It appears Tilted Mills had monster attacks planned all along, and they are finally unleashing them on our city in Update #4.  In this thread of the official SimCity Societies forums, user juhhmi dug around the game’s core files and found the following in the New’s Ticker String:

Look what I found from the SCS-files (Localization, en_us, NewsTickerStrings):
“NT_MonsterSighting”>Gigantic mega monsters terrorizing nearby cities! Will ~CityName~ be next? and
“NT_MonsterSightingAftermath”>~CityName~ residents breathe a sigh of relief, ignored by rampaging monsters.

edit: More news:
“NT_Ornithosaurus”>Giant beast rampages through downtown ~CityName~. Skeptics doubtful of monster’s existence,
“NT_Ornithosaurus1”>Traffic backup caused by presence of gigantic terrifying monster in ~CItyName~. Irate commuters to arrive home late,
“NT_Burgazoid”>Robotic rampage apparently caused by baconless burger. Area bacon merchants assemble stock to appease monster and
“NT_Burgazoid1”>New and improved Burgazoid 6000 unleashed on ~CityName~, wreaks havoc. Upgrade expected shortly to remove havoc-wreaking software

edit2: More news:
“NT_OrnithosaurusAftermath”>Mysterious monster returns to nether regions of the universe — ~CityName~ prepares to rebuild, over ~cash1~ in damages sustained.,
“NT_BurgazoidAftermath”>Monster profiteers expected to do well following giant robot attack. and
“NT_BurgazoidAftermath1”>Sales of toy robots see sharp decline in wake of Burgazoid 6000’s rampage.