Magnitude 9! How We Learned That the Largest Earthquakes on Earth Happen in the Pacific Northwest

John J. Clague SFU Centre for Natural Hazard Research

What is an earthquake?

Prince 1946 Prince 2001 Rupert Vancouver Island Rupert Nisqually, Washington earthquake Shake maps earthquake magnitude 7.3 (Mercali intensity) magnitude 6.9 Campbell River: 75% of chimneys General alarm. collapse VII Difficult to stand. Damage to buildings. >$2 billion Lions Gate dollars in Bridge sways Courtenay: Felt by everyone. damage Post Office VI Difficult to walk. wall collapses Objects fall. Vancouver Vancouver Felt outdoors, Port Alberni: Victoria V Victoria Hundreds of Buildings sway. houses lose Seattle Seattle chimneys. Water Felt by most mains break. buildings IV people indoors. Power out for sway 10 days. Portland Portland

0 km 300 0 km 300

fig27.cdr How did we learn that giant earthquakes occur in the Pacific Northwest?

A 50-year odyssey marked by

spreading transform ridge earthquake ("teeth" on zone overriding volcanoes zone plate)

Eurasia Plate North America Plate Japan g o f F i n i r R e

Pacific Plate

South America Plate Nazca Plate Indo-Australia Plate

New Zealand

spreading Andes Pacific ridge volcanoes Ocean

Nazca Plate South America Pacific Plate Plate mantle subduction zone advances in scientificfig3.cdr knowledge and technology

Early 1960s – The revolution in earth sciences

spreading transform ridge fault earthquake subduction ("teeth" on zone overriding volcanoes zone plate)

Eurasia Plate North America Plate Japan g o f F i n i r R e

Pacific Plate

South America Plate Nazca Plate Indo-Australia Plate

New Zealand

spreading Andes Pacific ridge volcanoes Ocean

Nazca Plate South America Pacific Plate Plate mantle subduction zone

fig3.cdr

1963 - Drummond Mathewes and his PhD student Frederick Vine document magnetic striping on the seafloor

Earth’s lithospheric plates

spreading transform ridge fault earthquake subduction ("teeth" on zone overriding volcanoes zone plate)

Eurasia Plate North America Plate Japan g o f F i n i r R e

Pacific Plate

South America Plate Nazca Plate Indo-Australia Plate

New Zealand

spreading Andes Pacific ridge volcanoes Ocean

Nazca Plate South America Pacific Plate Plate mantle subduction zone

fig3.cdr 1970s – Recognition that there is a subduction zone off the coast of the Pacific Northwest …

spreading transform ridge fault earthquake subduction ("teeth" on zone overriding volcanoes zone plate)

Eurasia Plate North America Plate Japan g o f F i n i r R e

Pacific Plate

South America Plate Nazca Plate Indo-Australia Plate

New Zealand

spreading Andes Pacific ridge volcanoes Ocean

Nazca Plate South America Pacific Plate Plate mantle subduction zone

fig3.cdr But is there continuous slip or stick-slip at the boundary between the two plates? 1984 – Heaton and Kanamori ‘rock the boat’ Epicentre of 1964 earthquake

0 m Anchorage -1 m The story from

0 m other giant -2 m +1 m +2 m earthquakes

+6 m +3 m

region of uplift 0 100

region of subsidence km

Alaska Yukon N.W.T.

B.C.

Pacific Ocean George Plafker

fig30.cdr Between Uplift earthquakes Vancouver Island Pacific Ocean Strait of Georgia crust shortens (compression) locked

During Uplift earthquakes Subsidence

crust pulls apart rupture (extension)

fig51b.cdr 1987 - The “aha” moment

Brian Atwater

Niawiakum River, WA Copalis River, WA tidal marsh

AD 1700

~AD 700 ~AD 300

~600 BC

~1000 BC

Niawiakum River, WA

fig60.cdr Recurrence Vikings Columbus Great Pyramids Greek State The Roman Empire settle NE "discovers" of Egypt built flourishes America America

Great earthquakes in the Pacific Northwest

2000 BC 1000 BC 1 AD 1000 AD Today Time 1990s - Support from the geophysicists Natural Resources Canada Roy Hyndman

Kelin Wang Between 1990s to present – Uplift earthquakes Vancouver Island Pacific Ocean Strait of Georgia Documentingcrust shortens the expected secondary effects (compression) locked

During Uplift earthquakes Subsidence crust pulls apart rupture (extension)

fig51b.cdr PhiPhi Island, Thailand Tofino, BC Chronologies

Twenty great earthquakes in the past 10,000 years The orphan They occur in clusters Are we in a cluster or in the interval between two clusters? The future –

• Refined map of the locked zone

• Further refinements in the earthquake

chronology

• Tackling the issue of segmentation

• Search for precursor signals The future –

• Refined map of the locked zone

• Further refinements in the earthquake

chronology

• Tackling the issue of segmentation

• Search for precursor signals Clague et al., 2006 "silent slip period of event" slow buildup of strain

short period of intense period tremor of no activity tremors

Herb Dragert Garry Rogers

fig54.cdr Natural Resources Canada Herb Dragert, National Resources Canada The End