The Deep Fault Drilling Project, Alpine Fault Getting Inside the Earthquake Machine

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1 The Deep Fault Drilling Project, Alpine Fault Getting Inside the Earthquake Machine John Townend Director, EQC Programme in Seismology and Fault Mechanics Head, School of Geography, Environment and Earth Sciences Victoria University of Wellington

2 Talk outline Recent, less recent, and future earthquakes in southern New Zealand How do big faults work? What do we think is important? Where does the Alpine Fault fit in? The Deep Fault Drilling Project (DFDP) Recent activities and results from DFDP-2 Summary and concluding thoughts

3 Talk outline Recent, less recent, and future earthquakes in southern New Zealand How do big faults work? What do we think is important? Where does the Alpine Fault fit in? The Deep Fault Drilling Project (DFDP) Recent activities and results from DFDP-2 Summary and concluding thoughts

4 30km NIWA 5 cm/yr New Zealand Plate Boundary 4 cm/yr 3.5 cm/yr

5 Prior to September 2010, few New Zealanders had experienced a large or disruptive earthquake

7 About 300 years and counting...

8 About 300 years and counting...

9 About 300 years and counting... Berryman et al., Science, 2012

10 About 300 years and counting... Based on this >6000 year record of ground-breaking earthquakes, the Alpine Fault is concluded to be late in its average interseismic cycle, with a ~28% likelihood of an M W 8 earthquake in the next 50 years Berryman et al., Science, 2012

11 There are little earthquakes around We use seismic waves produced by earthquakes to image the Alpine Fault tomographically, just as doctors image us with X-rays Feenstra et al., 2016

12 The fault is alive These bright spots represent fault zone guided waves, generated by earthquakes occurring on or very close to the deep Alpine Fault Eccles et al., 2015

13 The fault is alive We detect repeated small bursts of seismic energy known as lowfrequency earthquakes that show that the fault is slipping seismically Chamberlain et al., 2014

14 About 300 years and counting... Future Alpine Fault earthquakes will differ in many respects from what New Zealand has experienced since the 2010 Darfield earthquake: (1) the character of ground motions; (2) the extent of damage; and (3) the duration of aftershocks and other long-term effects

15 Talk outline Recent, less recent, and future earthquakes in southern New Zealand How do big faults work? What do we think is important? Where does the Alpine Fault fit in? The Deep Fault Drilling Project (DFDP) Recent activities and results from DFDP-2 Summary and concluding thoughts

16 What do we think matters? Earthquakes involve frictional sliding governed by the material properties of the rocks involved Rocks are saturated with fluids, whose pressures act to reduce friction Pressures are governed by the ease with which fluids can dissipate ( permeability ) Permeability is controlled by chemistry-, temperature- and stress-dependent processes Chemistry, temperature, and stress are controlled by tectonics and hydrology

17 What do we think matters? Earthquakes involve frictional sliding governed by the material properties of the rocks involved Fundamentally, the processes involved in Rocks are saturated with fluids, whose pressures act to reduce earthquake friction nucleation, propagation, radiation, and re-loading are in different ways Pressures intimately are governed associated by with the the ease chemical, with which fluids can dissipate ( permeability ) thermal, and hydraulic effects of fluid transport through the fault zone Permeability is controlled by chemistry-, temperature- and stress-dependent processes Chemistry, temperature, and stress are controlled by tectonics and hydrology

Gaunt Creek, near Whataroa, in February 2011 Stage 2

18 Deep Fault Drilling Project Preliminary workshop in 2007 ICDP workshop in 2009 Stage 1 completed at Gaunt Creek, near Whataroa, in February 2011 Stage 2 (targeting 1.3 km depth), Whataroa, Sept to Jan. 2015

19 Deep Fault Drilling Project How do large plate boundary faults evolve? How do they generate earthquakes? What controls the timing of Alpine Fault EQs? What are the temperatures, pressures, and stresses in the fault zone, late in the EQ cycle?

20 Deep Fault Drilling Project How do large plate boundary faults evolve? How do they generate earthquakes? What controls the timing of Alpine Fault EQs? What are the temperatures, pressures, and stresses in the fault zone, late in the EQ cycle? To sample ambient conditions, materials, and properties in situ, we need to drill and the Alpine Fault is the place to do this

21 Alpine Fault at Gaunt Creek

22 Alpine Fault at Gaunt Creek mylonites from 25 km crushed rock 15,000 yr old gravels Slide courtesy of Richard Norris, U. Otago

23 DFDP-1 technical goals Drill two boreholes to intersect the fault at ~150 m Retrieve core samples for detailed analysis Conduct geophysical logging of both holes Install permanent monitoring equipment

24 DFDP-1 technical goals Drill two boreholes to intersect the fault at ~150 m Retrieve core samples for detailed analysis Conduct geophysical logging of both holes Install permanent monitoring equipment

Sutherland et al., Geology, 2012 10 20 30 40 50 60 70 80 90 100 110 120 130 m Integrated Gaunt Creek cross-section A. Fault zone structure B.

Footwall cataclasite -16 2 k = 10 m 20-25 m DFDP-1A Gouge <2 m PSS <0.2-0.

25 Sutherland et al., Geology, m Integrated Gaunt Creek cross-section A. Fault zone structure B. Geology from outcrop DFDP-1B >20 m 150 m Fractured mylonite k = 10 m Cemented cataclasite k = 10 m Gravel 3 Fault core k = 10 m Footwall cataclasite k = 10 m m DFDP-1A Gouge <2 m PSS < m Topographic surface Water level Gravel k = 10 m Gravel 4 Fractured mylonite Cemented cataclasite Active river bed Water level inferred from DFDP-1B D. Regional cross-section Max SE 8 km 6 Min Sea level Alpine Fault 4 2 Gravel 1 C. Location South Island Australian New Zealand Plate DFDP AD earthquake 1620 AD 1430 AD DFDP-1 Alpine fault Gravel mm/yr Pacific Plate km Elevation (km) km NW N

26 Talk outline Recent, less recent, and future earthquakes in southern New Zealand How do big faults work? What do we think is important? Where does the Alpine Fault fit in? The Deep Fault Drilling Project (DFDP) Recent activities and results from DFDP-2 Summary and concluding thoughts

The goal of DFDP-2 is to determine the physical conditions at upper- and mid-crustal depths within a major active continental fault, the Alpine Fault, which is late in its earthquake cycle and which

27 The goal of DFDP-2 is to determine the physical conditions at upper- and mid-crustal depths within a major active continental fault, the Alpine Fault, which is late in its earthquake cycle and which can be monitored over coming decades. DFDP-2 is principally funded by: the International Continental Scientific Drilling Program (ICDP); the Royal Society of New Zealand; GNS Science; Victoria University of Wellington; the University of Otago; NZ Government (MBIE); and the UK Government (NERC).

28 Aerial view of drillsite 22 Oct Photo by Julian Thomson, GNS Science

29 Earthquake monitoring (plus nearby GeoNet and SAMBA sites)

30 Mud (and rock) samples 04 Oct Photo by Naoki Kato, Osaka University

31 Sample analysis 07 Oct Photo by Lucie Capova, Victoria University

nz) Gas chemistry measurements were made

32 Gas monitoring 04 Oct Photos by Lucie Capova, Victoria University Gas chemistry measurements were made automatically every few minutes throughout the drilling

33 Hot springs! 10 Oct Photos by Naoki Kato Osaka University

34 Wireline tools 30 Oct Photo by Julian Thomson, GNS Science

35 We measure everything

$fractures$

36 The rock is full of fractures

37 Borehole enlargement Low deep/shallow res. High sonic attenuation Structures in BHTV Analysis by Mai-Linh Doan and Cecile Massiot

38 Lots of locals came to see us Westland High School, December 2014

39 A technical failure in mid-december brought drilling to an abrupt and premature end, but not before we had successfully installed an optical fibre extending to 890 m for ongoing temperature and seismic measurements

40 Thermal profile It is much hotter than anticipated: the equilibrium geotherm is ~140 C/km (DFDP-1 gave 63 C/km) Fantastic! Documenting the fault s thermal structure is a key project objective related to many seismogenic questions But the temperatures pose technical and logistical problems

41 Key findings from DFDP-2 Very high temperatures (~140 C/km) High fluid pressures (~80 m head at 800 m) Low permeability

42 Key findings from DFDP-2 Very high temperatures (~140 C/km) What do these mean for the max. depth of EQ slip? High fluid pressures (~80 m head at 800 m) How do these influence EQ nucleation and rupture? Low permeability Is this what governs the time required to re-load?

43 University of Calgary EnviroVibe seismic source in action

44 Shots Receivers

45 Talk outline Recent, less recent, and future earthquakes in southern New Zealand How do big faults work? What do we think is important? Where does the Alpine Fault fit in? The Deep Fault Drilling Project (DFDP) Recent activities and results from DFDP-2 Summary and concluding thoughts

46 Possible ramifications At m scales, the fault zone is asymmetric in several senses: fracturing, geometry, compliance, permeability The SE (Pacific) side is more fractured than the NW (Australian) side but stiffer and less permeable Does the fault tend to rupture in one direction (NE)?

47 Possible ramifications At m scales, the fault zone is asymmetric in several senses: fracturing, geometry, compliance, permeability What would you do with a minute or two s warning that an earthquake was heading your way? The SE (Pacific) side is more fractured than the NW (Australian) side but stiffer and less permeable Does the fault tend to rupture in one direction (NE)?

48 Summary The central Alpine Fault is late in its typical earthquake cycle and an internationally significant target for understanding fault zone mechanics and the earthquake machine DFDP-2 did not reach its target depth of 1.3 km but has yielded exceptional petrophysical, hydrogeological, and thermal measurements Those data are currently the focus of analysis Planning for the next attempt is underway

49 Concluding thoughts Good science provides the context in which engineering and planning prepare society to cope with as-yet unexperienced events Media and communications networks let the public see and discuss what is happening ( data ) in great and immediate detail The responsibility of scientists to act as observers, interpreters and communicators, converting data into information and knowledge, is thus more important than ever

50 rupertsnztectonics.blogspot.co.nz Facebook: Deep Fault Drilling Project -2 Youtube: GNS Science

The Tectonic Setting of New Zealand

The Tectonic Setting of New Zealand we are here Subduction-driven tectonics The New Zealand continent Papua New Guinea Australia 3,000,000 sq km micro-continent back-arc basin trench volcanism faults accretionary