「足元の岩の重さで重力は僅かに変わる/en」の版間の差分

2026年10月29日 (木) 13:00時点における版

#0038 Science & nature

Fact rank

A

Confirmed with primary sources (GSI, AIST, abstracts of papers in Nature and Science). Not S because the Hudson Bay share differs between studies and the size of the gravity difference was not found in a primary source

Wow rank

S

Surprising that the weight of Ice Age ice still shows up in gravity today

Usefulness

—

A fact worth knowing for its own sake

Verification: Supported by evidence

Posted by: — ・ Verified: 2026-10-29 ・ Method: AI + human ・ On Wikipedia?: Already on Wikipedia

AI verification reports the evidence it found; it does not guarantee that a claim is true.

Even at the same latitude and elevation, gravity is slightly stronger over dense rock or ore and weaker over thick sediments or cavities. Precise gravimeters can pick up the difference, so they are used in resource exploration and in surveying active faults.

Why

Gravity includes the pull of the rock beneath you, and denser rock is heavier for the same volume, so it pulls harder. Around Hudson Bay in Canada gravity is weaker than in the surrounding area, partly (roughly a quarter to a half) because crust pushed down by Ice Age ice has not yet fully rebounded.

Evidence

Primary Explanation by GSI. The size of gravity also changes with the density structure underground, and the results are used for resource exploration and estimating active faults link

Primary AIST document "Seafloor gravity exploration". The denser the ground below, the stronger the surface gravity, and the less dense, the weaker. Gravimeters can detect changes of one hundred-millionth of surface gravity and are used for resource and active-fault surveys link

Primary Abstract of Simons and Hager (1997, Nature). About half of the Hudson Bay gravity anomaly is the result of incomplete post-glacial rebound link

Primary Abstract of Tamisiea et al. (2007, Science). Models of glacial rebound that fit GRACE satellite data account for about 25 to 45% of the observed static gravity field over Hudson Bay link

Notes and limits

This is not a difference a bathroom scale can show; it takes a precise gravimeter. The rest of the Hudson Bay gravity low is thought to come mainly from mantle convection. Whether gravity is weaker over Japanese plains is not stated here because no solid source was found. The Hudson Bay gravity low is also in the Japanese Wikipedia article on Hudson Bay.

Derivations

Derived from: 重力を測ると地下の様子や火山のマグマが分かる

Derived facts: —

@@ 2行目: / 2行目: @@
 {{豆知識
 |番号=0038
-|本文=<span class="mw-translate-fuzzy">Even at the same latitude and elevation, gravity is slightly stronger over dense rock or ore and weaker over thick sediments or cavities. Precise gravimeters can pick up the difference, so they are used in resource exploration and in surveying active faults.</span>
+|本文=Even at the same latitude and elevation, gravity is slightly stronger over dense rock or ore and weaker over thick sediments or cavities. Precise gravimeters can pick up the difference, so they are used in resource exploration and in surveying active faults.
 |なぜ=Gravity includes the pull of the rock beneath you, and denser rock is heavier for the same volume, so it pulls harder. Around Hudson Bay in Canada gravity is weaker than in the surrounding area, partly (roughly a quarter to a half) because crust pushed down by Ice Age ice has not yet fully rebounded.
 |ジャンル=科学・自然