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The 2015 Nepal Earthquake: Crustal deformation detected by ALOS-2 data

Crustal Deformation Observed by Synthetic Aperture Radar (SAR)

Released: Apr. 30, 2015, Last Updated: Aug. 4, 2015, Japanese version of this page

Crustal Deformation by InSAR

A Mw=7.8 (USGS) earthquake occurred in Nepal on April 25, 2015 (UTC). Applying an interferometric analysis to the data acquired by the Phased Array type L-band Synthetic Aperture Radar 2 (PALSAR-2) onboard the Advanced Land Observing Satellite 2 (ALOS-2), we have successfully detected the surface deformation associated with the earthquake.

[Features of the crustal deformation]
- Main shock on April 25 -
  • A major displacement (> 20 cm) area extends with a length of about 150 km in the east-west direction and 100 km in the north-south direction (Figs. 6 and 7).
  • Upward/downward motion is observed in the southern/northern area respectively (Fig. 6).
  • A maximum uplift about 1.4 m is observed around 20 km northeast from Kathmandu (Fig. 6).
  • There is over 1 m uplift and about 30 cm westward displacement in Kathmandu (Figs. 6 and 7). Local subsidence is also observed around the city (Fig. 5)
  • An area with large displacement caused by the main shock is consistent with an aftershock region (Figs 1, 2 and 4).
  • No clear earthquake surface fault is identified (Figs 1, 2 and 4).
- Largest aftershock on May 12 -
  • A maximum displacement (> 70 cm) moving toward the satellite is observed (Fig. 3).
  • The aftershock occurred at the area where there was no large slip for the main shock (Figs. 1-4).

[Fault model (Fig. 9)]
  • A maximum slip (> 4m) is estimated beneath the area 20-30 km northeast from Kathmandu.
  • A reverse fault motion with a slight right-lateral component is estimated on north-northeast-dipping plane, consistent with analyses by seismic waves.
  • The estimated moment magnitude is 7.9 (seismic moment 8.2×1020 Nm)
  • The largest slip is located in 80 km east-southeast of the hypocenter. The seismic rupture is thought to have propagated toward the east because there is no large slip in the western side of the hypocenter.

NOTE: The result is possibly updated with further elaborated analyses.

Interferograms

Click the images below to enlarge.

Image: Fig. 1

Fig. 1 [PNG: 2.22MB]

 

Image: Fig. 2

Fig. 2 [PNG: 1.93MB]

Image: Fig. 3

Fig. 3 [PNG: 2.70MB]

Image: Fig. 4

Fig. 4 [PNG: 2.47MB]

Image: Fig. 5

Fig. 5 [PNG: 2.04MB]

 

Fig.
#
Eq
*1
Date Time
(UTC)
Flight
Dir.
Beam
Dir.
Obs.
Mode
*2
Incidence
Angle
Bperp KMZ*3
1 M/A 2015/04/05
2015/05/17
06:13 Des. R W-W 26°-50° -95m 2.8MB
2 M 2015/04/05
2015/05/03
06:13 Des. R W-W 26°-50° +7m 2.2MB
3 A 2015/05/03
2015/05/17
06:13 Des. R W-W 26°-50° -102m 2.3MB
4 M 2014/09/20
2015/05/16
18:17 Asc. R F-W 28°-35° -397m 0.4MB
4 M 2015/02/21
2015/05/02
18:17 Asc. R F-F 33°-39° -118m 0.4MB
4 M/A 2014/11/15
2015/05/16
18:17 Asc. R F-W 38°-44° -81m 0.3MB
5 M 2014/11/07
2015/05/08
06:20 Des. R U-U 31° +301m 6.5MB

*1 Earthquakes causing the displacement. M: Main shock on April 25, A: Largest aftershock on May 12.
*2 W: ScanSAR(Normal), F: Stripmap(Fine[10m]), U: Stripmap(Ultrafine[3m]).
(cf. ALOS-2 Project / PALSAR-2 (JAXA))
*3 If the extension of the kmz file is converted from "kmz" to "zip" when you download it, please change the extension to "kmz" manually.

Analized by GSI from ALOS-2 raw data of JAXA.
These results were obtained through the activity of the SAR analysis working group of the Coordinating Committee for Earthquake Prediction.


Quasi up-down and east-west components of displacement

Click the images below to enlarge.

Image: Fig. 6

Fig. 6. Quasi up-down component [PNG: 3.01MB]

Image: Fig. 7

Fig. 7. Quasi east-west component [PNG: 3.12MB]

 

2.5-D analysis
Two or more interferograms with different observing directions can be decomposed to quasi up-down and east-west components.
Image: Geometric relation of 2.5-D analysis
Fig. 8. Geometric relation of 2.5-D analysis

Fault model

Image: Fault model
Fig. 9

Nepal Earthquake

[Main shock]
Date-Time April 25, 2015 11:56 (Local Time), April 25, 2015 06:11 (UTC)
Hypocenter Location 28.147°N, 84.708°E Depth:15.0 km (USGS, as of April 30, 2015)
Magnitude Mw=7.8 (USGS, as of April 30, 2015)
Death Toll approx. 8,900 (including by aftershocks, as of June 8, 2015)

[Largest Aftershock]
Date-Time May 12, 2015 12:50 (Local Time), May 12, 2015 07:05 (UTC)
Hypocenter Location 27.809°N, 86.066°E Depth:15.0 km (USGS, as of August 3, 2015)
Magnitude Mw=7.3 (USGS, as of May 20, 2015)

Satellite

ALOS-2 (Advanced Land Observing Satellite 2) launched by Japan Aerospace Exploration Agency on May 24, 2014

Paper, Report, Presentation

  • Kobayashi, T., Y. Morishita, and H. Yarai (2015), Detailed crustal deformation and fault rupture of the 2015 Gorkha earthquake, Nepal, revealed from ScanSAR-based interferograms of ALOS-2, Earth Planets Space, 67:201, doi:10.1186/s40623-015-0359-z. [html] [PDF: 451MB]
  • Morishita, Y., T. Kobayashi, and H. Yarai (2015), Measuring Crustal Deformation Caused by the Nepal (Gorkha) Earthquake Using ALOS-2 SAR Interferometry, S43D-2828, 2015 AGU Fall Meeting. [abstract]
  • Morishita, Y.,  T. Kobayashi and H. Yarai, Crustal deformation caused by the 2015 Nepal earthquake detected by ALOS-2 data and the fault model (Japan Geoscience Union Meeting 2015). [abstract PDF: 79KB]

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Contact

YARAI Hiroshi : Head of Division
KOBAYASHI Tomokazu : Chief Researcher
MORISHITA Yu : Researcher
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