## 1 Introduction  
Global navigation satellite systems (GNSS), as a primary technique of modern geodetic observation, can measure accurate crustal deformation. For a large seismic event, high-rate GNSS can provide rapid estimates of broadband displacements, including static offsets and dynamic motions of arbitrarily large magnitude [1; 2; 3; 4]. However, the errors of GNSS measurements during dynamics are systematically larger than those during static periods [5; 6; 7]. GNSS-derived dynamic motions by themselves are not accurate enough to identify millimeter-level or even smaller amplitude P-waves [8; 9].  
The strong-motion accelerometer has a superior dynamic characteristic, which is highly complementary to GNSS. Some combined processing strategies have already been presented [9; 10; 11; 12; 13; 14]. [PERSON] et al. applied a loosely coupled Kalman filter to combine high rate GNSS displacements and micro electro mechanical systems (MEMS) accelerometer data in near real time to estimate better precision in displacement. [PERSON] et al. estimated the displacement and velocity from GNSS phase observations and accelerations using a tightly coupled Kalman filter approach. These data combined strategies have no help on the accuracy improvement of GNSS carrier phase, which would deteriorate the displacement measurement precision.  
GNSS carrier phase is generated by the receiver's carrier tracking loops [15]. The tracking bandwidth and integration time play an important role on accuracy and dynamic stress tolerance [16; 17]. To reduce the noise and improve accuracy, the tracking bandwidth should be narrow and the integration time should be long. However, to be better suited for dynamic stress, wider tracking bandwidths and shorter integration times are ideal [18; 19; 20]. This causes a design contradiction of carrier tracking loops for earthquake monitoring. The majority of research on GNSS receivers for earthquake monitoring has been on the advantages of their use. There has been little research related to improving receiver measurements performance. [PERSON] et al. designed an adaptive tracking loop to overcome the design contradiction of high accuracy and dynamic stress tolerance requirements [21]. The performance of phase-locked loops (PLLs) with different integration time and bandwidth are compared under earthquake dynamics. It showed that, to obtain optimal performance, the integration time should be set as 10 ms, and the bandwidth need be changed with the dynamics. The adaptive tracking loop is capable of providing low noise before the start of an earthquake with narrow bandwidth. However, when the earthquake occurs, the tracking bandwidth would be wide enough to tolerance dynamics, which would increase the noise of carrier phase. Therefore, we focus on solving carrier phase accuracy impacted by the bandwidth.  
In navigation field, GNSS and the inertial navigation system (INS) deep couple has been studied to improve tracking loops performance under dynamic environments [22; 23]. To improve the GNSS carrier phase accuracy on earthquake monitoring, the GNSS/MEMS accelerometer deep couple must be studied. The objective of this research is to improve GNSS carrier phase accuracy using MEMS accelerometer-aided phase-locked loops (PLLs) for earthquake monitoring. The amplitude-frequency characteristics of the strong earthquake signals are studied first. Then, the measurement errors of PLLs before and after MEMS accelerometer aiding are analyzed. Furthermore, the tests based on a hardware simulator and a shake table are carried out. Results and their analysis are then presented. Finally, conclusions are shown.