Destroy Earthquake Epicenter X (地震源Xを倒せ Jishingen X o Taose) is the 20th episode of Ultraseven.
The Ultra Garrison have reports of earthquakes in the area, but there's something strange about them. Meanwhile, two female racers on their way to a rally find an unusual rock just as another tremor shakes the ground near Aosawa Mountains. Moroboshi and the others seek out Dr. Iwamura to help investigate the peculiar quakes in the area. They also find the two girls. The strange rock cluster they found turns out to be Ultonium -- an element found at the Earth's core. The Ultra Garrison then board the Magmalizer to burrow below the Earth's surface in the hopes of finding the answers behind the surge of earthquakes.
- Dan Moroboshi/Ultraseven (モロボシ・ダン／ウルトラセブン（声） Moroboshi Dan/Urutorasebun): Kohji Moritsugu (森次 晃嗣 Moritsugu Kōji)
- Anne Yuri (友里アンヌ Yuri Annu): Yuriko Hishimi (ひし美 ゆり子 Hishimi Yuriko)
- Shigeru Furuhashi (フルハシ・シゲル隊員 Furuhashi Shigeru): Sandayū Dokumamushi (毒蝮 三太夫 Dokumamushi Sandayū)
- Kaoru Kiriyama (キリヤマ・カオル Kiriyama Kaoru): Shoji Nakayama (中山昭二 Nakayama Shōji)
- Soga (ソガ Soga): Shinsuke Achiha (阿知波信介 Achiha Shinuske)
- Amagi (アマギ Amagi): Bin Furuya (古谷敏 Furuya Bin)
- Narrator (ナレーター Narētā): Hikaru Urano (浦野光 Urano Hikaru)
- Ultraseven (ウルトラセブン Urutorasebun): Uenishi Hirotsugu (上西弘次 Hirotsugu Uenishi)
- Ultraseven Volume 5 Features Episodes 18-21.