The 2015 Gorkha (Nepal) earthquake:unfinished business

Large earthquakes in the Himalaya and India

James Jackson, Bullard Laboratories, University of Cambridge

8 metres

1857 California: San Andreas Fault

Earthquakes happen on faults

The Earthquake Mechanism

epicentre

300 million years ago

U.S. Geological Survey

Contrasts within the continents (old vs. young)

Earthquake depth distributions

Moho(base ofthe crust)

Earthquakes either in upper crust or in whole crust…but not significantly in continental mantle

Maggi et al 2000

Teleseismic depths:well-determinedfrom P and SH body-wavemodelling

T cutoff ~350oC

Mantle has earthquakes if colder than 600oC

T. Craig et al, GJI, 2014

CRUST

CRUST

MOR

CRUST:

ISENTROPIC INTERIOR:Tp = 1315oC

MANTLEconstantheat flux9.8 mw/m2

surface heat flux 58.6 mW/m2

Moho T = ~600 oC

‘LITHOSPHERE’thickness= 242 km

50 km

SIBERIANSHIELD

earthquakes

Moho

McKenzie et al, EPSL, 2005

…needs DRY lower crust(granulite composition)

Moho

Depth to baselithospherekm

9000 paths

Priestley & McKenzie, EPSL, 2006

resolution: X-Y ~150-200 kmZ ~ 30 km

Africa rifting

Archean

TeleseismicCraig et al, GJI, 2011

Lithosphere thicknessGeology

black: Proterozoicor older

grey: Pan-African

from local microearthquake

surveys

Craig et al, GJI, 2011

North South

Craig et al, GJI, 2011

26

30

15

40

40

Central Asia

rifting

Sloan et al, GJI, 2011

Siberia

Mongolia

India

forelands

Jackson, GSA Today, 2002; Sloan et al GJI, 2011

Moho depthEarthquake depth

Alps

forelands

Kastrup, Deichmann et al, JGR, 2004

Deichmann, PEPI, 1992

“...temperatures in the lower crustal seismic zone are well above 450oC.”

Monsalve et al, JGR, 2006

CRUST

MANTLE

Himalaya and south Tibet

Moho ~500oC

600oC

57

Priestley et al 2008 Monsalve et al 2006

CRUST

MANTLE

Earthquakes M>5.5 and deeper than 60 km 1965-2006

Copley & McKenzie, GJI, 2007topographic front

India Kazakhstan

Sloan et al, GJI, 2011

The lower continental crust can have earthquakes up to 600oC ….. usually dry granulite composition associated with shields

Usually only the upper continental crust has earthquakes (up to about 350oC)

Strong lower crust supports mountain fronts, not the mantle

What’s special about ancient shields?

Implications

…earthquake size depends on fault length and area

Copley et al, JGR, 2011

INDIA 18972001

Vicky Stevens

The 2015 Gorkha (Nepal) earthquake

Tibet

India

2005 Muzaffrabad 2008 Sichuan

2015 Nepal

TIBET

NEPAL

J P Avouac, Caltech

Moho

locked

1934

TIBET

INDIA

Bollinger et al., 2014, JGR, Fig8; also Sapkota et al, 2013, Nature Geoscience

2015

2015

Before the earthquake…. monitoring with GPS

GPS in Nepal

Tibet

India

Nepal

velocities relative to India

J-P Avouac

GPS velocities relative to India

J-P Avouac

locked fault width 110 km

creeping zone~17 mm/yr

TIBETINDIA

J-P Avouac

Kathmandu

Earthquakes 1995-1999

J-P Avouac

up to 3500m3000-5000m>5000m

Larger earthquakes (M>5.5) 1965-2005

Base of the locked zone follows the 3500m contour

The Mw 7.8 GorkhaEarthquake, Nepal

Preliminary Observations Jean-Philippe Avouac

Bullard LaboratoriesUniversity of Cambridge

CollaboratorsVicky StevensKristel ChanardThomas AderMarion ThomasPierre BettinelliLaurent BollingerFrancois AyoubRodolphe CattinJerome Lave

National Seismic Center (DMG, Nepal):Madhab PandeySudhir RajaureSom Sapkota

Institute for Tibet Research (China)Jing Liu

IISER Kolkata (India) Supriyo Mitra

John GaleztkaJeff GenrichMireille FlouzatDiego MelgarShengji WeiJean-Paul AmpueroLingsen MengTeng Wang

+ John Elliott (Oxford)NOT James JacksonKeith Priestley (Cambridge)

J P Avouac John Elliott

John Elliott

Mw 7.8 25th April 2015: aftershocks in first two weeks John Elliott

Mw 7.8 25TH April 2015 Mw 7.3 12TH May 2015

25 April

12 May

John Elliott

Displacement GPS seismogram at KKN4north of Kathmandu

Processed by SOPAC(5 samples/second)

J-P Avouac

AFTERMainshock

(M 7.8) of 25 April

BEFOREAftershock

(M7.3)of 12 May

Aftershocks M>4

J-P Avouac

AFTERAftershock

(M7.3)of 12 May

Aftershocks M>4

Diego Melgar

Interseismic coupling from Ader et al (2012)Yellow patch, slip >1m, joint inversion of teleseismicwaveforms an SAR amplitude offsets.

J P Avouac

Elliott et al, Nature Geoscience, in press

Pass 2: post earthquake

phase (distance) shiftdue to ground motion

780

kmRadar interferometry

= 5.6 cm

Pass 1: pre earthquake

Tim Wright

DOWN

UP

John Elliott

Changes in line-of-sight distance to satellite(each fringe = 10cm)

90 km

John Elliott

4.5m

0m

Kathmandu

faultslip

90 km

John Elliott

Galetzka et al, Science, 2015

Static stress drop after the Gorkha mainshock.Aftershocks M>4Aftershocks M>6

John Elliott

??

Aftershocks M>4 recorded until 15 September 2015

J-P Avouac, Supriyo Mitra, Keith Priestley

3 33 moreTo west

Post-mainshock GPS displacements 25 April to 1 July

J-P Avouac

Kathmandu

Post-mainshock GPS displacements 25 April to 15 September

J-P Avouac

50 mm

(landslide)

Kathmandu

Kathmandu valley

… a former lake basin

Kathmandu pre-earthquake

Kathmandu pre-earthquake

Kathmandupre-earthquake

Kathmandupre-earthquake

Bedrock Kathmandu basinseconds

Tomijung village

Majgaun (upper village)

Thulo Sabro Roger Bilham

Roger BilhamGogne

John Elliott

??It’s not over yet

Conclusions (Gorkha EQ)

• Blind rupture, unzipped down dip edge ofLocked Main Himalayan Thrust

• Repetition of similar past events (1833)recurring every about 100yrs

• Clear pulse like rupture with 5 6s rise time,3km/s propagation.

• Put Kathmandu basin in resonance at 4 5s, butnot much shaking at higher frequencies(16%g).

What can be done?

Amod Dixit

Roger BilhamBarpak reconstruction

NSET: National Society for Earthquake Technology

Retrofitted school, Lalitpur

Retrofitted school, Lalitpur

NSET

Women’s group, Kirtipur

Women’s group, Kirtipur

Earthquakes 1962-2003

The earthquake belt of the Mediterranean – Middle East - Asia

East-west trade routes: the ‘Silk Road’

Trade routes follow the geological structures:the edges of deserts, plateaus and mountains

are all formed by earthquake faulting

>10,000 dead>100,000 dead

Earthquakes that killed more than 10,000 people: 1000-2008 AD

36 of them in the last 100 years120 in total (worldwide):

1887, 1889, 1911destroyed in 855, 958, 1137, 1830

Bishkek

faults

Also: Ashkhabad (1948), Tashkent (1966), Wenchuan (2008)....

1885

Tabriz, Iran

Daily problems of:congestion, pollution, air quality, water supply (and health, poverty) etc.…

Complex Physical SystemEarthquakes without frontiers

At risk population density

earthquakes1964 2007

M>5

1900 2000M>6

cities>500,000

inhabitants

people per 5km2 inearthquake zones

ItalyGreeceTurkey

IranArmeniaAzerbaijan

NepalIndiaPakistan

China

KazakhstanKyrgyzstanUzbekistanTurkmenistan

Earthquakes without frontiers

Bam 2003

Vision

Better knowledge of the earthquakehazards and their context

Find effective pathwaysto improved resilience

Training and exchange of knowledge

‘For years I fought a losing battle to keep away from involvement with the notion of earthquake prediction. The press and public will go toward the suggestion of prediction like hogs to the trough. Meanwhile, other objects of investigation are neglected or distorted; and aid is given to the people who would like to forget the fact that for public safety we don’t need prediction –-that earthquake risk could be removed, almost completely, by proper building construction and regulation.’ (Charles Richter, retirement speech 1970)

Earthquake prediction is NOT the answer