Choi, Jin-HyuckActive Tectonics Research Team, KIGAM

email: cjh9521@kigam.re.krwebsite: https://sites.google.com/site/jinhyuckchoi9521/

Active faults in Korea: recent research & current trends

Collaboration withKim, Y.-S. et al (Korean Active Fault Research Group)Lee, S.-R. et al (KIGAM project_17-3112)

CCOP-IUGS Task Group on Geohazards (TGG) Joint Seminar 30 Oct. 2018

MW 5.5 GJ eq. (Sep. 2016)

MW 5.4 PH eq. (Nov. 2017)

We are here

(updated from Roger Bilham, 2009)

Large earthquakes cause destructive disaster

1906 Mw 7.8 San Francisco eq. along the San Andreas fault

Earthquake rupture for all individual events

Earthquake ‘surface’ rupture for seismic events larger than MW 5.5

(Single-fault magnitude frequency relation) (Down-dip rupture width of earthquakes)

Surface records of large earthquakes

(Zielke & Arrowsmith, 2008)

Plate tectonic setting & Crustal deformation

- No large (M ≥ 5.5) earthquake in South Korea (1900 - early 2016)

- Unobservable crustal (fault) deformation (except for the 2011 Tohoku-Oki ep.)

(USGS) (Absolute velocities before(red) and after(blue) the 2011 Tohoku-Oki eq.: Kim et al.., 2015)

We are here

Historical & Instrumental seismicity

(KMA)

MMI > V (2-1904) 2 ≤ M ≤ 5.5 (1978-2017)

- 15 large historical earthquakes (the estimated magnitude: 6.5 < ML < 6.9)

- 10 moderate-sized (5 ≤ M ≤ 5.5) instrumental earthquakes

2017 Mw 5.42016 Mw 5.5

Active faults - Large (M ≥ 5.5) earthquakes during the Quaternary

Wangsan Fault(from Choi, W.-H.’s presentation)

YSD

YSDUC

UC

Andesite

Andesite

- Stratigraphic records data at ~ 100 sites

- No published active fault map

- Long recurrence interval of large eqs.

- We are living in long inter-seismic period

No surface rupture

ALOS-2 PALSAR images(21/07/2015 & 13/09/2016)

The 2016 MW 5.5 Gyeongju earthquake

(Elliott et al., 2016) (Kim et al., 2017)Next slide

Flow diagram of post-earthquake research No surface rupture, but aftershock sequence

(Kim et al., 2017)

Earthquake rupture on a subsidiary fault in western damage zone of the Yangsan Fault

(Central Geological Survey, Taiwan)

- Active fault map for the entire area of S. Korea

(KAFRG, 2017-2036)

- Strip map of the Central Yangsan Fault

(the epicenter area of the 2016 Gyeongju eq.)

(KIGAM, 2017-2019)

Active faults project (after the 2016 MW 5.5 Gyeongju eq.)

Development of investigation and evaluation technology for active faults in Korea

Private Advisory Board National Institute for Disaster Prevention

Main research institutePKNU

• Standardization

• Topographic analysis

• Structure analysis

• Paleoseismological

analysis

Joint research instituteKIGAM

Joint research instituteKBSI

Joint research institutePNU

Ministry of the Interior and Safety

• Topographic analysis

• Structure analysis

• Paleoseismological

analysis

• Topographic analysis

• Structure analysis

• Paleoseismological

analysis

• Development of

analysis protocol

• Dating

• Dating data verification

Committedresearch institutionChung-Ang Aero Survey

• Imaging LiDAR image

Committed research institutionSaehan Aero Survey

• Imaging LiDAR image

KAFRG (Korean Active Fault Research Group, 2017-2036)

(Haddad et al., 2012)(Howle et al., 2012)

Airborne LiDAR

Active faults project - The southern sections of the Yangsan Fault (YSF)

100 m

- Wallace Creek along the San Andreas Fault

(Sieh and Jahns, 1984; Sieh and Wallace, 1987)

Abandoned channel

Smaller horizontal displacement

along the central (?) Yangsan Fault

- Younger geomorphic marker ? - Lower slip-rate ? - Longer recurrence time ?- More distributed deformation ?

>>>

Fault Segmentation

(Wesnousky, 2006)

(Mignan et al., 2015)

- Earthquake rupture propagation is directly affected by the fault geometry and discontinuities

- Fault segmentation is an essential factor to define earthquake cycle models

Segmentation of the Yangsan Fault

Along-fault variations in geologic inheritance, geomorphic features, fault geometry, and seismic patterns

The 2017 MW 5.4 Pohang earthquake

No surface rupture, but second-order surface deformations (Choi et al., in press)

(Lee et al., 2014)(Choi et al., in press)

Surface evidence of paleo-earthquakes

Summary

- Recent two moderate-sized earthquakes occurred in the

southeastern part of the Korean Peninsula.

- There have been multiple large (M ≥ 5.5) earthquakes along

the Yangsan Fault and on its eastern block, and there are

neotectonically active crustal structures in this region.

- Geomorphic expression of the fault, which is observable in

high-resolution topographic data, plays a key role in the study

of paleo-earthquakes.

- It is needed to date more offset geomorphic markers (slip-rate)

and to excavate ‘young’ but ‘old’ stratigraphic records (temporal

history).