An echo is a reflection.  I don&#x27;t know whether gravitational waves can be reflected even in principle, but even if they can, space is so empty that in practice there&#x27;s nothing to reflect them.  So even a single massive event, like the one described in the article, will just send out a single expanding spherical wavefront; if you&#x27;re not listening at the right moment, you&#x27;ll miss it.