Joint measurements
51,753 joint measurements from published US geologic maps, recorded as strike and dip and cited to the map each came from — 6% of the Atlas.
What it is
A joint is a brittle fracture along which the rock has parted but not slipped. No offset means no slickenlines and no sense of shear — a joint is characterised by its orientation alone, which is why it is recorded as a plane and nothing else.
Joints are rarely interesting one at a time. They form sets — populations sharing an orientation — and a rose diagram or a pole-density plot of a few hundred joints from one area resolves those sets where a map symbol cannot. Systematic sets open perpendicular to the least principal stress, so their orientation is a usable record of the stress field at the time of fracturing.
Joint measurements are unevenly distributed here. Some surveys record every set at a station; many map a joint only where it was structurally significant, so a low count for a region is often a mapping-convention fact rather than a geological one.
How the Atlas records it
Every joint row carries an azimuth and an inclination in one convention
(right-hand-rule strike and dip), a position in WGS 84 with the publisher's
own location confidence, the raw type term as the source published it, and the citation of the source map.
Selections export as CSV with a companion sources.csv of citations.
Which sources have it
| Source | Measurements | Share |
|---|---|---|
| USGS NGMDB GeMS | 11,045 | 21% |
| NPS GRI parks | 10,712 | 21% |
| USGS SIM quads (NE) | 7,639 | 15% |
| NGMDB legacy quads | 4,579 | 9% |
| South Dakota SDGS | 3,839 | 7% |
| Washington Geol. Survey | 2,165 | 4% |
| Kentucky Geol. Survey | 2,048 | 4% |
| Vermont Geol. Survey | 1,919 | 4% |
| Pennsylvania Geol. Survey | 1,377 | 3% |
| Wisconsin WGNHS | 1,377 | 3% |
| Maine Geol. Survey | 1,373 | 3% |
| Alaska DGGS | 1,296 | 3% |
| USGS data releases · MRDS | 1,174 | 2% |
| Virginia DGMR | 1,081 | 2% |
| Oregon DOGAMI (OGDC-8) | 112 | <1% |
| Idaho Geol. Survey | 13 | <1% |
| Wyoming WSGS | 4 | <1% |
Where it is
| State | Measurements | Share |
|---|---|---|
| Pennsylvania | 8,086 | 16% |
| New Hampshire | 5,459 | 11% |
| North Carolina | 4,369 | 8% |
| South Dakota | 4,333 | 8% |
| Virginia | 3,489 | 7% |
| Vermont | 2,923 | 6% |
| Maine | 2,731 | 5% |
| Arizona | 2,504 | 5% |
| Washington | 2,192 | 4% |
| Alaska | 2,187 | 4% |
| Colorado | 2,158 | 4% |
| Kentucky | 2,048 | 4% |
| Utah | 1,947 | 4% |
| New York | 1,562 | 3% |
| Wisconsin | 1,366 | 3% |
| California | 998 | 2% |
| Connecticut | 672 | 1% |
| Montana | 491 | <1% |
| New Mexico | 401 | <1% |
| New Jersey | 347 | <1% |
| Texas | 325 | <1% |
| Idaho | 289 | <1% |
| Minnesota | 209 | <1% |
| Oregon | 154 | <1% |
| West Virginia | 153 | <1% |
| Wyoming | 122 | <1% |
| Maryland | 37 | <1% |
| Kansas | 17 | <1% |
| Tennessee | 11 | <1% |
| Massachusetts | 7 | <1% |
| Illinois | 6 | <1% |
| Iowa | 5 | <1% |
| Georgia | 2 | <1% |
| Nevada | 1 | <1% |