# Regional Seismicity of the Northeastern Tibetan Plateau Revealed by Crustal Magnetic Anomalies
## 1 Introduction  
Earthquakes are the most dangerous of all natural disasters. Strong earthquakes can result in severe and extensive structural and non-structural damage to the built environment [1, 2]. Due to the considerable loss of life and damage caused by strong earthquakes, a variety of studies have been conducted, such as in building earthquake warning systems, as well as in the strengthening of structures and disaster management systems. With the advent of remote sensing satellites (e.g., the DEMETER, Swarm, and CSES-01 satellites), the number of statistical studies related to earthquake precursors has increased significantly. However, there have still been no reliable scientific reports on successful earthquake prediction. The northeastern Tibetan Plateau (NETP) is unique in its geographical location and tectonic activity. It is located in the northernmost part of the Tibetan Plateau at the junction of the Tibetan Plateau, Tarim Basin, Alxa-Ordos Block, and Sichuan Basin (Figure 1). The topography changes rapidly, and the crustal structure is complex due to the collision between the Indian and Eurasian plates being blocked by the Yangtze and Ordos blocks [3]. The NETP is undergoing intense northeast-directed crustal deformation, crustal shortening, and lithospheric thickening, and it is characterized by the highest level of seismicity in mainland China [4, 5]. There have been nearly 60 earthquakes of Ms \(\geq\) 6.0 in the regionin historic times [6]. As such, the NETP is an ideal region for investigating the block interactions, as well as seismotectonics. The crustal magnetic field (i.e., crustal magnetic anomalies) is generated by magnetic rocks between Earth's surface and the Curie isothermal surface (also called the Curie surface) [7]. The field is affected by factors such as geological structures, rock magnetic properties, temperature, and stress [8]. Crustal magnetic anomalies record changes in these factors [9; 10]. Crustal magnetic anomaly data have been used to estimate the Curie point depth (CPD) [11; 12; 13; 14], which is the depth at which ferromagnetic minerals are transformed into a paramagnetic state due to the increasing temperature. The interface between these phases is termed the Curie surface. Magnetite is the dominant crustal magnetic mineral as a result of its magnetic susceptibility and abundance, and it has a Curie point of 580 \({}^{\circ}\)C. Therefore, the CPD is often interpreted to be the depth of the 580 \({}^{\circ}\)C isotherm. For this reason, the CPD provides robust constraints on the thermal structure of the crust [11]. Moreover, the thermal structure may contribute to the generation and occurrence of earthquakes [14]. Information regarding crustal magnetic anomalies and the CPD obtained from crustal magnetic anomaly data can provide important insights into seismic activity and regional tectonism. Figure 1: Map of the topographic relief, major faults (black lines), GPS velocity field (blue arrows), and earthquakes (Ms \(\geq\) 5) since 1900 (red circles) in the NETP and adjacent regions. Abbreviations: F1—Altyn Tagh Fault, F2—Badain–Jaran Fault, F3—North Qilian Suture, F4—South Qilian Suture, F5—Kunlun Fault/Suture, F6—Jinsha Suture, F7—Haiyuan Fault, F8—southern margin of the Yinshan Fault, F9—Huanghe Fault, F10—western margin of the Ordos Fault, F11—northern margin of the Qinling Fault, F12—Longmengshan Fault, and F13—southern margin of the Qinling Fault. The inset at the bottom left shows the location of the study area (red box). CAOB = Central Asian Orogenic Belt; TP = Tibetan Plateau; NCC = North China Craton; YB = Yangtze Block; TB = Tarim Block; IP = Indian Plate. The purple arrow indicates direction of the IP motion. The seismic data are from the China Earthquake Networks Center, National Earthquake Data Center, and United States Geological Survey. Previous studies have used crustal magnetic anomalies to study earthquake activity. [PERSON] et al. (2012) found that magnetic anomalies in China have a close relationship with seismic structures [15]. [PERSON] et al.