VOA慢速英语:加利福尼亚州开发地震预警系统

automatically –adv. done without being directly controlled by a person

on notice –adj. to be warned or told about something

detect –v. to discover or notice the presence of something

opportunity –n. an amount of time or a situation in which something can be done; a chance

seismic –adj. related to earthquakes

epicenter –n. the place on the earth that is directly above where an earthquake starts