2.16.3.2. pycsamt.geology.lithology#

Lithology — resistivity-to-geology classification for EM methods.

The built-in RockDatabase covers the resistivity ranges encountered in MT, AMT, CSAMT, and CSEM surveys. Its entries live in pycsamt.geology.rock_library (not in this module, so the table can grow independently of the classification logic here), drawing on:

Palacky (1988) — resistivity of geological formations
Telford, Geldart & Sheriff (1990) — Applied Geophysics
Keller & Frischknecht (1966) — Electrical Methods in Geophysical Prospecting
Slichter & Telkes (1942) — electrical properties of minerals
Updated ranges for fracture zones, aquifers, and economic targets

StratigraphicLog packages a per-station depth profile with lithology assignments and can be exported to CSV, LAS 2.0, or Oasis Montaj XYZ format via pycsamt.interp.export.

Example

>>> db = RockDatabase.default()
>>> db.classify(250.0)
RockEntry(name='Granite (weathered)', rho_min=50, rho_max=2000, ...)
>>> log = StratigraphicLog.from_column(
...     "S17", x=1050.0, z_centers=z, rho_log10=col, db=db
... )

Classes

`Layer`(top, bottom, rho_log10, lithology[, ...])	One geological unit in a pseudo-stratigraphic log.
`RockDatabase`(entries, *[, metadata])	Extensible rock physics database for EM resistivity interpretation.
`RockEntry`(name, rho_min, rho_max[, color, ...])	A single entry in the rock physics database.
`StratigraphicLog`(station_name, station_x, ...)	Per-station pseudo-stratigraphic depth profile.

class pycsamt.geology.lithology.RockEntry(name, rho_min, rho_max, color='#AAAAAA', description='', code=0, source='')[source]

Bases: PyCSAMTObject

A single entry in the rock physics database.

Parameters:

name (str) – Geological unit / lithology name.
rho_min (float) – Resistivity range in Ω·m (linear scale).
rho_max (float) – Resistivity range in Ω·m (linear scale).
color (str) – Hex colour code for plotting (e.g. '#28B463').
description (str) – Optional free-text note.
code (int) – Integer code used in LAS exports.
source (str) – Optional literature citation for this range (e.g. 'Palacky (1988)'). Empty when unspecified, as for entries loaded from a CSV without a source column.

name: str

rho_min: float

rho_max: float

color: str = '#AAAAAA'

description: str = ''

code: int = 0

source: str = ''

property rho_mid: float[source]

property log_rho_mid: float[source]

contains(rho_ohm_m)[source]

Parameters:: rho_ohm_m (float)
Return type:: bool

class pycsamt.geology.lithology.RockDatabase(entries, *, metadata=None)[source]

Bases: PyCSAMTObject, MetadataMixin

Extensible rock physics database for EM resistivity interpretation.

Parameters:

entries (list of RockEntry) – The database entries. default() returns the built-in set.
metadata (dict)

Example

>>> db = RockDatabase.default()
>>> db.classify(180.0).name
'Granite (weathered)'

metadata: dict

property entries: tuple[RockEntry, ...][source]: Read-only view of the database entries, in insertion order.

classmethod default()[source]

Return a database pre-loaded with the built-in rock entries.

Entries come from pycsamt.geology.rock_library.BUILTIN_ROCKS; see that module for the literature the ranges are drawn from.

Return type:: RockDatabase

classmethod from_csv(path)[source]

Load from a CSV file.

Required columns: name, rho_min, rho_max Optional columns: color, description, code, source

Parameters:: path (str | Path)
Return type:: RockDatabase

classmethod from_provider(provider)[source]

Build a database from any RockPropertyProvider.

This is the generic entry point behind from_url(); call it directly when provider is something other than a plain URL fetch, such as a provider pre-configured with authentication or a provider composing several sources.

Parameters:: provider (RockPropertyProvider)
Return type:: RockDatabase

classmethod from_url(url, *, cache_dir=None, ttl_seconds=86400.0, timeout=10.0, force=False, fallback=True)[source]

Fetch a database from url, with local caching and fallback.

url must serve a JSON array of objects using the same fields as RockEntry (name, rho_min, rho_max, and optionally color, description, code, source). No public rock-resistivity service is bundled or assumed by default – point this at a project- or organisation-controlled endpoint (an internal API, a shared JSON file on a file server, and so on).

Parameters:

url (str) – Location to fetch the JSON entry list from.
cache_dir (path-like, optional) – Override the local cache location. Defaults to $PYCSAMT_ROCKDB_CACHE or ~/.pycsamt/rock_db.
ttl_seconds (float) – Reuse a cached response younger than this many seconds instead of re-fetching. Default one day.
timeout (float) – Network timeout in seconds for the fetch itself.
force (bool) – Re-fetch even if a fresh cache entry exists.
fallback (bool) – If the fetch fails (network, timeout, malformed response) and no usable cache entry exists, fall back to default() instead of raising. Set to False to surface the failure instead.

Return type:

RockDatabase