Any city office shall be declared vacant by the Council upon the occurrence of one or more or the following events before the expiration of the term or such office:
(1) For any reason specified by statute or this Charter as creating a vacancy in office;
(2) If the officer shall absent himself continuously from the City for more than sixty days without the permission of the Council;
(3) In the case of any member of the Council, if such officer shall miss four consecutive regular meetings of the Council, or twenty-five per cent of such meetings in any fiscal year of the City, unless such absences shall be excused by the Council, at the time of each absence;
(4) Assumption by the officer of any office which is incompatible with the city office held by him.