M7.1 Ridgecrest Earthquake:Line of sight displacement revealed by Sentinel-1 and ALOS-2 Interferometry


Manuscript in Review at Seismological Research Letters, September 24, 2019

Sentinel track 64 phase Sentinel track 64 phase gradient

Xiaohua Xu1, David Sandwell1, Bridget Smith-Konter2,

1Institute for Geophysics and Planetary Physics, University of California, San Diego, USA

2Department of Earth Sciences, University of Hawaii at Manoa, Honolulu, USA

IGPP SOEST

The Mw7.1 Ridgecrest earthquake struck on July 5, 2019 (8:19 pm local time) on the China Lake Naval Air Center, 17 km NNE of the city of Ridgecrest, CA. 36 hours prior, on July 4, 2019, a Mw6.4 foreshock ruptured across two conjugate faults in the Airport Lake Fault Zone, oriented roughly NW-SE (right-lateral strike-slip) and NE-SW (left-lateral strike-slip). The Mw7.1 event (right-lateral strike-slip) re-ruptured the NW-trending fault of the Mw6.4 event and also extended the rupture both to the NW and SE to at least 50 km. Field scientists report observations of 2-3 meters of right-lateral offset along the Mw7.1 rupture.

Two InSAR satellites were operational before the earthquake and continue to collect measurements of line-of-sight (LOS) deformation. The C-band Sentinel-1 satellites, operated by the European Space Agency (ESA), provide a 6-day coverage (ascending and descending tracks) of the earthquake sequence. These data are available on the Sentinel Data Hub. The L-band ALOS-2 satellite, operated by the Japanese Aerospace Exploration Agency (JAXA), collected ascending ScanSAR data for track 065 and the data can be found on the ALOS-2 User Interface Gateway.

This page is to provide near-real time line-of-sight deformation data from Sentinel-1 and ALOS-2. We will continue to provide images for each repeat pass and update the line-of-sight data once they are available. We also include KMZ files for Google Earth. The InSAR data are processed with open source software GMTSAR and mapped using Generic Mapping Tools (GMT). The InSAR phase are filtered with a 100 m Gaussian filter. The line-of-sight data are acquired by merging different swaths' phase and then unwrapped using snaphu. We also provide a higher resolution product of the immediate rupture area with range phase gradient also computed to highlight the surface fractures.

Displacement due to both the Mw6.4 (July 4, 2019) and the Mw7.1(July 5, 2019) Ridgecrest earthquakes are observed. Both wrapped interferograms and line-of-sight (LOS) displacement maps are provided below. For the Sentinel-1 interferogram maps, each fringe represents 2.8 cm of ground displacement away from the satellite. For the ALOS-2 maps, each fringe represents 12 cm of ground displacement. For ascending LOS maps, red colors (positive) indicate motion toward the satellite (up or west) and blue colors (negative) indicate motion away from the satellite (down or east). For descending LOS maps, red colors (positive) indicate motion again toward the satellite but now up or east, and blue colors (negative) indicate motion down or west.

Processed InSAR data for Modelers: (submitted to SRL data mine / Ridgecrest section. Xu and Sandwell, 2019)

data format is: #lon #lat #elevation(m) #loos_E(cosine) #look_N(cosine) #look_U(cosine) #displacement(mm) #error(-1)

- InSAR data: original LOS displacement at 500 m resolution   and downsampled detrended LOS displacement  

Fracture map: Red - right lateral; Blue - Left lateral; Black - rupture or unknown

- Surface Fracture data: KMZ file  


Fracture mapping Fracture mapping Fracture mapping Fracture mapping Fracture mapping Fracture mapping

Slip model files: (Xu et al. in prep)

- Slip model and a Matlab plotting script: Download  


Preliminary Fault Slip and Surface Deformation Models

- kmz files for Google Earth: Surface deformation models (East-West, North-South,and Vertical)  

Slip inversion uses 3 component GPS (by Peng), Sentinel-1, ALOS-2, and optical imagery fault offset (by Milliner).

Ridgecrest Slip Model
                                    Inversion Ridgecrest North-South
                                    Deformation Model Ridgecrest East-West
                                    Deformation Model Ridgecrest Vertical Deformation
                                    Model

Preliminary Coulomb Stress Change Model

- kmz-files for Google Earth: Coulomb Stress Change  

Ridgecrest Coseismic Stress
                                    Change Ridgecrest Coseismic Stress
                                    Change blank

Sentinel-1 Descending track T71: 2019/07/04 - 2019/07/16

- kmz-files for Google Earth: Phase   LOS   Phase Gradient X   Phase Gradient Y

Ridgecrest Phase Ridgecrest LOS Ridgecrest Phase Gradient Y

Sentinel-1 Ascending track T64: 2019/07/04 - 2019/07/10

- kmz-files for Google Earth: Phase   LOS   Phase Gradient X   Phase Gradient Y

Ridgecrest Phase Ridgecrest LOS Ridgecrest Phase Gradient

ALOS-2 Ascending track T66: 2017/08/12 - 2019/07/13

- kmz-files for Google Earth: Phase   LOS  Multi-Aperture Interferogram  

- note the MAI interferogram need to be corrected for ionosphere related azimuth shift before use, see Liang & Fielding (2017) for details.
Ridgecrest Phase Ridgecrest Phase Ridgecrest Multi-Aperture LOS

ALOS-2 Ascending track T65: 2016/08/08 - 2019/07/08

- kmz-files for Google Earth: Phase   LOS  Multi-Aperture Interferogram  

Ridgecrest Phase Ridgecrest Phase Ridgecrest Multi-Aperture LOS

Acknowledgements:
We thank ESA and JAXA for the rapid acquisition and distribution of their data. The development of the GMTSAR software, especially the processing chain for Sentinel-1 and ALOS-2, was supported by NASA and the National Science Foundation through the NASA Earth Surface and Interior program (NNX16AK93G and 80NSSC19K1043), the NSF Office of Advanced Cyberinfrastructure program (OAC-1834807), and the NSF EarthScope program (EAR-1147435, EAR-1424374, EAR-1614875).