Can the abyss swallow gravitational waves or why do we not observe echoes?

@article{65803,
   author = {Konoplya, Roman and Zhidenko, Alexander},
   article_number = {4},
   doi = {http://dx.doi.org/10.1209/0295-5075/ac6e00},
   keywords = {wormhole;multiple universes},
   language = {eng},
   issn = {0295-5075},
   journal = {EPL},
   title = {Can the abyss swallow gravitational waves or why do we not observe echoes?},
   url = {https://iopscience.iop.org/article/10.1209/0295-5075/ac6e00},
   volume = {138},
   year = {2022}
}

TY  - JOUR
ID  - 65803
AU  - Konoplya, Roman - Zhidenko, Alexander
PY  - 2022
TI  - Can the abyss swallow gravitational waves or why do we not observe echoes?
JF  - EPL
VL  - 138
IS  - 4
SP  - "49001-1"-"49001-5"
EP  - "49001-1"-"49001-5"
SN  - 02955075
KW  - wormhole;multiple universes
UR  - https://iopscience.iop.org/article/10.1209/0295-5075/ac6e00
N2  - Here we propose a simple explanation why echoes from wormholes mimicking black holes may be so small that they cannot be observed. The essence of the effect is in the redistribution of the initial energy of gravitational wave among multiple universes, connected by a wormhole.
ER  - 

KONOPLYA, Roman and Alexander ZHIDENKO. Can the abyss swallow gravitational waves or why do we not observe echoes? \textit{EPL}. 2022, vol.~138, No~4, p.~''49001-1''-''49001-5'', 5 pp. ISSN~0295-5075. Available from: https://dx.doi.org/10.1209/0295-5075/ac6e00.