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Using this approach we have integrated all of the tidal and leveling records from coastal Oregon to determine the 3d uplift pattern along the coast. Benchmark uplift rates projected contour-perpendicular. Topography. Updip Deformation Sources. Interseismic deformation due to plate convergence.

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Using this approach we have integrated all of the tidal and leveling records from coastal Oregon to determine the 3d uplift pattern along the coast.

Benchmark uplift rates projected contour-perpendicular

Topography


Updip Deformation Sources leveling records from coastal Oregon to determine the 3d uplift pattern along the coast.

  • Interseismic deformation due to plate convergence

Trench

Central OR Coast


Both NOAA’s calculated absolute sea level trend estimates and the more precise difference between the two sites suggest that North Spit subsides relative to Crescent City at about ~5.4 mm/yr. Given eustatic sea level rise of ~2.3 mm/yr for 1977 to 2010, Crescent City rises, absolutely, at ~3 mm/yr and North Spit sinks at about ~2.5 mm/yr.


Updip Deformation Sources and the more precise difference between the two sites suggest that North Spit subsides relative to Crescent City at about ~5.4 mm/yr. Given eustatic sea level rise of ~2.3 mm/yr for 1977 to 2010, Crescent City rises, absolutely, at ~3 mm/yr and North Spit sinks at about ~2.5 mm/yr.

  • Interseismic deformation due to plate convergence

Possibly?

Crescent City

North Spit

Trench

Trench

Central OR Coast


Preliminary reanalysis of the HW101 line from the Strait of Juan de Fuca (BM) to Aberdeen (Ab) supports the hypothesis that at least part of the westernmost coast is subsiding and there are very large gradients in uplift. However, this is based on a short repeat time in the releveling and is a very long distance unsupported by tide gauges to assess cumulative error in the leveling.

Tidal records from La Push (LP) and Point Grenville (PG) will confirm (or deny!) this hypothesis, and IF 2nd order leveling lines could be repeated between them and HW101 these tide gauges could stabilize the coast.


Earthquake geology indicates a megaquake occurs every 700 years
Earthquake geology indicates a megaquake occurs every ~700 years

Nanayama, et al., Nature (2003)

Sawai, et al., Nature (2003)


1857 Earthquake Surface Slip years

> 420 offset features identified (previous work identified ~150 offsets)

Courtesy of

O. Zielke


For the Carrizo Plain and Big Bend region we see repeated “characteristic” offsets of about five m.

Courtesy of

O. Zielke


Much of the deformation at the Wrightwood site is distributed across complicated small faults and folds that, in the few places we have deeply exposed them, root into low angle structures. To calculate the slip associated with these structures we have used a cross sectional area balancing approach often used to relate growth strata or erosional unconformities to detachments at depth.


Summary distributed across complicated small faults and folds that, in the few places we have deeply exposed them, root into low angle structures. To calculate the slip associated with these structures we have used a cross sectional area balancing approach often used to relate growth strata or erosional unconformities to detachments at depth.

of Wrightwood Upper Section’s ages and offsets. Note the huge uncertainties in slip. It is difficult to measure slip per event because the deformation zone is broad and complex. But if the zone was simple we could document few earthquakes due to deformation overprinting.

See Weldon et al., BSSA, 2002; GSA Today, 2004, for details


WW compared to new AMS dates at Pallett Creek distributed across complicated small faults and folds that, in the few places we have deeply exposed them, root into low angle structures. To calculate the slip associated with these structures we have used a cross sectional area balancing approach often used to relate growth strata or erosional unconformities to detachments at depth.

70% (10 of 14) correlate

Last two quakes that don’t correlate have good evidence to be southern events.

Paleoseismology, if done well is repeatable and gives us long interpretable records.

Cluster at Wrightwood is made of multiple northern and multiple southern events, so can’t just be overlap.


Historic distributed across complicated small faults and folds that, in the few places we have deeply exposed them, root into low angle structures. To calculate the slip associated with these structures we have used a cross sectional area balancing approach often used to relate growth strata or erosional unconformities to detachments at depth.

Period

Extra North

Bend events

Went

south

1857-like ?

Went

south

The data

Some interpretation


Summary distributed across complicated small faults and folds that, in the few places we have deeply exposed them, root into low angle structures. To calculate the slip associated with these structures we have used a cross sectional area balancing approach often used to relate growth strata or erosional unconformities to detachments at depth.

of Wrightwood Upper Section’s ages and offsets. Note the huge uncertainties in slip. It is difficult to measure slip per event because the deformation zone is broad and complex. But if the zone was simple we could document few earthquakes due to deformation overprinting.

See Weldon et al., BSSA, 2002; GSA Today, 2004, for details


Completeness distributed across complicated small faults and folds that, in the few places we have deeply exposed them, root into low angle structures. To calculate the slip associated with these structures we have used a cross sectional area balancing approach often used to relate growth strata or erosional unconformities to detachments at depth. – Constant sedimentation?

Are there gaps in the record?

Age Resolution – # of units per unit time?

Number of dated units?

Unit resolution – Thickness and distinctiveness of units.

Sharpness and planarity of contact surfaces?

Site characteristics – Narrow or broad zone of deformation?

Degree of Exposure – Number of fault crossing trenches?

Frequency of exposure of key layers? Ray’s Rule!

Evidence quality – Some sort of paleoseismic index? Kate’s?


  • Good sections include closed depressions that grow peat between frequent deposits of sediments, like this example from the Wrightwood paleoseismic site. Pieces of charcoal or other organic material can be used as well but detrital charcoal may be older than the unit that contains it.

Volume

Time


With a sedimentation rate of ~1 m/100 yrs, and individual clastic units representing on average 5-10 years, we can distinguish events that are likely separated by decades.

Here are two earthquakes separated by just 20-30 cms, and thus likely 20-30 years (as the C-14 shows in the next slide).


Completeness clastic units representing on average 5-10 years, we can distinguish events that are likely separated by decades. – Constant sedimentation?

Are there gaps in the record?

Age Resolution – # of units per unit time?

Number of dated units?

Unit resolution – Thickness and distinctiveness of units.

Sharpness and planarity of contact surfaces?

Site characteristics – Narrow or broad zone of deformation?

Degree of Exposure – Number of fault crossing trenches?

Frequency of exposure of key layers? Ray’s Rule!

Evidence quality – Some sort of paleoseismic index? Kate’s?


Catalogue of deformation clastic units representing on average 5-10 years, we can distinguish events that are likely separated by decades.


Depositional clastic units representing on average 5-10 years, we can distinguish events that are likely separated by decades. Order

Sum

Event Quality vs.

Stratigraphic Level

Sum of Quality

Sum of Observations


Event Quality vs. Stratigraphic Thickness clastic units representing on average 5-10 years, we can distinguish events that are likely separated by decades.

Debris Flow Thickness

Peat Thickness


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