AN EMB145 FLT CREW EXPERIENCED AIRFRAME VIBRATION IN CRUISE FLT; AND PITCH TRIM WARNING LIGHTS ILLUMINATED. THEY DECLARED AN EMER AND DIVERTED TO NEAREST SUITABLE ARPT.

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DURING CRUISE FLT AT 16000 FT AND APPROX 310 KIAS; ACFT STARTED SHAKING AND FLUTTERING WITHOUT WARNING. THE AUTOPLT WAS ENGAGED AT THE TIME. A FEW SECONDS LATER THE MASTER WARNING LIGHT AND CHIME SOUNDED; WITH THE MESSAGE 'PITCH TRIM MAIN INOP' AND 'PITCH TRIM BACKUP INOP.' AT THAT TIME I DISCONNECTED THE AUTOPLT USING THE QUICK DISCONNECT BUTTON. THE ACFT WAS VERY HARD TO CTL ABOUT THE PITCH AXIS; REQUIRING EXCESSIVE FORCE INPUTS IN ORDER TO MAINTAIN CTLED AND LEVEL FLT. DECLARED EMER AND REQUESTED DIRECT ZZZ. ATC APPROVED AND GAVE A DSCNT CLRNC TO 11000 FT. AIRSPD WAS REDUCED; AND WHILE FIGHTING WITH THE VERT CTL OF THE ACFT; WE BEGAN LOSING ALT IN A SHALLOW DSCNT. VERY STRONG BACK PRESSURE HAD TO BE KEPT ON THE CTLS TO KEEP THE DSCNT SHALLOW. PITCH TRIM INDICATIONS WERE SHOWING '1' ON THE EICAS. THE FO THEN RAN THE APPROPRIATE QRH -- 'PITCH TRIM MAIN INOP.' DURING THE DSCNT TO 11000 FT; I DON'T REMEMBER THE EXACT AIRSPD; THE EICAS MESSAGES CLRED; TRIM COMMAND WAS RE-ESTABLISHED; AND PITCH CTL RETURNED TO SEEMINGLY NORMAL. WE DID NOT GO THROUGH THE CIRCUIT BREAKERS AS SUGGESTED BY THE QRH SINCE EICAS HAD CLRED. AT THIS POINT; HAVING ALREADY DECLARED THE EMER; BEGUN OUR DSCNT AND QUESTIONING OUR CONTROLLABILITY; I DETERMINED THAT LNDG AT ZZZ WOULD BE THE BEST COURSE OF ACTION. WE CONTINUED THE FLT TO ZZZ NORMALLY; WITH A NORMAL DSCNT; VISUAL APCH; AND LNDG ON RWY 35L. THE FLT ATTENDANT WAS CALLED AND TOLD OF THE DIVERSION; AND THAT WE HAD SOME EICAS MESSAGES SHOW UP; AND TO PREPARE THE CABIN FOR LNDG. THE AUTOPLT WAS NOT RE-ENGAGED DURING THE REMAINDER OF THE FLT; NOR WERE THE SPD BRAKES USED. THE EMER CREWS AT ZZZ WERE PRESENT DURING OUR LNDG AND FOLLOWED US TO OUR GATE. A MAINT WRITE-UP WAS ENTERED IN THE LOGBOOK. I SPOKE WITH DISPATCH AND MAINT CTL ONCE ON THE GND. WE WERE ASSIGNED A NEW ACFT AND CONTINUED THE FLT.SUPPLEMENTAL INFO FROM ACN 712019: WE WERE AT CRUISE FLT AT 16000 FT ABOUT 20 NM SW OF ZZZ. IT WAS A CALM AND MOSTLY CLEAR NIGHT. SUDDENLY THE AIRPLANE SHOOK VIOLENTLY; FOLLOWED BY A MASTER WARNING LIGHT AND CHIME. IMMEDIATELY AFTER THAT WE GOT TWO EICAS MESSAGES OF 'PITCH TRIM MAIN INOP' AND 'PITCH TRIM BACKUP INOP.' THE CAPT WAS THE PF AND TOOK CTL OF THE AIRPLANE BY DISCONNECTING THE AUTOPLT. AS I REACHED FOR THE QRH HE SAID THE AIRPLANE IS VERY HARD TO CONTROL AND THAT WE NEED TO GET IT ON THE GND NOW AND TO DECLARE AN EMER. I CALLED CTR AND DECLARED AN EMER. SINCE WE HAD JUST FLOWN OVER ZZZ WE DECIDED TO TURN AROUND AND LAND THERE. ATC CLRED US DIRECT TO ZZZ AND GAVE US A DSCNT CLRNC TO 11000 FT. I CONTINUED TO GO THROUGH THE QRH CHKLIST. AS I WAS GOING THROUGH THE QRH; THE 2 EICAS MESSAGES HAD CLEARED. I ASKED THE CAPT IF THE CTLS FELT ANY BETTER AND HE STATED THEY SEEMED NORMAL AGAIN. SINCE THE EICAS MESSAGES WENT AWAY; WE DID NOT ATTEMPT TO RESET THE PITCH TRIM CIRCUIT BREAKERS. HAVING ALREADY DECLARED AN EMER AND NOT FULLY SURE OF THE STATUS OF OUR FLT CTLS WE DECIDED TO CONTINUE TO ZZZ AND LAND THE AIRPLANE. I TOLD ATC THE INFO THAT THEY REQUESTED (NUMBER OF PERSONS ON BOARD AND FUEL REMAINING). WE NOTIFIED THE FLT ATTENDANT OF THE SITUATION AND TOLD HER TO PREPARE THE CABIN FOR LNDG IN ZZZ. I WENT THROUGH THE APPROPRIATE CHKLISTS (DSCNT; APCH AND LNDG). WE GOT CLRED FOR THE RWY 35L VISUAL APCH BY APCH. A NORMAL LNDG HAD BEEN ACCOMPLISHED. EMER VEHICLES MET US ON THE GND AND FOLLOWED US TO THE GATE. THE PAX WERE DEPLANED SAFELY BY JETWAY. I DID A POST FLT INSPECTION AND DID NOT NOTICE ANYTHING WRONG WITH THE AIRPLANE. ALL PITCH TRIM SYSTEMS OPERATED PROPERLY. WE NOTIFIED MAINT CTL AND DISPATCH OF THE SITUATION. LATER ON THAT EVENING WE CHANGED AIRPLANES AND CONTINUED FLT.