Simulating big earthquakes Accessing the inaccessible with models

Subduction zone earthquakes Two stories of deformation and stress Pacific Ocean EurasiaNorth America 1: 1995 M8 Jalisco, Mexico quake 2: 2004 M9 Sumatra-Andaman quake

North America Pacific Ocean North American Plate Mexico Middle America Trench Pacific Ocean Middle America Trench kilometers N 4 cm/yr Rivera Plate 1. The M8 Jalisco Earthquake: A natural laboratory for stress-triggering M8 Jalisco Quake

Subduction zone Converging tectonic plates North American Plate Mexico Middle America Trench Pacific Ocean Mexico 4 cm/yr North American Plate Middle America Trench kilometers N Pacific Ocean North American Plate Mexico Rivera Plate Rivera Plate North American Plate oceanic crust continental crust M8 Jalisco Quake

Earthquakes Release of built-up tectonic stress Rivera Plate North American Plate cross-section oceanic crust continental crust M8 Jalisco Quake

Study site 1995 Jalisco earthquake Rivera Plate North American Plate Mexico Middle America Trench Pacific Ocean Middle America Trench kilometers N 1995 Feb, GPS sites installed Oct 9, M=8 Dec 11, M=6 GPS site 0.5 m 4 cm/yr North America Pacific Ocean M8 Jalisco Quake

Observations Earthquakes close together in both space & time October 9, M=8 December 11, M= kilometers 63 days * earthquakes linked together rupture plane M8 Jalisco Quake

Storage and release of elastic energy Tectonic stresses load fault Rocks store elastic energy Frictional resistance of fault is overcome Stress-triggering 101: The interaction of earthquakes M8 Jalisco Quake

Storage and release of elastic energy Tectonic stresses load fault Rocks store elastic energy Frictional resistance of fault is overcome Stress-triggering 101: The interaction of earthquakes M8 Jalisco Quake

Storage and release of elastic energy Tectonic stresses load fault Rocks store elastic energy Frictional resistance of fault is overcome Stress-triggering 101: The interaction of earthquakes M8 Jalisco Quake

tectonic stress normal stress friction Storage and release of elastic energy Tectonic stresses load fault Rocks store elastic energy Frictional resistance of fault is overcome Stress-triggering 101: The interaction of earthquakes M8 Jalisco Quake

tectonic stress normal stress friction tectonic stress (winch) normal stress (gravity) friction (sandpaper) Storage and release of elastic energy Tectonic stresses load fault Rocks store elastic energy Frictional resistance of fault is overcome Stress-triggering 101: The interaction of earthquakes M8 Jalisco Quake

Earthquake coupling Stress release from loads other faults Quake 1 may trigger Quake 2 fault 1 quake 1 fault 2 quake 2 Stress-triggering 101: The interaction of earthquakes M8 Jalisco Quake

Earthquake coupling Stress release from an earthquake loads other faults Quake 1 may trigger Quake 2 1 stress transfer friction normal stress 2 tectonic stress normal stress Stress-triggering 101: The interaction of earthquakes M8 Jalisco Quake

1 stress transfer friction normal stress 2 tectonic stress normal stress tectonic stress (winch) normal stress (gravity) friction (sandpaper) normal stress (gravity) stress transfer (elastic material) 22 1 Stress-triggering 101: The interaction of earthquakes Earthquake coupling Stress release from an earthquake loads other faults Quake 1 may trigger Quake 2 M8 Jalisco Quake

What about the time lag? A good model must also account for the 63-day lag October 9, M=8 December 11, M= kilometers 63 days * earthquakes linked together rupture plane lag M8 Jalisco Quake

Hypothesis October 9, M= kilometers fault stress (from M=8 quake) pore pressure along fault slowly increases after M=8 quake pore pressure (along fault of M=6 quake) triggered M=6 quake +  pore pressure: pressure of water in the pores of the rock. definition M8 Jalisco Quake

Poroelastic mechanics Physical interaction of rock and pore water saturated rock rock matrix fluid-filled pore 0 –+ pore pressure  tension 0 –+ pore pressure  compression M8 Jalisco Quake

Earthquake mechanics The meaning of and pore pressure  tension 0 – + pore pressure  tension 0 – + compression 0 – + pore pressure  compression 0 – + pore pressure   fault M8 Jalisco Quake

Rivera plateNorth American plate   M = 8 ( t = 0 ) M = 6 ( t = 63 days ) tension compression cross-section of subduction zone pore pressure near M=6 fault 0 –+ t = 63 days fluid flow 0 –+ t = 0 + Conceptual model Earthquake  released stress and pore pressure M8 Jalisco Quake

* Coulomb stress along fault can change due to fluid flow  changing pore pressure Coulomb stress tendency for slip to occur along a fault definition 0 –+ shear stress normal stress pore pressure fault pore pressure shear stress normal stress friction Fault stability: Coulomb stress Combination of stress, pore pressure, and friction M8 Jalisco Quake

Fault Stability: Coulomb Stress Experiment apparatus 0 –+ shear stress normal stress water pressure fault shear stress normal stress water pressure fault M8 Jalisco Quake

Fault Stability: Coulomb Stress Experiment apparatus normal stress fault water pressure = 0 shear stress = 0 normal stress  0 initial conditions M8 Jalisco Quake

Fault Stability: Experiment Earthquake changes Coulomb stress earthquake shear stress normal stress fault M8 Jalisco Quake

Fault Stability: Experiment Pore pressure changes  Coulomb stress changes earthquake shear stress normal stress fault water pressure excess water pressure induction device M8 Jalisco Quake

Fault Stability: Experiment Pore pressure changes  Coulomb stress changes shear stress normal stress fault water pressure excess water pressure induction device M8 Jalisco Quake

- GPS station 1800 km 1300 km 250 km 220 km oceanic crust continental crust mantle FEM: numerical model; predicts deformation, stress, and pore pressure due to earthquakes. definition Method: Construct deformation models Finite Element Model (FEM) M8 Jalisco Quake

M=6 epicenter ( pore pressure initially drops after M8 quake ) 1800 km 1300 km oceanic crust continental crust pore pressure (kPa) North days after M=8 earthquake: Predicted pore pressure Initial conditions following M8 earthquake M8 Jalisco Quake

1800 km 1300 km oceanic crust continental crust pore pressure (kPa) North days after M=8 earthquake: Predicted pore pressure Gradual recovery to pre-earthquake equilibrium M=6 epicenter ( pore pressure slowly increases after M8 quake ) M8 Jalisco Quake

 The M=8 earthquake triggered the M=6 earthquake, fluid flow accounts for the delay the M=6 earthquake was a predictable event ! stress (from M=8 quake) pore pressure (along fault of M=6 quake) triggered M=6 quake +  Conclusions Recall the hypothesis… M8 Jalisco Quake

stress (MPa) - GPS station 220 km years after M=8 earthquake The Project Continues Predicting deformation & stress evolution brittle upper crust (stress accumulates) ductile mantle (stresses relax) M8 Jalisco Quake

Earthquake coupling Stress release loads mantle Flow relaxes stresses in mantle (silly putty) and transfers stress to fault 1 1 stress transfer friction normal stress 2 tectonic stress normal stress Stress-triggering: Viscoelastic relaxation viscous silly putty (slowly flows & relaxes stress) M8 Jalisco Quake

M9 earthquake tsunami Indian Ocean Sumatra India Australia 2. Applying the lessons learned 2004 M9 Sumatra-Andaman earthquake & tsunami M9 Sumatra-Andaman Quake

Indo-Australian Plate Eurasian Plate 6 cm/yr 9.2 Rupture & deformation 2004 M9 Sumatra-Andaman earthquake & tsunami Dec M9 Sumatra-Andaman Quake

Indo-Australian Plate Eurasian Plate 6 cm/yr 9.2 Sumatra-Andaman FEM 1) Simulate poroelastic stress-triggering 6 cm/yr Mar Dec M9 Sumatra-Andaman Quake

Are the aftershocks predictable in space and time?  not yet, but…we are working on it! Coupling the 2004 & 2005 quakes What if models in place prior to these events? M9 Sumatra-Andaman Quake

up down Indo-Australian Plate Eurasian Plate 6 cm/yr 9.2 Dec Sumatra-Andaman FEM 2) Simulate seafloor deformation  tsunamigenesis M9 Sumatra-Andaman Quake

Predicting seafloor deformation Changes overlying water column seafloor ocean surface cross-section water column Indo-Aust Plate Eurasian Plate fault M9 Sumatra-Andaman Quake

Predicting seafloor deformation Changes overlying water column seafloor ocean surface cross-section water column Indo-Aust Plate Eurasian Plate fault M9 Sumatra-Andaman Quake

seafloor cross-section wave propagation earthquake deformation India and Sri Lanka Sumatra & Thailand Predicting seafloor deformation Drives tsunami propagation models M9 Sumatra-Andaman Quake

seafloor cross-section wave propagation Sumatra & Thailand India and Sri Lanka M9 Sumatra-Andaman Quake Predicting seafloor deformation Drives tsunami propagation models

seafloor cross-section earthquake deformation cross-section ocean surface wave propagation: velocity is a function of depth slow fastfast slow M9 Sumatra-Andaman Quake Predicting seafloor deformation Drives tsunami propagation models  run-up

seafloor cross-section earthquake deformation cross-section wave propagation: velocity is a function of depth slow fastfast slow M9 Sumatra-Andaman Quake Predicting seafloor deformation Drives tsunami propagation models  run-up

In progress: Virtual Sumatra-Andaman subduction zone M9 Sumatra-Andaman Quake

In progress: Virtual Sumatra-Andaman subduction zone

M9 Sumatra-Andaman Quake In progress: Virtual Sumatra-Andaman subduction zone seafloor deformation

M9 Sumatra-Andaman Quake In progress: Virtual Sumatra-Andaman subduction zone seafloor deformation Imagine the possibilities… deformation predictions (tsunami sources) stress evolution predictions  ultimately, earthquake predictions