SCEC Earthquake Gates Workshop Central Death Valley Focus Area

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1 SCEC Earthquake Gates Workshop Central Death Valley Focus Area

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3 Fault Gates: Rheology, fault geometry, stress history or directionality? How do we recognize or suspect a fault gate? Paleoseismic or historic rupture history and behavior 3D (surface and subsurface) fault geometry and maturity Long term geomorphic evidence Mechanical models Why do we think Central Death Valley has fault gates? Clear geomorphic evidence for intermediate to long term shutting off and on of faults across releasing bends. Surface fault geometry

4 Timescales matter! For SCEC, short timescales (at earthquake recurrence) probably matter the most in terms of hazard. But these studies should look at as long a time period as possible. Mega, super, giant trenches? Or boreholes and very high resolution seismic at sites with high resolution seismic + high frequency stratigraphy. Intermediate scales (tens s of Ka) offer another opportunity to assess fault interactions less related to stress transfer and more related to toggling and fault strength + fluids.

5 What evidence exists for turning off and on of fault segments at intermediate to long term timescales? Exhumed early Pliocene strata in an elongate block the Artist s Drive area of central Death Valley. Little evidence for recent offset at frontal edge of block. Clear evidence from lidar of active slip behind the block (continuation of fault further north). Well exposed sequence of Early Pliocene sediments in Copper Basin a record of subsidence in a paleo-releasing bend.

6 Details of fault stepovers in DV Red line marks the most likely point of a fault break in the next earthquake in Death Valley

7 Fault stepovers in DV Dashed red lines denote inactive parts of older rangefront fault system. Why did these turn off?

8 Rangefront north of Artist s Palette stepover has obvious recent displacement. Stepover itself (normal fault) is highly embayed with little evidence for recent slip. Same for inactive part of range-front further south.

9 Exhumed early Pliocene strata in now inactive releasing bend at Artist s Palette

10 Fault stepovers in DV Dashed red lines to south defines trace of Copper Basin detachment. Bypassed by more recent slip now connected to Mormon Point stepover

11 Fault stepovers in DV Copper Basin Exhumed Pliocene section in Copper Basin Dashed red lines to south defines trace of Copper Basin detachment. Bypassed by more recent slip.

12 Mormon Point Stepover Mormon Point steopover records evidence for 3 to Earthquakes over the last 10,000 years. Earthquakes rupture across this easily Mormon Point Stepover

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14 Advantages of central Death Valley Well defined recent strain history from previous work, based on lidar Clear evidence for fault segments turning on and off. Disadvantages of central Death Valley Restrictions for excavations (National Park) Not Southern California Subsurface fault geometry poorly constrained.

15 What hazard questions does DV address? How and why do previously hard linked strike slip fault segments turn on and off? Not a lot of hazard in Death Valley except NPS infrastructure What fundamental problems in earthquake science does DV address? What drives fault switching? Rheology, fault geometry, stress history or directionality? Why does switching occur at longer timescales? Fault organization + fault strength???

16 What are the goals, data needs, and modeling investigations of proposed EGA? How and why do previously hard linked strike slip fault segments turn on and off? 3D fault geometry + physics-based numerical modeling Fault rock strength data

17 0 Since I have a room full of experts, here is some scary stuff to consider from Japan that pertains to this workshop. a. GS-8ME b. OD-B 1 km c. HD-3 d. HD-4 1 km 2 3

18 TDL plot Time-displacementlength. Trade width of fault for time. Fault grows to it s endpoint immediately (evidence for reactivation). Slip rates higher in center with time. Fault shuts off and on (twice) for periods of ~50 Ka (sidewalks on 3D diagram. This is the scary part. Throws uncertainty into what we all do. Question is behavior to 10Ka timescale when fault slows down or speeds up.