14.3 Earth Movement and Boundaries

The January 2025 test plan lists the effect of earth movement on boundaries (earthquakes, landslide, subsidence, continental drift) as Domain IV knowledge M. Independent OpenExamPrep teaching treats that list as four physical processes that can move coordinates, move monuments, or move both, without automatically rewriting a deed. The analysis question is always: what still marks the land, and what is only a time-tagged position in a geodetic frame?

Coordinates move even when the parcel did not tear

California sits on the Pacific–North American plate boundary. Secular motion — the test plan's continental drift — changes NAD83 and CCS83 coordinates of a station from year to year even if the monument is undisturbed in the local dirt. That is why Public Resources Code 8815.1 requires that when CCS83 coordinates are shown on any map, corner record, or other document, the document shall state the datum realization tag in parentheses and the epoch date, in a decimal-year format to two decimal places, that is the basis of the values shown. The statute's own examples are forms such as CCS83 (2011) epoch 2010.00 and CCS83 (NSRS) epoch 2007.00. Mixing a 1991.35 value with a 2010.00 value and calling the residual a "bust" is not a boundary conclusion. It is an epoch mistake.

NOAA's National Geodetic Survey Horizontal Time-Dependent Positioning (HTDP) software exists to estimate those coordinate changes. Published NGS descriptions of HTDP describe a model of horizontal crustal velocities plus models of displacements from listed earthquakes, including many California events. Users can transform positional coordinates across time and between spatial reference frames, and can update certain geodetic observations from the day they were measured to another date. That is an analysis tool. HTDP does not quiet-title a lot. It does not decide which pipe is original. It does not replace a diligent monument search. Use it to bring control and GNSS vectors to a common epoch, to estimate coseismic displacement after a modeled earthquake, and to explain why this year's CCS83 value is not last decade's CCS83 value. Then go back to the monuments and the writings.

Earthquakes: block translation versus surface rupture

A felt earthquake can do two different things to a survey.

If a parcel translates as a block — the crust shifts, the lot's shape is intact, and the original monuments rode with the land — those monuments still mark that land. The coordinates of the monuments changed in the geodetic frame. The corners of the ownership did not jump to a pre-earthquake latitude and longitude. Holding a 1980s CCS83 coordinate and ignoring the pipes that moved with the hillside is how you survey the ghost of the lot instead of the lot.

If a surface rupture cuts the parcel, monuments on opposite sides of the fault have a new relative geometry. Distances and angles that once closed no longer describe the same figure. Occupation, fences, and buildings may be offset. The surveyor's job is to recover what can be recovered on each side, document the rupture, compare pre-event maps and coordinates (HTDP can help you place those older observations on a common epoch), and report the conflict. Title across a torn lot is a judicial question. Do not invent a rule that the downthrown side always keeps the house, or that the mapped fault trace is now the deed line.

Fault creep is the slow version of the same problem. The California Geological Survey describes creep on traces such as the Hayward Fault, where curbs, streets, and buildings slowly offset. Creep can bend a fence and rotate a building while the record lot lines, as writings, stay where they were. Measure the distortion. Do not silently rotate the deed to match the bent curb.

Landslides and subsidence

A landslide is local mass wasting, not plate motion. A pipe, hub, or fence post carried downhill is a displaced object. It is closer to Civil Code 1015's sudden, distinguishable movement than to Civil Code 1014's imperceptible accretion. The original corner location is a retracement problem: remaining undisturbed monuments, record geometry, and occupation that did not ride the slide. A monument found in the debris field is evidence of movement, not automatic evidence of the corner. Sudden slides also create the same occupation-versus-record pictures you analyzed in the unwritten-rights section; a garage that rode 40 feet onto the adjoiner did not complete Code of Civil Procedure 325 by moving overnight.

Subsidence is primarily vertical: groundwater withdrawal in parts of the San Joaquin Valley, oil-field compaction, peat oxidation, and similar causes. Elevations, drainage, and sometimes horizontal strain change. A vertical datum and a benchmark network can be locally deformed. Horizontal fee lines do not automatically march inland because a valley floor dropped. Report the vertical evidence, the epoch of any CCS83 values, and any measured horizontal strain. Do not treat a new orthometric height as a new sideline.

Alquist-Priolo is a planning overlay, not a boundary-move rule

The Alquist-Priolo Earthquake Fault Zoning Act is Public Resources Code 2621 and following. Public Resources Code 2621.5 states the purpose: policies and criteria to assist cities, counties, and state agencies in prohibiting the location of developments and structures for human occupancy across the trace of active faults, and to increase safety by facilitating seismic retrofitting. Public Resources Code 2622 directs the State Geologist to delineate earthquake fault zones that ordinarily are one-quarter mile or less in width around sufficiently active, well-defined traces, to issue official maps to affected cities and counties, and to revise those maps when new geologic data warrant. Sellers and agents have disclosure duties once those maps are posted.

None of that text relocates a deeded property line to the colored zone on the official map. A parcel can sit inside an earthquake fault zone and still have the same lot corners it had before the map was issued. The Act constrains where a habitable structure may be placed, not where the fee line runs. Implementing regulations used in geologic investigations presume an area near an active trace is underlain by active branches unless a geologic report shows otherwise; that is a building-setback problem for the geologist and the building official. It is not a substitute for Civil Code 830, for a senior deed, or for a recovered monument. If a client asks you to "hold the Alquist-Priolo line" as the lot line, the independent answer is no. You can show the zone on an exhibit because it affects use. You cannot use the zone as a new grant.

A Domain IV working sequence

When earth movement is in the file, work in this order:

1. Identify the process: secular drift, coseismic rupture, creep, landslide, or subsidence. They do not have the same effect on monuments.
2. Recover physical monuments and occupation. Decide which marks still sit in the land they were set to identify, and which were carried.
3. Put all geodetic values on one realization and epoch. Use HTDP (and the CCS83 tagging rule in Public Resources Code 8815.1) so you are not comparing 1993.00 with 2010.00 and calling the difference a boundary bust.
4. Overlay Alquist-Priolo and seismic-hazard maps as use and disclosure information, not as a replacement boundary.
5. Report remaining conflicts. A Record of Survey or a court exhibit can show pre-event and post-event positions. Quiet title remains a judicial act.

Exam traps. Do not treat HTDP output as a quiet-title decree. Do not treat an Alquist-Priolo zone boundary as a property line. Do not publish CCS83 values without the realization tag and two-decimal epoch. Do not hold a landslide-carried pipe as original because the brass cap still stamps the same name. Do not ignore secular motion when combining decades of GNSS control in coastal or fault-adjacent California.