This paper developed micro-electro-mechanical system (MEMS) based electrochemical seismometers featured with new structures of sensing electrodes for undersea exploration. In comparison to previously reported counterparts, the proposed sensing electrodes were featured with 1) simplification of the fabrication processes and 2) convenient control of the tiny space between anodes and cathodes by the adoption of insulating annuluses and make an increase in the sensitivities (e.g. 5200 V/(m/s) @1Hz). Based on forced-balanced feedback systems, the broadband seismometers were developed with the final bandwidth of 0.0083Hz-20Hz and achieves the sensitivity of 2000V/(m/s) with the noise level of 1.26(nm/s)/Hz^1/2@1Hz (-178dB). Under the detection of a nature earthquake, the cross-correlation coefficients between the proposed seismometers and a local seismic station reach 0.95. As a proof-of-concept demonstration, the seismometers developed in this study were tested in a sea-trial, and shown to function well on a sea bed (e.g. 1000 m in depth) with cross-correlation coefficients between two devices quantified as 0.94.