka Bay Flexure

Dip profile of forelimb of Osaka Bay FPF/blind thrustDip profile of forelimb of Osaka Bay FPF/blind thrust

Most of reflectors are growth strataMost of reflectors are growth strata1.51.5--2.0 km of sediment fill in the last 1800 ka2.0 km of sediment fill in the last 1800 kaNote homogeneous shear in forelimbNote homogeneous shear in forelimb

Best fit Best fit trisheartrishear solution yields: steep (74 deg) thrust, 12km upward solution yields: steep (74 deg) thrust, 12km upward propagation (Fault tip from 15propagation (Fault tip from 15-->3km) 10 deg apical angle>3km) 10 deg apical angle

Dip profile of forelimb of Osaka Bay FPF/blind thrustDip profile of forelimb of Osaka Bay FPF/blind thrust