Abstract: A release structure is disclosed for automatically closing or opening a valve on the happening of an earthquake. The release structure includes a pendulum, which is biased upwardly against stop means formed for pivotal contact with an upper end of the pendulum, the stop means and the upper end having relatively small contact area. Biasing means urges a closure member within the valve toward an open or closed position, and the closure member is releasably retained against the urging of the biasing means by latch means. A member connecting the latch means to the pendulum provides a lever which urges the pendulum upward in response to the biasing means and which releases the latch means in response to vibrationally induced swinging motion of the pendulum.