Count earthquakes matching filters without fetching full records. Use for statistical queries ("how many M5+ earthquakes in 2025?") or to gauge result size before calling earthquake_search. Omitting start_time counts only the last 30 days, so pass an explicit range for any period-specific question; queryEcho reports the window and filters the count actually covers. When exceeds_limit is true, the count exceeds 20,000 and a full search would be truncated — narrow filters before fetching. USGS returns the max_allowed cap (20,000); EMSC count endpoint does not return this field (max_allowed will be null). Counts can be scoped to a rectangular study area with min_latitude, max_latitude, min_longitude, and max_longitude — each independently optional. Combining the box with the lat/lon/radius circle intersects the two, counting only events inside both. Both catalogs include non-tectonic records, so a radius over a mining region counts quarry blasts alongside earthquakes — pass event_type="earthquake" on USGS to exclude them. USGS-specific filters (alert_level, event_type, min_felt, min_significance) are not sent when source=emsc — the response names them in ignoredFilters.
