About 50 million people across Mexico felt the earthquake, which had a magnitude of 8.2, the government said. In the capital, the force of the temblor sent residents of the megacity fleeing into the streets at midnight, shaken by the alarms blaring over loudspeakers and a full minute of tremors. Windows broke, walls collapsed, and the city seemed to convulse in terrifying waves; the quake even rocked the city’s landmark Angel of Independence monument.