# Aerial Mapping of Coseismic Surface Rupture of 2021 M\({}_{\rm w}\) 7.3 Maduo Earthquake, China
## 1 Introduction  
The largest Chinese earthquake, the M\({}_{\rm w}\) 7.3 Maduo earthquake, occurred in Qinghai province on 21 May 2021 since the 2008 M\({}_{\rm w}\) 7.9 Wenchuan earthquake ([[https://earthquake.usgs.gov/earthquakes/eventpage/us7000e54r/executive](https://earthquake.usgs.gov/earthquakes/eventpage/us7000e54r/executive)]([https://earthquake.usgs.gov/earthquakes/eventpage/us7000e54r/executive](https://earthquake.usgs.gov/earthquakes/eventpage/us7000e54r/executive)), accessed on 13 December 2022). Due to the high altitude and sparse population of the earthquake epicenter location, only nineteen people were injured in the earthquake ([[https://bajiiahao.baidu.com/s?id=17](https://bajiiahao.baidu.com/s?id=17)]([https://bajiiahao.baidu.com/s?id=17](https://bajiiahao.baidu.com/s?id=17)) 00968751236066246&wrf=spidere&for=pc, accessed on 13 December 2022). However, the earthquake resulted in serious damage to local buildings and infrastructure. Due to significant ground shaking, both the Yematan Bridge on the Yugong Expressway and the Changmahe Bridge on the Huaiju Expressway collapsed entirely ([[https://bajiiahao.baidu.com/s?id=1700904896415512958&wrf=spidere&for=pc](https://bajiiahao.baidu.com/s?id=1700904896415512958&wrf=spidere&for=pc)]([https://bajiiahao.baidu.com/s?id=1700904896415512958&wrf=spidere&for=pc](https://bajiiahao.baidu.com/s?id=1700904896415512958&wrf=spidere&for=pc)), accessed on 13 December 2022; Figure S1).  
Some studies have gained insight into the nature of this earthquake by performing geophysical inversions using the data recorded on seismometers and on GPS (global positioning system) instruments located near the earthquake epicenter, and satellite images collected both before and after the earthquake through differential interferometric synthetic aperture radar (D-InSAR) [1; 2; 3]. In particular, the results of D-InSAR can reflect the extension length and bifurcation of the fault on the surface, allowing for us to quickly and directly determine the impact range of the earthquake. However, due to the limited resolutions and the inconsistency between geophysical model parameters and actual geological conditions, the geophysical methods cannot completely and accurately define the distribution and offset of the coseismic surface rupture--direct observations immediately after the earthquake provide useful constraints of the rupture pattern and offset that complement the existing geophysical results.  
In the past, the field investigation of surface rupture mainly relied on the eye field of the investigator. Due to the limited height, it is difficult to grasp comprehensively therupture pattern and landform characteristics of earthquakes. With the rapid development of drone technology, it provides high-resolution and low-cost means for field observation. Through three-dimensional (3D) software, the digital elevation model (DEM), orthophoto image and 3D model of the ground surface can be obtained by processing the data collected by the drone on the site. This provides a rich database for the study of surface fracture, from which the surface fracture pattern and the displacement can be measured.  
In this study, D-InSAR was conducted to obtain the whole distribution of coseismic surface rupture. After knowing the specific location of possible rupture derived from D-InSAR, the field survey was carried out with a high-precision mapping drone, and the surface rupture data were gathered at the main rupture sites. Using the high-precision and high-resolution landform and orthophoto images obtained after data processing, the fracture combination and offset of the fault were measured. A combination of the two methods provided a scientific basis for a comprehensive understanding of the surface rupture.