BEIJING — Chinese authorities in Tibet have detected problems, including cracks, at five out of 14 hydropower dams that they have inspected since a magnitude 6.8 earthquake rocked the southwest region last week, an emergency official said Thursday. Of the five affected dams, three have since been emptied, the Tibet emergency management official told a news conference. In the county of Tingri, the quake’s epicenter, the walls of one hydrodam have tilted, prompting the evacuation of about 1,500 people from six villages downstream to higher ground, he said. At another hydrodam, monitoring devices have been installed as it is being